(* ========================================================================= *)
(* Elementary topology in Euclidean space.                                   *)
(*                                                                           *)
(*              (c) Copyright, John Harrison 1998-2008                       *)
(*              (c) Copyright, Valentina Bruno 2010                          *)
(* ========================================================================= *)

needs "Library/card.ml";;
needs "Multivariate/determinants.ml";;

(* ------------------------------------------------------------------------- *)
(* General notion of a topology.                                             *)
(* ------------------------------------------------------------------------- *)


let istopology = new_definition
 `istopology L <=>
        {} IN L /\
        (!s t. s IN L /\ t IN L ==> (s INTER t) IN L) /\
        (!k. k SUBSET L ==> (UNIONS k) IN L)`;;


let topology_tybij_th = 
prove
 (`?t:(A->bool)->bool. istopology t`,

  EXISTS_TAC `UNIV:(A->bool)->bool` THEN REWRITE_TAC[istopology; IN_UNIV]);;

let topology_tybij =
  new_type_definition "topology" ("topology","open_in") topology_tybij_th;;


let ISTOPOLOGY_OPEN_IN = 
prove
 (`istopology(open_in top)`,

  MESON_TAC[topology_tybij]);;


let TOPOLOGY_EQ = 
prove
 (`!top1 top2. top1 = top2 <=> !s. open_in top1 s <=> open_in top2 s`,

  REPEAT GEN_TAC THEN GEN_REWRITE_TAC RAND_CONV [GSYM FUN_EQ_THM] THEN
  REWRITE_TAC[ETA_AX] THEN MESON_TAC[topology_tybij]);;

(* ------------------------------------------------------------------------- *)
(* Infer the "universe" from union of all sets in the topology.              *)
(* ------------------------------------------------------------------------- *)


let topspace = new_definition
 `topspace top = UNIONS {s | open_in top s}`;;

(* ------------------------------------------------------------------------- *)
(* Main properties of open sets.                                             *)
(* ------------------------------------------------------------------------- *)


let OPEN_IN_CLAUSES = 
prove
 (`!top:(A)topology.
        open_in top {} /\
        (!s t. open_in top s /\ open_in top t ==> open_in top (s INTER t)) /\
        (!k. (!s. s IN k ==> open_in top s) ==> open_in top (UNIONS k))`,

  SIMP_TAC[IN; SUBSET; SIMP_RULE[istopology; IN; SUBSET] ISTOPOLOGY_OPEN_IN]);;


let OPEN_IN_SUBSET = 
prove
 (`!top s. open_in top s ==> s SUBSET (topspace top)`,

  REWRITE_TAC[topspace] THEN SET_TAC[]);;


let OPEN_IN_EMPTY = 
prove
 (`!top. open_in top {}`,

  REWRITE_TAC[OPEN_IN_CLAUSES]);;


let OPEN_IN_INTER = 
prove
 (`!top s t. open_in top s /\ open_in top t ==> open_in top (s INTER t)`,

  REWRITE_TAC[OPEN_IN_CLAUSES]);;


let OPEN_IN_UNIONS = 
prove
 (`!top k. (!s. s IN k ==> open_in top s) ==> open_in top (UNIONS k)`,

  REWRITE_TAC[OPEN_IN_CLAUSES]);;


let OPEN_IN_UNION = 
prove
 (`!top s t. open_in top s /\ open_in top t ==> open_in top (s UNION t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM UNIONS_2] THEN
  MATCH_MP_TAC OPEN_IN_UNIONS THEN ASM SET_TAC[]);;


let OPEN_IN_TOPSPACE = 
prove
 (`!top. open_in top (topspace top)`,

  SIMP_TAC[topspace; OPEN_IN_UNIONS; IN_ELIM_THM]);;


let OPEN_IN_INTERS = 
prove
 (`!top s:(A->bool)->bool.
        FINITE s /\ ~(s = {}) /\ (!t. t IN s ==> open_in top t)
        ==> open_in top (INTERS s)`,

  GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[INTERS_INSERT; IMP_IMP; NOT_INSERT_EMPTY; FORALL_IN_INSERT] THEN
  MAP_EVERY X_GEN_TAC [`s:A->bool`; `f:(A->bool)->bool`] THEN
  ASM_CASES_TAC `f:(A->bool)->bool = {}` THEN
  ASM_SIMP_TAC[INTERS_0; INTER_UNIV] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC OPEN_IN_INTER THEN ASM_SIMP_TAC[]);;


let OPEN_IN_SUBOPEN = 
prove
 (`!top s:A->bool.
        open_in top s <=>
        !x. x IN s ==> ?t. open_in top t /\ x IN t /\ t SUBSET s`,

  REPEAT GEN_TAC THEN EQ_TAC THENL [MESON_TAC[SUBSET_REFL]; ALL_TAC] THEN
  REWRITE_TAC[RIGHT_IMP_EXISTS_THM; SKOLEM_THM] THEN
  REWRITE_TAC[TAUT `a ==> b /\ c <=> (a ==> b) /\ (a ==> c)`] THEN
  REWRITE_TAC[FORALL_AND_THM; LEFT_IMP_EXISTS_THM] THEN
  ONCE_REWRITE_TAC[GSYM FORALL_IN_IMAGE] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP OPEN_IN_UNIONS) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Closed sets.                                                              *)
(* ------------------------------------------------------------------------- *)


let closed_in = new_definition
 `closed_in top s <=>
        s SUBSET (topspace top) /\ open_in top (topspace top DIFF s)`;;


let CLOSED_IN_SUBSET = 
prove
 (`!top s. closed_in top s ==> s SUBSET (topspace top)`,

  MESON_TAC[closed_in]);;


let CLOSED_IN_EMPTY = 
prove
 (`!top. closed_in top {}`,


let CLOSED_IN_TOPSPACE = 
prove
 (`!top. closed_in top (topspace top)`,


let CLOSED_IN_UNION = 
prove
 (`!top s t. closed_in top s /\ closed_in top t ==> closed_in top (s UNION t)`,

  SIMP_TAC[closed_in; UNION_SUBSET; OPEN_IN_INTER;
           SET_RULE `u DIFF (s UNION t) = (u DIFF s) INTER (u DIFF t)`]);;


let CLOSED_IN_INTERS = 
prove
 (`!top k:(A->bool)->bool.
        ~(k = {}) /\ (!s. s IN k ==> closed_in top s)
        ==> closed_in top (INTERS k)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[closed_in] THEN REPEAT STRIP_TAC THENL
   [ASM SET_TAC[]; ALL_TAC] THEN
  SUBGOAL_THEN `topspace top DIFF INTERS k :A->bool =
                UNIONS {topspace top DIFF s | s IN k}` SUBST1_TAC
  THENL [ALL_TAC; MATCH_MP_TAC OPEN_IN_UNIONS THEN ASM SET_TAC[]] THEN
  GEN_REWRITE_TAC I [EXTENSION] THEN ONCE_REWRITE_TAC[SIMPLE_IMAGE] THEN
  REWRITE_TAC[IN_UNIONS; IN_INTERS; IN_DIFF; EXISTS_IN_IMAGE] THEN
  MESON_TAC[]);;


let CLOSED_IN_INTER = 
prove
 (`!top s t. closed_in top s /\ closed_in top t ==> closed_in top (s INTER t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM INTERS_2] THEN
  MATCH_MP_TAC CLOSED_IN_INTERS THEN ASM SET_TAC[]);;


let OPEN_IN_CLOSED_IN_EQ = 
prove
 (`!top s. open_in top s <=>
           s SUBSET topspace top /\ closed_in top (topspace top DIFF s)`,

  REWRITE_TAC[closed_in; SET_RULE `(u DIFF s) SUBSET u`] THEN
  REWRITE_TAC[SET_RULE `u DIFF (u DIFF s) = u INTER s`] THEN
  MESON_TAC[OPEN_IN_SUBSET; SET_RULE `s SUBSET t ==> t INTER s = s`]);;


let OPEN_IN_CLOSED_IN = 
prove
 (`!s. s SUBSET topspace top
       ==> (open_in top s <=> closed_in top (topspace top DIFF s))`,

  SIMP_TAC[OPEN_IN_CLOSED_IN_EQ]);;


let OPEN_IN_DIFF = 
prove
 (`!top s t:A->bool.
      open_in top s /\ closed_in top t ==> open_in top (s DIFF t)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `s DIFF t :A->bool = s INTER (topspace top DIFF t)`
  SUBST1_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o MATCH_MP OPEN_IN_SUBSET) THEN SET_TAC[];
    MATCH_MP_TAC OPEN_IN_INTER THEN ASM_MESON_TAC[closed_in]]);;


let CLOSED_IN_DIFF = 
prove
 (`!top s t:A->bool.
        closed_in top s /\ open_in top t ==> closed_in top (s DIFF t)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `s DIFF t :A->bool = s INTER (topspace top DIFF t)`
  SUBST1_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_SUBSET) THEN SET_TAC[];
    MATCH_MP_TAC CLOSED_IN_INTER THEN ASM_MESON_TAC[OPEN_IN_CLOSED_IN_EQ]]);;


let CLOSED_IN_UNIONS = 
prove
 (`!top s. FINITE s /\ (!t. t IN s ==> closed_in top t)
           ==> closed_in top (UNIONS s)`,

  GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[UNIONS_INSERT; UNIONS_0; CLOSED_IN_EMPTY; IN_INSERT] THEN
  MESON_TAC[CLOSED_IN_UNION]);;

(* ------------------------------------------------------------------------- *)
(* Subspace topology.                                                        *)
(* ------------------------------------------------------------------------- *)


let subtopology = new_definition
 `subtopology top u = topology {s INTER u | open_in top s}`;;


let ISTOPLOGY_SUBTOPOLOGY = 
prove
 (`!top u:A->bool. istopology {s INTER u | open_in top s}`,

  REWRITE_TAC[istopology; SET_RULE
   `{s INTER u | open_in top s} =
    IMAGE (\s. s INTER u) {s | open_in top s}`] THEN
  REWRITE_TAC[IMP_CONJ; FORALL_IN_IMAGE; RIGHT_FORALL_IMP_THM] THEN
  REWRITE_TAC[SUBSET_IMAGE; IN_IMAGE; IN_ELIM_THM; SUBSET] THEN
  REPEAT GEN_TAC THEN REPEAT CONJ_TAC THENL
   [EXISTS_TAC `{}:A->bool` THEN REWRITE_TAC[OPEN_IN_EMPTY; INTER_EMPTY];
    SIMP_TAC[SET_RULE `(s INTER u) INTER t INTER u = (s INTER t) INTER u`] THEN
    ASM_MESON_TAC[OPEN_IN_INTER];
    REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`f:(A->bool)->bool`; `g:(A->bool)->bool`] THEN
    STRIP_TAC THEN EXISTS_TAC `UNIONS g :A->bool` THEN
    ASM_SIMP_TAC[OPEN_IN_UNIONS; INTER_UNIONS] THEN SET_TAC[]]);;


let OPEN_IN_SUBTOPOLOGY = 
prove
 (`!top u s. open_in (subtopology top u) s <=>
                ?t. open_in top t /\ s = t INTER u`,

  REWRITE_TAC[subtopology] THEN
  SIMP_TAC[REWRITE_RULE[CONJUNCT2 topology_tybij] ISTOPLOGY_SUBTOPOLOGY] THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM]);;


let TOPSPACE_SUBTOPOLOGY = 
prove
 (`!top u. topspace(subtopology top u) = topspace top INTER u`,

  REWRITE_TAC[topspace; OPEN_IN_SUBTOPOLOGY; INTER_UNIONS] THEN
  REPEAT STRIP_TAC THEN AP_TERM_TAC THEN
  GEN_REWRITE_TAC I [EXTENSION] THEN REWRITE_TAC[IN_ELIM_THM]);;


let CLOSED_IN_SUBTOPOLOGY = 
prove
 (`!top u s. closed_in (subtopology top u) s <=>
                ?t:A->bool. closed_in top t /\ s = t INTER u`,

  REWRITE_TAC[closed_in; TOPSPACE_SUBTOPOLOGY] THEN
  REWRITE_TAC[SUBSET_INTER; OPEN_IN_SUBTOPOLOGY; RIGHT_AND_EXISTS_THM] THEN
  REPEAT STRIP_TAC THEN EQ_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `t:A->bool` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `topspace top DIFF t :A->bool` THEN
  ASM_SIMP_TAC[CLOSED_IN_TOPSPACE; OPEN_IN_DIFF; CLOSED_IN_DIFF;
               OPEN_IN_TOPSPACE] THEN
  ASM SET_TAC[]);;


let OPEN_IN_SUBTOPOLOGY_EMPTY = 
prove
 (`!top s. open_in (subtopology top {}) s <=> s = {}`,

  REWRITE_TAC[OPEN_IN_SUBTOPOLOGY; INTER_EMPTY] THEN
  MESON_TAC[OPEN_IN_EMPTY]);;


let CLOSED_IN_SUBTOPOLOGY_EMPTY = 
prove
 (`!top s. closed_in (subtopology top {}) s <=> s = {}`,

  REWRITE_TAC[CLOSED_IN_SUBTOPOLOGY; INTER_EMPTY] THEN
  MESON_TAC[CLOSED_IN_EMPTY]);;


let OPEN_IN_SUBTOPOLOGY_REFL = 
prove
 (`!top u:A->bool. open_in (subtopology top u) u <=> u SUBSET topspace top`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_SUBTOPOLOGY] THEN EQ_TAC THENL
   [REPEAT STRIP_TAC THEN ONCE_ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC(SET_RULE `s SUBSET u ==> s INTER t SUBSET u`) THEN
    ASM_SIMP_TAC[OPEN_IN_SUBSET];
    DISCH_TAC THEN EXISTS_TAC `topspace top:A->bool` THEN
    REWRITE_TAC[OPEN_IN_TOPSPACE] THEN ASM SET_TAC[]]);;


let CLOSED_IN_SUBTOPOLOGY_REFL = 
prove
 (`!top u:A->bool. closed_in (subtopology top u) u <=> u SUBSET topspace top`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_SUBTOPOLOGY] THEN EQ_TAC THENL
   [REPEAT STRIP_TAC THEN ONCE_ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC(SET_RULE `s SUBSET u ==> s INTER t SUBSET u`) THEN
    ASM_SIMP_TAC[CLOSED_IN_SUBSET];
    DISCH_TAC THEN EXISTS_TAC `topspace top:A->bool` THEN
    REWRITE_TAC[CLOSED_IN_TOPSPACE] THEN ASM SET_TAC[]]);;


let SUBTOPOLOGY_SUPERSET = 
prove
 (`!top s:A->bool. topspace top SUBSET s ==> subtopology top s = top`,

  REPEAT GEN_TAC THEN SIMP_TAC[TOPOLOGY_EQ; OPEN_IN_SUBTOPOLOGY] THEN
  DISCH_TAC THEN X_GEN_TAC `u:A->bool` THEN EQ_TAC THENL
   [DISCH_THEN(CHOOSE_THEN(CONJUNCTS_THEN2 MP_TAC SUBST1_TAC)) THEN
    DISCH_THEN(fun th -> MP_TAC th THEN
      ASSUME_TAC(MATCH_MP OPEN_IN_SUBSET th)) THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[];
    DISCH_TAC THEN EXISTS_TAC `u:A->bool` THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP OPEN_IN_SUBSET) THEN ASM SET_TAC[]]);;


let SUBTOPOLOGY_TOPSPACE = 
prove
 (`!top. subtopology top (topspace top) = top`,


let SUBTOPOLOGY_UNIV = 
prove
 (`!top. subtopology top UNIV = top`,


let OPEN_IN_IMP_SUBSET = 
prove
 (`!top s t. open_in (subtopology top s) t ==> t SUBSET s`,

  REWRITE_TAC[OPEN_IN_SUBTOPOLOGY] THEN SET_TAC[]);;


let CLOSED_IN_IMP_SUBSET = 
prove
 (`!top s t. closed_in (subtopology top s) t ==> t SUBSET s`,

  REWRITE_TAC[closed_in; TOPSPACE_SUBTOPOLOGY] THEN SET_TAC[]);;


let OPEN_IN_SUBTOPOLOGY_UNION = 
prove
 (`!top s t u:A->bool.
        open_in (subtopology top t) s /\ open_in (subtopology top u) s
        ==> open_in (subtopology top (t UNION u)) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_SUBTOPOLOGY] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `s':A->bool` STRIP_ASSUME_TAC)
   (X_CHOOSE_THEN `t':A->bool` STRIP_ASSUME_TAC)) THEN
  EXISTS_TAC `s' INTER t':A->bool` THEN ASM_SIMP_TAC[OPEN_IN_INTER] THEN
  ASM SET_TAC[]);;


let CLOSED_IN_SUBTOPOLOGY_UNION = 
prove
 (`!top s t u:A->bool.
        closed_in (subtopology top t) s /\ closed_in (subtopology top u) s
        ==> closed_in (subtopology top (t UNION u)) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_SUBTOPOLOGY] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `s':A->bool` STRIP_ASSUME_TAC)
   (X_CHOOSE_THEN `t':A->bool` STRIP_ASSUME_TAC)) THEN
  EXISTS_TAC `s' INTER t':A->bool` THEN ASM_SIMP_TAC[CLOSED_IN_INTER] THEN
  ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* The universal Euclidean versions are what we use most of the time.        *)
(* ------------------------------------------------------------------------- *)


let open_def = new_definition
  `open s <=> !x. x IN s ==> ?e. &0 < e /\ !x'. dist(x',x) < e ==> x' IN s`;;


let closed = new_definition
  `closed(s:real^N->bool) <=> open(UNIV DIFF s)`;;


let euclidean = new_definition
 `euclidean = topology open`;;


let OPEN_EMPTY = 
prove
 (`open {}`,

  REWRITE_TAC[open_def; NOT_IN_EMPTY]);;


let OPEN_UNIV = 
prove
 (`open(:real^N)`,

  REWRITE_TAC[open_def; IN_UNIV] THEN MESON_TAC[REAL_LT_01]);;


let OPEN_INTER = 
prove
 (`!s t. open s /\ open t ==> open (s INTER t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_def; AND_FORALL_THM; IN_INTER] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_TAC `d1:real`) (X_CHOOSE_TAC `d2:real`)) THEN
  MP_TAC(SPECL [`d1:real`; `d2:real`] REAL_DOWN2) THEN
  ASM_MESON_TAC[REAL_LT_TRANS]);;


let OPEN_UNIONS = 
prove
 (`(!s. s IN f ==> open s) ==> open(UNIONS f)`,

  REWRITE_TAC[open_def; IN_UNIONS] THEN MESON_TAC[]);;


let OPEN_EXISTS_IN = 
prove
 (`!P Q:A->real^N->bool.
        (!a. P a ==> open {x | Q a x}) ==> open {x | ?a. P a /\ Q a x}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `open(UNIONS {{x | Q (a:A) (x:real^N)} | P a})` MP_TAC THENL
   [MATCH_MP_TAC OPEN_UNIONS THEN ASM_REWRITE_TAC[FORALL_IN_GSPEC];
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN REWRITE_TAC[UNIONS_GSPEC] THEN
    SET_TAC[]]);;


let OPEN_EXISTS = 
prove
 (`!Q:A->real^N->bool. (!a. open {x | Q a x}) ==> open {x | ?a. Q a x}`,

  MP_TAC(ISPEC `\x:A. T` OPEN_EXISTS_IN) THEN REWRITE_TAC[]);;


let OPEN_IN = 
prove
 (`!s:real^N->bool. open s <=> open_in euclidean s`,

  GEN_TAC THEN REWRITE_TAC[euclidean] THEN CONV_TAC SYM_CONV THEN
  AP_THM_TAC THEN REWRITE_TAC[GSYM(CONJUNCT2 topology_tybij)] THEN
  REWRITE_TAC[REWRITE_RULE[IN] istopology] THEN
  REWRITE_TAC[OPEN_EMPTY; OPEN_INTER; SUBSET] THEN
  MESON_TAC[IN; OPEN_UNIONS]);;


let TOPSPACE_EUCLIDEAN = 
prove
 (`topspace euclidean = (:real^N)`,

  REWRITE_TAC[topspace; EXTENSION; IN_UNIV; IN_UNIONS; IN_ELIM_THM] THEN
  MESON_TAC[OPEN_UNIV; IN_UNIV; OPEN_IN]);;


let TOPSPACE_EUCLIDEAN_SUBTOPOLOGY = 
prove
 (`!s. topspace (subtopology euclidean s) = s`,


let OPEN_IN_REFL = 
prove
 (`!s:real^N->bool. open_in (subtopology euclidean s) s`,


let CLOSED_IN_REFL = 
prove
 (`!s:real^N->bool. closed_in (subtopology euclidean s) s`,


let CLOSED_IN = 
prove
 (`!s:real^N->bool. closed s <=> closed_in euclidean s`,

  REWRITE_TAC[closed; closed_in; TOPSPACE_EUCLIDEAN; OPEN_IN; SUBSET_UNIV]);;


let OPEN_UNION = 
prove
 (`!s t. open s /\ open t ==> open(s UNION t)`,

  REWRITE_TAC[OPEN_IN; OPEN_IN_UNION]);;


let OPEN_SUBOPEN = 
prove
 (`!s. open s <=> !x. x IN s ==> ?t. open t /\ x IN t /\ t SUBSET s`,

  REWRITE_TAC[OPEN_IN; GSYM OPEN_IN_SUBOPEN]);;


let CLOSED_EMPTY = 
prove
 (`closed {}`,

  REWRITE_TAC[CLOSED_IN; CLOSED_IN_EMPTY]);;


let CLOSED_UNIV = 
prove
 (`closed(UNIV:real^N->bool)`,


let CLOSED_UNION = 
prove
 (`!s t. closed s /\ closed t ==> closed(s UNION t)`,

  REWRITE_TAC[CLOSED_IN; CLOSED_IN_UNION]);;


let CLOSED_INTER = 
prove
 (`!s t. closed s /\ closed t ==> closed(s INTER t)`,

  REWRITE_TAC[CLOSED_IN; CLOSED_IN_INTER]);;


let CLOSED_INTERS = 
prove
 (`!f. (!s:real^N->bool. s IN f ==> closed s) ==> closed(INTERS f)`,

  REWRITE_TAC[CLOSED_IN] THEN REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `f:(real^N->bool)->bool = {}` THEN
  ASM_SIMP_TAC[CLOSED_IN_INTERS; INTERS_0] THEN
  REWRITE_TAC[GSYM TOPSPACE_EUCLIDEAN; CLOSED_IN_TOPSPACE]);;


let CLOSED_FORALL_IN = 
prove
 (`!P Q:A->real^N->bool.
        (!a. P a ==> closed {x | Q a x}) ==> closed {x | !a. P a ==> Q a x}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `closed(INTERS {{x | Q (a:A) (x:real^N)} | P a})` MP_TAC THENL
   [MATCH_MP_TAC CLOSED_INTERS THEN ASM_REWRITE_TAC[FORALL_IN_GSPEC];
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN REWRITE_TAC[INTERS_GSPEC] THEN
    SET_TAC[]]);;


let CLOSED_FORALL = 
prove
 (`!Q:A->real^N->bool. (!a. closed {x | Q a x}) ==> closed {x | !a. Q a x}`,

  MP_TAC(ISPEC `\x:A. T` CLOSED_FORALL_IN) THEN REWRITE_TAC[]);;


let OPEN_CLOSED = 
prove
 (`!s:real^N->bool. open s <=> closed(UNIV DIFF s)`,


let OPEN_DIFF = 
prove
 (`!s t. open s /\ closed t ==> open(s DIFF t)`,

  REWRITE_TAC[OPEN_IN; CLOSED_IN; OPEN_IN_DIFF]);;


let CLOSED_DIFF = 
prove
 (`!s t. closed s /\ open t ==> closed(s DIFF t)`,

  REWRITE_TAC[OPEN_IN; CLOSED_IN; CLOSED_IN_DIFF]);;


let OPEN_INTERS = 
prove
 (`!s. FINITE s /\ (!t. t IN s ==> open t) ==> open(INTERS s)`,

  REWRITE_TAC[IMP_CONJ] THEN MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[INTERS_INSERT; INTERS_0; OPEN_UNIV; IN_INSERT] THEN
  MESON_TAC[OPEN_INTER]);;


let CLOSED_UNIONS = 
prove
 (`!s. FINITE s /\ (!t. t IN s ==> closed t) ==> closed(UNIONS s)`,

  REWRITE_TAC[IMP_CONJ] THEN MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[UNIONS_INSERT; UNIONS_0; CLOSED_EMPTY; IN_INSERT] THEN
  MESON_TAC[CLOSED_UNION]);;

(* ------------------------------------------------------------------------- *)
(* Open and closed balls and spheres.                                        *)
(* ------------------------------------------------------------------------- *)


let ball = new_definition
  `ball(x,e) = { y | dist(x,y) < e}`;;


let cball = new_definition
  `cball(x,e) = { y | dist(x,y) <= e}`;;


let sphere = new_definition
  `sphere(x,e) = { y | dist(x,y) = e}`;;


let IN_BALL = 
prove
 (`!x y e. y IN ball(x,e) <=> dist(x,y) < e`,

  REWRITE_TAC[ball; IN_ELIM_THM]);;


let IN_CBALL = 
prove
 (`!x y e. y IN cball(x,e) <=> dist(x,y) <= e`,

  REWRITE_TAC[cball; IN_ELIM_THM]);;


let IN_SPHERE = 
prove
 (`!x y e. y IN sphere(x,e) <=> dist(x,y) = e`,

  REWRITE_TAC[sphere; IN_ELIM_THM]);;


let IN_BALL_0 = 
prove
 (`!x e. x IN ball(vec 0,e) <=> norm(x) < e`,

  REWRITE_TAC[IN_BALL; dist; VECTOR_SUB_LZERO; NORM_NEG]);;


let IN_CBALL_0 = 
prove
 (`!x e. x IN cball(vec 0,e) <=> norm(x) <= e`,

  REWRITE_TAC[IN_CBALL; dist; VECTOR_SUB_LZERO; NORM_NEG]);;


let IN_SPHERE_0 = 
prove
 (`!x e. x IN sphere(vec 0,e) <=> norm(x) = e`,

  REWRITE_TAC[IN_SPHERE; dist; VECTOR_SUB_LZERO; NORM_NEG]);;


let BALL_TRIVIAL = 
prove
 (`!x. ball(x,&0) = {}`,

  REWRITE_TAC[EXTENSION; IN_BALL; IN_SING; NOT_IN_EMPTY] THEN NORM_ARITH_TAC);;


let CBALL_TRIVIAL = 
prove
 (`!x. cball(x,&0) = {x}`,

  REWRITE_TAC[EXTENSION; IN_CBALL; IN_SING; NOT_IN_EMPTY] THEN NORM_ARITH_TAC);;


let CENTRE_IN_CBALL = 
prove
 (`!x e. x IN cball(x,e) <=> &0 <= e`,

  MESON_TAC[IN_CBALL; DIST_REFL]);;


let BALL_SUBSET_CBALL = 
prove
 (`!x e. ball(x,e) SUBSET cball(x,e)`,

  REWRITE_TAC[IN_BALL; IN_CBALL; SUBSET] THEN REAL_ARITH_TAC);;


let SPHERE_SUBSET_CBALL = 
prove
 (`!x e. sphere(x,e) SUBSET cball(x,e)`,

  REWRITE_TAC[IN_SPHERE; IN_CBALL; SUBSET] THEN REAL_ARITH_TAC);;


let SUBSET_BALL = 
prove
 (`!x d e. d <= e ==> ball(x,d) SUBSET ball(x,e)`,

  REWRITE_TAC[SUBSET; IN_BALL] THEN MESON_TAC[REAL_LTE_TRANS]);;


let SUBSET_CBALL = 
prove
 (`!x d e. d <= e ==> cball(x,d) SUBSET cball(x,e)`,

  REWRITE_TAC[SUBSET; IN_CBALL] THEN MESON_TAC[REAL_LE_TRANS]);;


let BALL_MAX_UNION = 
prove
 (`!a r s. ball(a,max r s) = ball(a,r) UNION ball(a,s)`,

  REWRITE_TAC[IN_BALL; IN_UNION; EXTENSION] THEN REAL_ARITH_TAC);;


let BALL_MIN_INTER = 
prove
 (`!a r s. ball(a,min r s) = ball(a,r) INTER ball(a,s)`,

  REWRITE_TAC[IN_BALL; IN_INTER; EXTENSION] THEN REAL_ARITH_TAC);;


let CBALL_MAX_UNION = 
prove
 (`!a r s. cball(a,max r s) = cball(a,r) UNION cball(a,s)`,

  REWRITE_TAC[IN_CBALL; IN_UNION; EXTENSION] THEN REAL_ARITH_TAC);;


let CBALL_MIN_INTER = 
prove
 (`!x d e. cball(x,min d e) = cball(x,d) INTER cball(x,e)`,

  REWRITE_TAC[EXTENSION; IN_INTER; IN_CBALL] THEN REAL_ARITH_TAC);;


let BALL_TRANSLATION = 
prove
 (`!a x r. ball(a + x,r) = IMAGE (\y. a + y) (ball(x,r))`,

  REWRITE_TAC[ball] THEN GEOM_TRANSLATE_TAC[]);;


let CBALL_TRANSLATION = 
prove
 (`!a x r. cball(a + x,r) = IMAGE (\y. a + y) (cball(x,r))`,

  REWRITE_TAC[cball] THEN GEOM_TRANSLATE_TAC[]);;


let SPHERE_TRANSLATION = 
prove
 (`!a x r. sphere(a + x,r) = IMAGE (\y. a + y) (sphere(x,r))`,

  REWRITE_TAC[sphere] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants
  [BALL_TRANSLATION; CBALL_TRANSLATION; SPHERE_TRANSLATION];;


let BALL_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N x r.
        linear f /\ (!y. ?x. f x = y) /\ (!x. norm(f x) = norm x)
        ==> ball(f x,r) = IMAGE f (ball(x,r))`,

  REWRITE_TAC[ball] THEN GEOM_TRANSFORM_TAC[]);;


let CBALL_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N x r.
        linear f /\ (!y. ?x. f x = y) /\ (!x. norm(f x) = norm x)
        ==> cball(f x,r) = IMAGE f (cball(x,r))`,

  REWRITE_TAC[cball] THEN GEOM_TRANSFORM_TAC[]);;


let SPHERE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N x r.
        linear f /\ (!y. ?x. f x = y) /\ (!x. norm(f x) = norm x)
        ==> sphere(f x,r) = IMAGE f (sphere(x,r))`,

  REWRITE_TAC[sphere] THEN GEOM_TRANSFORM_TAC[]);;

add_linear_invariants
  [BALL_LINEAR_IMAGE; CBALL_LINEAR_IMAGE; SPHERE_LINEAR_IMAGE];;


let BALL_SCALING = 
prove
 (`!c. &0 < c ==> !x r. ball(c % x,c * r) = IMAGE (\x. c % x) (ball(x,r))`,

  REPEAT STRIP_TAC THEN CONV_TAC SYM_CONV THEN
  MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN REWRITE_TAC[] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[SURJECTIVE_SCALING; REAL_LT_IMP_NZ]; ALL_TAC] THEN
  REWRITE_TAC[IN_BALL; DIST_MUL] THEN
  ASM_SIMP_TAC[REAL_ARITH `&0 < c ==> abs c = c`; REAL_LT_LMUL_EQ]);;


let CBALL_SCALING = 
prove
 (`!c. &0 < c ==> !x r. cball(c % x,c * r) = IMAGE (\x. c % x) (cball(x,r))`,

  REPEAT STRIP_TAC THEN CONV_TAC SYM_CONV THEN
  MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN REWRITE_TAC[] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[SURJECTIVE_SCALING; REAL_LT_IMP_NZ]; ALL_TAC] THEN
  REWRITE_TAC[IN_CBALL; DIST_MUL] THEN
  ASM_SIMP_TAC[REAL_ARITH `&0 < c ==> abs c = c`; REAL_LE_LMUL_EQ]);;

add_scaling_theorems [BALL_SCALING; CBALL_SCALING];;


let CBALL_DIFF_BALL = 
prove
 (`!a r. cball(a,r) DIFF ball(a,r) = sphere(a,r)`,

  REWRITE_TAC[ball; cball; sphere; EXTENSION; IN_DIFF; IN_ELIM_THM] THEN
  REAL_ARITH_TAC);;


let BALL_UNION_SPHERE = 
prove
 (`!a r. ball(a,r) UNION sphere(a,r) = cball(a,r)`,

  REWRITE_TAC[ball; cball; sphere; EXTENSION; IN_UNION; IN_ELIM_THM] THEN
  REAL_ARITH_TAC);;


let SPHERE_UNION_BALL = 
prove
 (`!a r. sphere(a,r) UNION ball(a,r)  = cball(a,r)`,

  REWRITE_TAC[ball; cball; sphere; EXTENSION; IN_UNION; IN_ELIM_THM] THEN
  REAL_ARITH_TAC);;


let CBALL_DIFF_SPHERE = 
prove
 (`!a r. cball(a,r) DIFF sphere(a,r) = ball(a,r)`,

  REWRITE_TAC[EXTENSION; IN_DIFF; IN_SPHERE; IN_BALL; IN_CBALL] THEN
  REAL_ARITH_TAC);;


let OPEN_BALL = 
prove
 (`!x e. open(ball(x,e))`,

  REWRITE_TAC[open_def; ball; IN_ELIM_THM] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
  MESON_TAC[REAL_SUB_LT; REAL_LT_SUB_LADD; REAL_ADD_SYM; REAL_LET_TRANS;
            DIST_TRIANGLE_ALT]);;


let CENTRE_IN_BALL = 
prove
 (`!x e. x IN ball(x,e) <=> &0 < e`,

  MESON_TAC[IN_BALL; DIST_REFL]);;


let OPEN_CONTAINS_BALL = 
prove
 (`!s. open s <=> !x. x IN s ==> ?e. &0 < e /\ ball(x,e) SUBSET s`,

  REWRITE_TAC[open_def; SUBSET; IN_BALL] THEN REWRITE_TAC[DIST_SYM]);;


let OPEN_CONTAINS_BALL_EQ = 
prove
 (`!s. open s ==> (!x. x IN s <=> ?e. &0 < e /\ ball(x,e) SUBSET s)`,


let BALL_EQ_EMPTY = 
prove
 (`!x e. (ball(x,e) = {}) <=> e <= &0`,


let BALL_EMPTY = 
prove
 (`!x e. e <= &0 ==> ball(x,e) = {}`,

  REWRITE_TAC[BALL_EQ_EMPTY]);;


let OPEN_CONTAINS_CBALL = 
prove
 (`!s. open s <=> !x. x IN s ==> ?e. &0 < e /\ cball(x,e) SUBSET s`,

  GEN_TAC THEN REWRITE_TAC[OPEN_CONTAINS_BALL] THEN EQ_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[SUBSET_TRANS; BALL_SUBSET_CBALL]] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN
  REWRITE_TAC[SUBSET; IN_BALL; IN_CBALL] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `e / &2` THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  SUBGOAL_THEN `e / &2 < e` (fun th -> ASM_MESON_TAC[th; REAL_LET_TRANS]) THEN
  ASM_SIMP_TAC[REAL_LT_LDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
  UNDISCH_TAC `&0 < e` THEN REAL_ARITH_TAC);;


let OPEN_CONTAINS_CBALL_EQ = 
prove
 (`!s. open s ==> (!x. x IN s <=> ?e. &0 < e /\ cball(x,e) SUBSET s)`,


let SPHERE_EQ_EMPTY = 
prove
 (`!a:real^N r. sphere(a,r) = {} <=> r < &0`,

  REWRITE_TAC[sphere; EXTENSION; IN_ELIM_THM; NOT_IN_EMPTY] THEN
  REPEAT GEN_TAC THEN EQ_TAC THENL [ALL_TAC; CONV_TAC NORM_ARITH] THEN
  MESON_TAC[VECTOR_CHOOSE_DIST; REAL_NOT_LE]);;


let SPHERE_EMPTY = 
prove
 (`!a:real^N r. r < &0 ==> sphere(a,r) = {}`,

  REWRITE_TAC[SPHERE_EQ_EMPTY]);;


let NEGATIONS_BALL = 
prove
 (`!r. IMAGE (--) (ball(vec 0:real^N,r)) = ball(vec 0,r)`,

  GEN_TAC THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
  REWRITE_TAC[IN_BALL_0; NORM_NEG] THEN MESON_TAC[VECTOR_NEG_NEG]);;


let NEGATIONS_CBALL = 
prove
 (`!r. IMAGE (--) (cball(vec 0:real^N,r)) = cball(vec 0,r)`,

  GEN_TAC THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
  REWRITE_TAC[IN_CBALL_0; NORM_NEG] THEN MESON_TAC[VECTOR_NEG_NEG]);;


let NEGATIONS_SPHERE = 
prove
 (`!r. IMAGE (--) (sphere(vec 0:real^N,r)) = sphere(vec 0,r)`,

  GEN_TAC THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
  REWRITE_TAC[IN_SPHERE_0; NORM_NEG] THEN MESON_TAC[VECTOR_NEG_NEG]);;


let ORTHOGONAL_TRANSFORMATION_BALL = 
prove
 (`!f:real^N->real^N r.
    orthogonal_transformation f ==> IMAGE f (ball(vec 0,r)) = ball(vec 0,r)`,


let ORTHOGONAL_TRANSFORMATION_CBALL = 
prove
 (`!f:real^N->real^N r.
    orthogonal_transformation f ==> IMAGE f (cball(vec 0,r)) = cball(vec 0,r)`,


let ORTHOGONAL_TRANSFORMATION_SPHERE = 
prove
 (`!f:real^N->real^N r.
    orthogonal_transformation f
    ==> IMAGE f (sphere(vec 0,r)) = sphere(vec 0,r)`,

(* ------------------------------------------------------------------------- *)
(* Basic "localization" results are handy for connectedness.                 *)
(* ------------------------------------------------------------------------- *)


let OPEN_IN_OPEN = 
prove
 (`!s:real^N->bool u.
        open_in (subtopology euclidean u) s <=> ?t. open t /\ (s = u INTER t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[OPEN_IN_SUBTOPOLOGY; GSYM OPEN_IN] THEN
  REWRITE_TAC[INTER_ACI]);;


let OPEN_IN_INTER_OPEN = 
prove
 (`!s t u:real^N->bool.
        open_in (subtopology euclidean u) s /\ open t
        ==> open_in (subtopology euclidean u) (s INTER t)`,

  REWRITE_TAC[OPEN_IN_OPEN] THEN REPEAT STRIP_TAC THEN
  ASM_REWRITE_TAC[INTER_ASSOC] THEN ASM_MESON_TAC[OPEN_INTER]);;


let OPEN_IN_OPEN_INTER = 
prove
 (`!u s. open s ==> open_in (subtopology euclidean u) (u INTER s)`,

  REWRITE_TAC[OPEN_IN_OPEN] THEN MESON_TAC[]);;


let OPEN_OPEN_IN_TRANS = 
prove
 (`!s t. open s /\ open t /\ t SUBSET s
         ==> open_in (subtopology euclidean s) t`,

  MESON_TAC[OPEN_IN_OPEN_INTER; SET_RULE `t SUBSET s ==> t = s INTER t`]);;


let OPEN_SUBSET = 
prove
 (`!s t:real^N->bool.
        s SUBSET t /\ open s ==> open_in (subtopology euclidean t) s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[OPEN_IN_OPEN] THEN
  EXISTS_TAC `s:real^N->bool` THEN ASM SET_TAC[]);;


let CLOSED_IN_CLOSED = 
prove
 (`!s:real^N->bool u.
    closed_in (subtopology euclidean u) s <=> ?t. closed t /\ (s = u INTER t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CLOSED_IN_SUBTOPOLOGY; GSYM CLOSED_IN] THEN
  REWRITE_TAC[INTER_ACI]);;


let CLOSED_SUBSET_EQ = 
prove
 (`!u s:real^N->bool.
        closed s ==> (closed_in (subtopology euclidean u) s <=> s SUBSET u)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_SUBSET) THEN
    REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY];
    REWRITE_TAC[CLOSED_IN_CLOSED] THEN EXISTS_TAC `s:real^N->bool` THEN
    ASM SET_TAC[]]);;


let CLOSED_IN_INTER_CLOSED = 
prove
 (`!s t u:real^N->bool.
        closed_in (subtopology euclidean u) s /\ closed t
        ==> closed_in (subtopology euclidean u) (s INTER t)`,

  REWRITE_TAC[CLOSED_IN_CLOSED] THEN REPEAT STRIP_TAC THEN
  ASM_REWRITE_TAC[INTER_ASSOC] THEN ASM_MESON_TAC[CLOSED_INTER]);;


let CLOSED_IN_CLOSED_INTER = 
prove
 (`!u s. closed s ==> closed_in (subtopology euclidean u) (u INTER s)`,

  REWRITE_TAC[CLOSED_IN_CLOSED] THEN MESON_TAC[]);;


let CLOSED_SUBSET = 
prove
 (`!s t:real^N->bool.
        s SUBSET t /\ closed s ==> closed_in (subtopology euclidean t) s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  EXISTS_TAC `s:real^N->bool` THEN ASM SET_TAC[]);;


let OPEN_IN_SUBSET_TRANS = 
prove
 (`!s t u:real^N->bool.
        open_in (subtopology euclidean u) s /\ s SUBSET t /\ t SUBSET u
        ==> open_in (subtopology euclidean t) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_OPEN; LEFT_AND_EXISTS_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN SET_TAC[]);;


let CLOSED_IN_SUBSET_TRANS = 
prove
 (`!s t u:real^N->bool.
        closed_in (subtopology euclidean u) s /\ s SUBSET t /\ t SUBSET u
        ==> closed_in (subtopology euclidean t) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_CLOSED; LEFT_AND_EXISTS_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN SET_TAC[]);;


let open_in = 
prove
 (`!u s:real^N->bool.
        open_in (subtopology euclidean u) s <=>
          s SUBSET u /\
          !x. x IN s ==> ?e. &0 < e /\
                             !x'. x' IN u /\ dist(x',x) < e ==> x' IN s`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[OPEN_IN_SUBTOPOLOGY; GSYM OPEN_IN] THEN EQ_TAC THENL
   [REWRITE_TAC[open_def] THEN ASM SET_TAC[INTER_SUBSET; IN_INTER];
    ALL_TAC] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM] THEN DISCH_THEN(X_CHOOSE_TAC `d:real^N->real`) THEN
  EXISTS_TAC `UNIONS {b | ?x:real^N. (b = ball(x,d x)) /\ x IN s}` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC OPEN_UNIONS THEN
    ASM_SIMP_TAC[IN_ELIM_THM; LEFT_IMP_EXISTS_THM; OPEN_BALL];
    GEN_REWRITE_TAC I [EXTENSION] THEN
    REWRITE_TAC[IN_INTER; IN_UNIONS; IN_ELIM_THM] THEN
    ASM_MESON_TAC[SUBSET; DIST_REFL; DIST_SYM; IN_BALL]]);;


let OPEN_IN_CONTAINS_BALL = 
prove
 (`!s t:real^N->bool.
        open_in (subtopology euclidean t) s <=>
        s SUBSET t /\
        !x. x IN s ==> ?e. &0 < e /\ ball(x,e) INTER t SUBSET s`,

  REWRITE_TAC[open_in; INTER; SUBSET; IN_ELIM_THM; IN_BALL] THEN
  MESON_TAC[DIST_SYM]);;


let OPEN_IN_CONTAINS_CBALL = 
prove
 (`!s t:real^N->bool.
        open_in (subtopology euclidean t) s <=>
        s SUBSET t /\
        !x. x IN s ==> ?e. &0 < e /\ cball(x,e) INTER t SUBSET s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_CONTAINS_BALL] THEN
  AP_TERM_TAC THEN REWRITE_TAC[IN_BALL; IN_INTER; SUBSET; IN_CBALL] THEN
  MESON_TAC[REAL_ARITH `&0 < e ==> &0 < e / &2 /\ (x <= e / &2 ==> x < e)`;
            REAL_LT_IMP_LE]);;

(* ------------------------------------------------------------------------- *)
(* These "transitivity" results are handy too.                               *)
(* ------------------------------------------------------------------------- *)


let OPEN_IN_TRANS = 
prove
 (`!s t u. open_in (subtopology euclidean t) s /\
           open_in (subtopology euclidean u) t
           ==> open_in (subtopology euclidean u) s`,


let OPEN_IN_TRANS_EQ = 
prove
 (`!s t:real^N->bool.
        (!u. open_in (subtopology euclidean t) u
             ==> open_in (subtopology euclidean s) t)
        <=> open_in (subtopology euclidean s) t`,

  MESON_TAC[OPEN_IN_TRANS; OPEN_IN_REFL]);;


let OPEN_IN_OPEN_TRANS = 
prove
 (`!s t. open_in (subtopology euclidean t) s /\ open t ==> open s`,

  REWRITE_TAC[ONCE_REWRITE_RULE[GSYM SUBTOPOLOGY_UNIV] OPEN_IN] THEN
  REWRITE_TAC[OPEN_IN_TRANS]);;


let CLOSED_IN_TRANS = 
prove
 (`!s t u. closed_in (subtopology euclidean t) s /\
           closed_in (subtopology euclidean u) t
           ==> closed_in (subtopology euclidean u) s`,


let CLOSED_IN_TRANS_EQ = 
prove
 (`!s t:real^N->bool.
        (!u. closed_in (subtopology euclidean t) u
             ==> closed_in (subtopology euclidean s) t)
        <=> closed_in (subtopology euclidean s) t`,


let CLOSED_IN_CLOSED_TRANS = 
prove
 (`!s t. closed_in (subtopology euclidean t) s /\ closed t ==> closed s`,

  REWRITE_TAC[ONCE_REWRITE_RULE[GSYM SUBTOPOLOGY_UNIV] CLOSED_IN] THEN
  REWRITE_TAC[CLOSED_IN_TRANS]);;


let OPEN_IN_SUBTOPOLOGY_INTER_SUBSET = 
prove
 (`!s u v. open_in (subtopology euclidean u) (u INTER s) /\ v SUBSET u
           ==> open_in (subtopology euclidean v) (v INTER s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_OPEN; LEFT_AND_EXISTS_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN SET_TAC[]);;


let OPEN_IN_OPEN_EQ = 
prove
 (`!s t. open s
         ==> (open_in (subtopology euclidean s) t <=> open t /\ t SUBSET s)`,


let CLOSED_IN_CLOSED_EQ = 
prove
 (`!s t. closed s
         ==> (closed_in (subtopology euclidean s) t <=>
              closed t /\ t SUBSET s)`,

(* ------------------------------------------------------------------------- *)
(* Also some invariance theorems for relative topology.                      *)
(* ------------------------------------------------------------------------- *)


let OPEN_IN_TRANSLATION_EQ = 
prove
 (`!a s t. open_in (subtopology euclidean (IMAGE (\x. a + x) t))
                   (IMAGE (\x. a + x) s) <=>
           open_in (subtopology euclidean t) s`,

  REWRITE_TAC[open_in] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [OPEN_IN_TRANSLATION_EQ];;


let CLOSED_IN_TRANSLATION_EQ = 
prove
 (`!a s t. closed_in (subtopology euclidean (IMAGE (\x. a + x) t))
                   (IMAGE (\x. a + x) s) <=>
           closed_in (subtopology euclidean t) s`,

  REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [CLOSED_IN_TRANSLATION_EQ];;


let OPEN_IN_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s t.
          linear f /\ (!x y. f x = f y ==> x = y)
          ==> (open_in (subtopology euclidean (IMAGE f t)) (IMAGE f s) <=>
               open_in (subtopology euclidean t) s)`,

  REWRITE_TAC[open_in; FORALL_IN_IMAGE; IMP_CONJ; SUBSET] THEN
  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP (SET_RULE
   `(!x y. f x = f y ==> x = y) ==> (!x s. f x IN IMAGE f s <=> x IN s)`)) THEN
  ASM_REWRITE_TAC[] THEN
  MP_TAC(ISPEC `f:real^M->real^N` LINEAR_BOUNDED_POS) THEN
  MP_TAC(ISPEC `f:real^M->real^N` LINEAR_INJECTIVE_BOUNDED_BELOW_POS) THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `B2:real` THEN STRIP_TAC THEN
  X_GEN_TAC `B1:real` THEN STRIP_TAC THEN
  AP_TERM_TAC THEN AP_TERM_TAC THEN
  GEN_REWRITE_TAC I [FUN_EQ_THM] THEN X_GEN_TAC `x:real^M` THEN
  REWRITE_TAC[] THEN AP_TERM_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o GSYM o MATCH_MP LINEAR_SUB) THEN
  ASM_REWRITE_TAC[dist; IMP_IMP] THEN EQ_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THENL
   [EXISTS_TAC `e / B1:real`; EXISTS_TAC `e * B2:real`] THEN
  ASM_SIMP_TAC[REAL_LT_MUL; REAL_LT_DIV] THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[] THENL
   [MATCH_MP_TAC(REAL_ARITH
     `norm(f x) <= B1 * norm(x) /\ norm(x) * B1 < e ==> norm(f x) < e`) THEN
    ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ];
    MATCH_MP_TAC(REAL_ARITH
     `norm x <= norm (f x :real^N) / B2 /\ norm(f x) / B2 < e
      ==> norm x < e`) THEN
    ASM_SIMP_TAC[REAL_LE_RDIV_EQ; REAL_LT_LDIV_EQ]]);;

add_linear_invariants [OPEN_IN_INJECTIVE_LINEAR_IMAGE];;


let CLOSED_IN_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s t.
          linear f /\ (!x y. f x = f y ==> x = y)
          ==> (closed_in (subtopology euclidean (IMAGE f t)) (IMAGE f s) <=>
               closed_in (subtopology euclidean t) s)`,

  REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  GEOM_TRANSFORM_TAC[]);;

add_linear_invariants [CLOSED_IN_INJECTIVE_LINEAR_IMAGE];;

(* ------------------------------------------------------------------------- *)
(* Connectedness.                                                            *)
(* ------------------------------------------------------------------------- *)


let connected = new_definition
  `connected s <=>
      ~(?e1 e2. open e1 /\ open e2 /\ s SUBSET (e1 UNION e2) /\
                (e1 INTER e2 INTER s = {}) /\
                ~(e1 INTER s = {}) /\ ~(e2 INTER s = {}))`;;


let CONNECTED_CLOSED = 
prove
 (`!s:real^N->bool.
        connected s <=>
        ~(?e1 e2. closed e1 /\ closed e2 /\ s SUBSET (e1 UNION e2) /\
                  (e1 INTER e2 INTER s = {}) /\
                  ~(e1 INTER s = {}) /\ ~(e2 INTER s = {}))`,

  GEN_TAC THEN REWRITE_TAC[connected] THEN AP_TERM_TAC THEN
  EQ_TAC THEN REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN STRIP_TAC THEN
  MAP_EVERY EXISTS_TAC [`(:real^N) DIFF v`; `(:real^N) DIFF u`] THEN
  ASM_REWRITE_TAC[GSYM closed; GSYM OPEN_CLOSED] THEN ASM SET_TAC[]);;


let CONNECTED_OPEN_IN = 
prove
 (`!s. connected s <=>
           ~(?e1 e2.
                 open_in (subtopology euclidean s) e1 /\
                 open_in (subtopology euclidean s) e2 /\
                 s SUBSET e1 UNION e2 /\
                 e1 INTER e2 = {} /\
                 ~(e1 = {}) /\
                 ~(e2 = {}))`,

  GEN_TAC THEN REWRITE_TAC[connected; OPEN_IN_OPEN] THEN
  REWRITE_TAC[LEFT_AND_EXISTS_THM; RIGHT_AND_EXISTS_THM] THEN
  CONV_TAC(ONCE_DEPTH_CONV UNWIND_CONV) THEN
  AP_TERM_TAC THEN REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN
  SET_TAC[]);;


let CONNECTED_OPEN_IN_EQ = 
prove
 (`!s. connected s <=>
           ~(?e1 e2.
                 open_in (subtopology euclidean s) e1 /\
                 open_in (subtopology euclidean s) e2 /\
                 e1 UNION e2 = s /\ e1 INTER e2 = {} /\
                 ~(e1 = {}) /\ ~(e2 = {}))`,

  GEN_TAC THEN REWRITE_TAC[CONNECTED_OPEN_IN] THEN
  AP_TERM_TAC THEN REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN
  EQ_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[SUBSET_REFL] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[OPEN_IN_CLOSED_IN_EQ;
   TOPSPACE_EUCLIDEAN_SUBTOPOLOGY]) THEN
  ASM SET_TAC[]);;


let CONNECTED_CLOSED_IN = 
prove
 (`!s. connected s <=>
           ~(?e1 e2.
                 closed_in (subtopology euclidean s) e1 /\
                 closed_in (subtopology euclidean s) e2 /\
                 s SUBSET e1 UNION e2 /\
                 e1 INTER e2 = {} /\
                 ~(e1 = {}) /\
                 ~(e2 = {}))`,

  GEN_TAC THEN REWRITE_TAC[CONNECTED_CLOSED; CLOSED_IN_CLOSED] THEN
  REWRITE_TAC[LEFT_AND_EXISTS_THM; RIGHT_AND_EXISTS_THM] THEN
  CONV_TAC(ONCE_DEPTH_CONV UNWIND_CONV) THEN
  AP_TERM_TAC THEN REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN
  SET_TAC[]);;


let CONNECTED_CLOSED_IN_EQ = 
prove
 (`!s. connected s <=>
           ~(?e1 e2.
                 closed_in (subtopology euclidean s) e1 /\
                 closed_in (subtopology euclidean s) e2 /\

                 e1 UNION e2 = s /\ e1 INTER e2 = {} /\
                 ~(e1 = {}) /\ ~(e2 = {}))`,

  GEN_TAC THEN REWRITE_TAC[CONNECTED_CLOSED_IN] THEN
  AP_TERM_TAC THEN REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN
  EQ_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[SUBSET_REFL] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY]) THEN
  ASM SET_TAC[]);;


let CONNECTED_CLOPEN = 
prove
 (`!s. connected s <=>
        !t. open_in (subtopology euclidean s) t /\
            closed_in (subtopology euclidean s) t ==> t = {} \/ t = s`,

  GEN_TAC THEN REWRITE_TAC[connected; OPEN_IN_OPEN; CLOSED_IN_CLOSED] THEN
  GEN_REWRITE_TAC (LAND_CONV o RAND_CONV o BINDER_CONV) [GSYM EXISTS_DIFF] THEN
  ONCE_REWRITE_TAC[TAUT `(~a <=> b) <=> (a <=> ~b)`] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; GSYM CONJ_ASSOC; DE_MORGAN_THM] THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c /\ d <=> b /\ a /\ c /\ d`] THEN
  REWRITE_TAC[LEFT_AND_EXISTS_THM] THEN REWRITE_TAC[GSYM closed] THEN
  ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN AP_TERM_TAC THEN ABS_TAC THEN
  REWRITE_TAC[LEFT_AND_EXISTS_THM; RIGHT_AND_EXISTS_THM] THEN
  ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN AP_TERM_TAC THEN ABS_TAC THEN
  REWRITE_TAC[TAUT `(a /\ b) /\ (c /\ d) /\ e <=> a /\ c /\ b /\ d /\ e`] THEN
  REWRITE_TAC[RIGHT_EXISTS_AND_THM; UNWIND_THM2] THEN
  AP_TERM_TAC THEN AP_TERM_TAC THEN SET_TAC[]);;


let CONNECTED_CLOSED_SET = 
prove
 (`!s:real^N->bool.
        closed s
        ==> (connected s <=>
             ~(?e1 e2. closed e1 /\ closed e2 /\ ~(e1 = {}) /\ ~(e2 = {}) /\
                       e1 UNION e2 = s /\ e1 INTER e2 = {}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[CONNECTED_CLOSED; CONTRAPOS_THM] THEN
    REPEAT(MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC) THEN
    SIMP_TAC[] THEN SET_TAC[];
    REWRITE_TAC[CONNECTED_CLOSED_IN; CONTRAPOS_THM; LEFT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[CLOSED_IN_CLOSED; LEFT_IMP_EXISTS_THM; IMP_CONJ] THEN
    REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN REWRITE_TAC[IMP_IMP] THEN
    MAP_EVERY X_GEN_TAC
     [`e1:real^N->bool`; `e2:real^N->bool`;
      `u:real^N->bool`; `v:real^N->bool`] THEN
    STRIP_TAC THEN MAP_EVERY (C UNDISCH_THEN SUBST_ALL_TAC)
     [`e1:real^N->bool = s INTER u`;
      `e2:real^N->bool = s INTER v`] THEN
    MAP_EVERY EXISTS_TAC
     [`s INTER u:real^N->bool`; `s INTER v:real^N->bool`] THEN
    ASM_SIMP_TAC[CLOSED_INTER] THEN ASM SET_TAC[]]);;


let CONNECTED_OPEN_SET = 
prove
 (`!s:real^N->bool.
        open s
        ==> (connected s <=>
             ~(?e1 e2. open e1 /\ open e2 /\ ~(e1 = {}) /\ ~(e2 = {}) /\
                       e1 UNION e2 = s /\ e1 INTER e2 = {}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[connected; CONTRAPOS_THM] THEN
    REPEAT(MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC) THEN
    SIMP_TAC[] THEN SET_TAC[];
    REWRITE_TAC[CONNECTED_OPEN_IN; CONTRAPOS_THM; LEFT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[OPEN_IN_OPEN; LEFT_IMP_EXISTS_THM; IMP_CONJ] THEN
    REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN REWRITE_TAC[IMP_IMP] THEN
    MAP_EVERY X_GEN_TAC
     [`e1:real^N->bool`; `e2:real^N->bool`;
      `u:real^N->bool`; `v:real^N->bool`] THEN
    STRIP_TAC THEN MAP_EVERY (C UNDISCH_THEN SUBST_ALL_TAC)
     [`e1:real^N->bool = s INTER u`;
      `e2:real^N->bool = s INTER v`] THEN
    MAP_EVERY EXISTS_TAC
     [`s INTER u:real^N->bool`; `s INTER v:real^N->bool`] THEN
    ASM_SIMP_TAC[OPEN_INTER] THEN ASM SET_TAC[]]);;


let CONNECTED_EMPTY = 
prove
 (`connected {}`,

  REWRITE_TAC[connected; INTER_EMPTY]);;


let CONNECTED_SING = 
prove
 (`!a. connected{a}`,

  REWRITE_TAC[connected] THEN SET_TAC[]);;


let CONNECTED_UNIONS = 
prove
 (`!P:(real^N->bool)->bool.
        (!s. s IN P ==> connected s) /\ ~(INTERS P = {})
        ==> connected(UNIONS P)`,

  GEN_TAC THEN REWRITE_TAC[connected; NOT_EXISTS_THM] THEN STRIP_TAC THEN
  MAP_EVERY X_GEN_TAC [`e1:real^N->bool`; `e2:real^N->bool`] THEN
  STRIP_TAC THEN UNDISCH_TAC `~(INTERS P :real^N->bool = {})` THEN
  PURE_REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_INTERS] THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^N` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `(a:real^N) IN e1 \/ a IN e2` STRIP_ASSUME_TAC THENL
   [ASM SET_TAC[];
    UNDISCH_TAC `~(e2 INTER UNIONS P:real^N->bool = {})`;
    UNDISCH_TAC `~(e1 INTER UNIONS P:real^N->bool = {})`] THEN
  PURE_REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_INTER; IN_UNIONS] THEN
  DISCH_THEN(X_CHOOSE_THEN `b:real^N`
   (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  DISCH_THEN(X_CHOOSE_THEN `s:real^N->bool` STRIP_ASSUME_TAC) THEN
  UNDISCH_TAC `!t:real^N->bool. t IN P ==> a IN t` THEN
  DISCH_THEN(MP_TAC o SPEC `s:real^N->bool`) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `s:real^N->bool`) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o SPECL [`e1:real^N->bool`; `e2:real^N->bool`]) THEN
  ASM SET_TAC[]);;


let CONNECTED_UNION = 
prove
 (`!s t:real^N->bool.
        connected s /\ connected t /\ ~(s INTER t = {})
        ==> connected (s UNION t)`,

  REWRITE_TAC[GSYM UNIONS_2; GSYM INTERS_2] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_UNIONS THEN
  ASM SET_TAC[]);;


let CONNECTED_DIFF_OPEN_FROM_CLOSED = 
prove
 (`!s t u:real^N->bool.
        s SUBSET t /\ t SUBSET u /\
        open s /\ closed t /\ connected u /\ connected(t DIFF s)
        ==> connected(u DIFF s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[connected; NOT_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`v:real^N->bool`; `w:real^N->bool`] THEN STRIP_TAC THEN
  UNDISCH_TAC `connected(t DIFF s:real^N->bool)` THEN SIMP_TAC[connected] THEN
  MAP_EVERY EXISTS_TAC [`v:real^N->bool`; `w:real^N->bool`] THEN
  ASM_REWRITE_TAC[] THEN
  REPLICATE_TAC 2 (CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN
  MAP_EVERY (fun t -> SPEC_TAC(t,t)) [`v:real^N->bool`; `w:real^N->bool`] THEN
  MATCH_MP_TAC(MESON[]
   `(!v w. P v w ==> P w v) /\ (!w v. P v w /\ Q w ==> F)
    ==> !w v. P v w ==> ~(Q v) /\ ~(Q w)`) THEN
  CONJ_TAC THENL [SIMP_TAC[CONJ_ACI; INTER_ACI; UNION_ACI]; ALL_TAC] THEN
  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [connected]) THEN SIMP_TAC[] THEN
  MAP_EVERY EXISTS_TAC [`v UNION s:real^N->bool`; `w DIFF t:real^N->bool`] THEN
  ASM_SIMP_TAC[OPEN_UNION; OPEN_DIFF] THEN ASM SET_TAC[]);;


let CONNECTED_DISJOINT_UNIONS_OPEN_UNIQUE = 
prove
 (`!f:(real^N->bool)->bool f'.
         pairwise DISJOINT f /\ pairwise DISJOINT f' /\
        (!s. s IN f ==> open s /\ connected s /\ ~(s = {})) /\
        (!s. s IN f' ==> open s /\ connected s /\ ~(s = {})) /\
        UNIONS f = UNIONS f'
        ==> f = f'`,

  GEN_REWRITE_TAC (funpow 2 BINDER_CONV o RAND_CONV) [EXTENSION] THEN
  MATCH_MP_TAC(MESON[]
   `(!s t. P s t ==> P t s) /\ (!s t x. P s t /\ x IN s ==> x IN t)
    ==> (!s t. P s t ==> (!x. x IN s <=> x IN t))`) THEN
  CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
  GEN_TAC THEN GEN_TAC THEN X_GEN_TAC `s:real^N->bool` THEN STRIP_TAC THEN
  SUBGOAL_THEN
   `?t a:real^N. t IN f' /\ a IN s /\ a IN t` STRIP_ASSUME_TAC
  THENL [ASM SET_TAC[]; ALL_TAC] THEN
  SUBGOAL_THEN `s:real^N->bool = t` (fun th -> ASM_REWRITE_TAC[th]) THEN
  REWRITE_TAC[EXTENSION] THEN POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN
  MAP_EVERY (fun t -> SPEC_TAC(t,t))
   [`s:real^N->bool`; `t:real^N->bool`;
    `f:(real^N->bool)->bool`; `f':(real^N->bool)->bool`] THEN
  MATCH_MP_TAC(MESON[]
   `(!f f' s t. P f f' s t ==> P f' f t s) /\
    (!f f' s t x. P f f' s t /\ x IN s ==> x IN t)
    ==> (!f' f t s. P f f' s t ==> (!x. x IN s <=> x IN t))`) THEN
  CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
  REPLICATE_TAC 4 GEN_TAC THEN X_GEN_TAC `b:real^N` THEN STRIP_TAC THEN
  UNDISCH_TAC
   `!s:real^N->bool. s IN f ==> open s /\ connected s /\ ~(s = {})` THEN
  DISCH_THEN(MP_TAC o SPEC `s:real^N->bool`) THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN ASM_CASES_TAC `(b:real^N) IN t` THEN
  ASM_REWRITE_TAC[] THEN
  UNDISCH_TAC `connected(s:real^N->bool)` THEN
  REWRITE_TAC[connected] THEN
  MAP_EVERY EXISTS_TAC
   [`t:real^N->bool`; `UNIONS(f' DELETE (t:real^N->bool))`] THEN
  REPEAT STRIP_TAC THENL
   [ASM_SIMP_TAC[];
    MATCH_MP_TAC OPEN_UNIONS THEN ASM_SIMP_TAC[IN_DELETE];
    REWRITE_TAC[GSYM UNIONS_INSERT] THEN ASM SET_TAC[];
    MATCH_MP_TAC(SET_RULE `t INTER u = {} ==> t INTER u INTER s = {}`) THEN
    REWRITE_TAC[INTER_UNIONS; EMPTY_UNIONS; FORALL_IN_GSPEC] THEN
    REWRITE_TAC[IN_DELETE; GSYM DISJOINT] THEN ASM_MESON_TAC[pairwise];
    ASM SET_TAC[];
    ASM SET_TAC[]]);;


let CONNECTED_FROM_CLOSED_UNION_AND_INTER = 
prove
 (`!s t:real^N->bool.
        closed s /\ closed t /\ connected(s UNION t) /\ connected(s INTER t)
        ==> connected s /\ connected t`,

  MATCH_MP_TAC(MESON[]
   `(!s t. P s t ==> P t s) /\ (!s t. P s t ==> Q s)
    ==> !s t. P s t ==> Q s /\ Q t`) THEN
  CONJ_TAC THENL [SIMP_TAC[UNION_COMM; INTER_COMM]; REPEAT STRIP_TAC] THEN
  ASM_SIMP_TAC[CONNECTED_CLOSED_SET] THEN
  REWRITE_TAC[NOT_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN
  STRIP_TAC THEN ASM_CASES_TAC
   `~(s INTER t SUBSET (u:real^N->bool)) /\ ~(s INTER t SUBSET v)`
  THENL
   [UNDISCH_TAC `connected(s INTER t:real^N->bool)` THEN
    ASM_SIMP_TAC[CONNECTED_CLOSED] THEN
    MAP_EVERY EXISTS_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN
    ASM_REWRITE_TAC[] THEN ASM SET_TAC[];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [DE_MORGAN_THM]) THEN
    REWRITE_TAC[] THEN STRIP_TAC THEN
    UNDISCH_TAC `connected(s UNION t:real^N->bool)` THEN
    ASM_SIMP_TAC[CONNECTED_CLOSED] THENL
     [MAP_EVERY EXISTS_TAC [`t UNION u:real^N->bool`; `v:real^N->bool`] THEN
      ASM_SIMP_TAC[CLOSED_UNION] THEN ASM SET_TAC[];
      MAP_EVERY EXISTS_TAC [`t UNION v:real^N->bool`; `u:real^N->bool`] THEN
      ASM_SIMP_TAC[CLOSED_UNION] THEN ASM SET_TAC[]]]);;


let CONNECTED_FROM_OPEN_UNION_AND_INTER = 
prove
 (`!s t:real^N->bool.
        open s /\ open t /\ connected(s UNION t) /\ connected(s INTER t)
        ==> connected s /\ connected t`,

  MATCH_MP_TAC(MESON[]
   `(!s t. P s t ==> P t s) /\ (!s t. P s t ==> Q s)
    ==> !s t. P s t ==> Q s /\ Q t`) THEN
  CONJ_TAC THENL [SIMP_TAC[UNION_COMM; INTER_COMM]; REPEAT STRIP_TAC] THEN
  ASM_SIMP_TAC[CONNECTED_OPEN_SET] THEN
  REWRITE_TAC[NOT_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN
  STRIP_TAC THEN ASM_CASES_TAC
   `~(s INTER t SUBSET (u:real^N->bool)) /\ ~(s INTER t SUBSET v)`
  THENL
   [UNDISCH_TAC `connected(s INTER t:real^N->bool)` THEN
    ASM_SIMP_TAC[connected] THEN
    MAP_EVERY EXISTS_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN
    ASM_REWRITE_TAC[] THEN ASM SET_TAC[];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [DE_MORGAN_THM]) THEN
    REWRITE_TAC[] THEN STRIP_TAC THEN
    UNDISCH_TAC `connected(s UNION t:real^N->bool)` THEN
    ASM_SIMP_TAC[connected] THENL
     [MAP_EVERY EXISTS_TAC [`t UNION u:real^N->bool`; `v:real^N->bool`] THEN
      ASM_SIMP_TAC[OPEN_UNION] THEN ASM SET_TAC[];
      MAP_EVERY EXISTS_TAC [`t UNION v:real^N->bool`; `u:real^N->bool`] THEN
      ASM_SIMP_TAC[OPEN_UNION] THEN ASM SET_TAC[]]]);;

(* ------------------------------------------------------------------------- *)
(* Sort of induction principle for connected sets.                           *)
(* ------------------------------------------------------------------------- *)


let CONNECTED_INDUCTION = 
prove
 (`!P Q s:real^N->bool.
        connected s /\
        (!t a. open_in (subtopology euclidean s) t /\ a IN t
               ==> ?z. z IN t /\ P z) /\
        (!a. a IN s
             ==> ?t. open_in (subtopology euclidean s) t /\ a IN t /\
                     !x y. x IN t /\ y IN t /\ P x /\ P y /\ Q x ==> Q y)
        ==> !a b. a IN s /\ b IN s /\ P a /\ P b /\ Q a ==> Q b`,

  REPEAT STRIP_TAC THEN
  GEN_REWRITE_TAC I [TAUT `p <=> ~ ~p`] THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONNECTED_OPEN_IN]) THEN
  REWRITE_TAC[] THEN MAP_EVERY EXISTS_TAC
   [`{b:real^N | ?t. open_in (subtopology euclidean s) t /\ b IN t /\
                     !x. x IN t /\ P x ==> Q x}`;
    `{b:real^N | ?t. open_in (subtopology euclidean s) t /\ b IN t /\
                     !x. x IN t /\ P x ==> ~(Q x)}`] THEN
  REPEAT CONJ_TAC THENL
   [ONCE_REWRITE_TAC[OPEN_IN_SUBOPEN] THEN
    X_GEN_TAC `c:real^N` THEN REWRITE_TAC[IN_ELIM_THM] THEN
    MATCH_MP_TAC MONO_EXISTS THEN ASM SET_TAC[];
    ONCE_REWRITE_TAC[OPEN_IN_SUBOPEN] THEN
    X_GEN_TAC `c:real^N` THEN REWRITE_TAC[IN_ELIM_THM] THEN
    MATCH_MP_TAC MONO_EXISTS THEN ASM SET_TAC[];
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_UNION] THEN
    X_GEN_TAC `c:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N`) THEN ASM SET_TAC[];
    REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY; IN_ELIM_THM] THEN
    X_GEN_TAC `c:real^N` THEN DISCH_THEN(CONJUNCTS_THEN2
     (X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC)
     (X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC)) THEN
    FIRST_X_ASSUM(MP_TAC o SPECL [`t INTER u:real^N->bool`; `c:real^N`]) THEN
    ASM_SIMP_TAC[OPEN_IN_INTER] THEN ASM SET_TAC[];
    ASM SET_TAC[];
    ASM SET_TAC[]]);;


let CONNECTED_EQUIVALENCE_RELATION_GEN = 
prove
 (`!P R s:real^N->bool.
        connected s /\
        (!x y. R x y ==> R y x) /\
        (!x y z. R x y /\ R y z ==> R x z) /\
        (!t a. open_in (subtopology euclidean s) t /\ a IN t
               ==> ?z. z IN t /\ P z) /\
        (!a. a IN s
             ==> ?t. open_in (subtopology euclidean s) t /\ a IN t /\
                     !x y. x IN t /\ y IN t /\ P x /\ P y ==> R x y)
        ==> !a b. a IN s /\ b IN s /\ P a /\ P b ==> R a b`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  SUBGOAL_THEN
   `!a:real^N. a IN s /\ P a
               ==> !b c. b IN s /\ c IN s /\ P b /\ P c /\ R a b ==> R a c`
  MP_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
  GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC CONNECTED_INDUCTION THEN
  ASM_MESON_TAC[]);;


let CONNECTED_INDUCTION_SIMPLE = 
prove
 (`!P s:real^N->bool.
        connected s /\
        (!a. a IN s
             ==> ?t. open_in (subtopology euclidean s) t /\ a IN t /\
                     !x y. x IN t /\ y IN t /\ P x ==> P y)
        ==> !a b. a IN s /\ b IN s /\ P a ==> P b`,

  MP_TAC(ISPEC `\x:real^N. T` CONNECTED_INDUCTION) THEN
  REWRITE_TAC[] THEN
  REPEAT(MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN MESON_TAC[]);;


let CONNECTED_EQUIVALENCE_RELATION = 
prove
 (`!R s:real^N->bool.
        connected s /\
        (!x y. R x y ==> R y x) /\
        (!x y z. R x y /\ R y z ==> R x z) /\
        (!a. a IN s
             ==> ?t. open_in (subtopology euclidean s) t /\ a IN t /\
                     !x. x IN t ==> R a x)
        ==> !a b. a IN s /\ b IN s ==> R a b`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  SUBGOAL_THEN
   `!a:real^N. a IN s ==> !b c. b IN s /\ c IN s /\ R a b ==> R a c`
  MP_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
  GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC CONNECTED_INDUCTION_SIMPLE THEN
  ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Limit points.                                                             *)
(* ------------------------------------------------------------------------- *)

parse_as_infix ("limit_point_of",(12,"right"));;


let limit_point_of = new_definition
 `x limit_point_of s <=>
        !t. x IN t /\ open t ==> ?y. ~(y = x) /\ y IN s /\ y IN t`;;


let LIMPT_SUBSET = 
prove
 (`!x s t. x limit_point_of s /\ s SUBSET t ==> x limit_point_of t`,

  REWRITE_TAC[limit_point_of; SUBSET] THEN MESON_TAC[]);;


let LIMPT_APPROACHABLE = 
prove
 (`!x s. x limit_point_of s <=>
                !e. &0 < e ==> ?x'. x' IN s /\ ~(x' = x) /\ dist(x',x) < e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[limit_point_of] THEN
  MESON_TAC[open_def; DIST_SYM; OPEN_BALL; CENTRE_IN_BALL; IN_BALL]);;


let LIMPT_APPROACHABLE_LE = 
prove
 (`!x s. x limit_point_of s <=>
                !e. &0 < e ==> ?x'. x' IN s /\ ~(x' = x) /\ dist(x',x) <= e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE] THEN
  MATCH_MP_TAC(TAUT `(~a <=> ~b) ==> (a <=> b)`) THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM] THEN
  REWRITE_TAC[TAUT `~(a /\ b /\ c) <=> c ==> ~(a /\ b)`; APPROACHABLE_LT_LE]);;


let LIMPT_UNIV = 
prove
 (`!x:real^N. x limit_point_of UNIV`,

  GEN_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE; IN_UNIV] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  SUBGOAL_THEN `?c:real^N. norm(c) = e / &2` CHOOSE_TAC THENL
   [ASM_SIMP_TAC[VECTOR_CHOOSE_SIZE; REAL_HALF; REAL_LT_IMP_LE];
    ALL_TAC] THEN
  EXISTS_TAC `x + c:real^N` THEN
  REWRITE_TAC[dist; VECTOR_EQ_ADDR] THEN ASM_REWRITE_TAC[VECTOR_ADD_SUB] THEN
  SUBGOAL_THEN `&0 < e / &2 /\ e / &2 < e`
   (fun th -> ASM_MESON_TAC[th; NORM_0; REAL_LT_REFL]) THEN
  SIMP_TAC[REAL_LT_LDIV_EQ; REAL_LT_RDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
  UNDISCH_TAC `&0 < e` THEN REAL_ARITH_TAC);;


let CLOSED_LIMPT = 
prove
 (`!s. closed s <=> !x. x limit_point_of s ==> x IN s`,

  REWRITE_TAC[closed] THEN ONCE_REWRITE_TAC[OPEN_SUBOPEN] THEN
  REWRITE_TAC[limit_point_of; IN_DIFF; IN_UNIV; SUBSET] THEN MESON_TAC[]);;


let LIMPT_EMPTY = 
prove
 (`!x. ~(x limit_point_of {})`,

  REWRITE_TAC[LIMPT_APPROACHABLE; NOT_IN_EMPTY] THEN MESON_TAC[REAL_LT_01]);;


let NO_LIMIT_POINT_IMP_CLOSED = 
prove
 (`!s. ~(?x. x limit_point_of s) ==> closed s`,

  MESON_TAC[CLOSED_LIMPT]);;


let CLOSED_POSITIVE_ORTHANT = 
prove
 (`closed {x:real^N | !i. 1 <= i /\ i <= dimindex(:N)
                          ==> &0 <= x$i}`,

  REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE] THEN
  REWRITE_TAC[IN_ELIM_THM] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  X_GEN_TAC `i:num` THEN STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `--(x:real^N $ i)`) THEN
  ASM_REWRITE_TAC[REAL_LT_RNEG; REAL_ADD_LID; NOT_EXISTS_THM] THEN
  X_GEN_TAC `y:real^N` THEN
  MATCH_MP_TAC(TAUT `(a ==> ~c) ==> ~(a /\ b /\ c)`) THEN DISCH_TAC THEN
  MATCH_MP_TAC(REAL_ARITH `!b. abs x <= b /\ b <= a ==> ~(a + x < &0)`) THEN
  EXISTS_TAC `abs((y - x :real^N)$i)` THEN
  ASM_SIMP_TAC[dist; COMPONENT_LE_NORM] THEN
  ASM_SIMP_TAC[VECTOR_SUB_COMPONENT; REAL_ARITH
   `x < &0 /\ &0 <= y ==> abs(x) <= abs(y - x)`]);;


let FINITE_SET_AVOID = 
prove
 (`!a:real^N s. FINITE s
                ==> ?d. &0 < d /\ !x. x IN s /\ ~(x = a) ==> d <= dist(a,x)`,

  GEN_TAC THEN MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[NOT_IN_EMPTY] THEN
  CONJ_TAC THENL [MESON_TAC[REAL_LT_01]; ALL_TAC] THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `s:real^N->bool`] THEN
  DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
  FIRST_X_ASSUM(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  ASM_CASES_TAC `x:real^N = a` THEN REWRITE_TAC[IN_INSERT] THENL
   [ASM_MESON_TAC[]; ALL_TAC] THEN
  EXISTS_TAC `min d (dist(a:real^N,x))` THEN
  ASM_REWRITE_TAC[REAL_LT_MIN; GSYM DIST_NZ; REAL_MIN_LE] THEN
  ASM_MESON_TAC[REAL_LE_REFL]);;


let LIMIT_POINT_FINITE = 
prove
 (`!s a. FINITE s ==> ~(a limit_point_of s)`,

  REWRITE_TAC[LIMPT_APPROACHABLE; GSYM REAL_NOT_LE] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM; REAL_NOT_LE;
    REAL_NOT_LT; TAUT `~(a /\ b /\ c) <=> a /\ b ==> ~c`] THEN
  MESON_TAC[FINITE_SET_AVOID; DIST_SYM]);;


let LIMPT_SING = 
prove
 (`!x y:real^N. ~(x limit_point_of {y})`,


let LIMIT_POINT_UNION = 
prove
 (`!s t x:real^N. x limit_point_of (s UNION t) <=>
                  x limit_point_of s \/ x limit_point_of t`,

  REPEAT GEN_TAC THEN EQ_TAC THENL
   [ALL_TAC; MESON_TAC[LIMPT_SUBSET; SUBSET_UNION]] THEN
  REWRITE_TAC[LIMPT_APPROACHABLE; IN_UNION] THEN DISCH_TAC THEN
  MATCH_MP_TAC(TAUT `(~a ==> b) ==> a \/ b`) THEN
  REWRITE_TAC[NOT_FORALL_THM; LEFT_IMP_EXISTS_THM; NOT_IMP] THEN
  X_GEN_TAC `e:real` THEN STRIP_TAC THEN X_GEN_TAC `d:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `min d e`) THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  ASM_MESON_TAC[]);;


let LIMPT_INSERT = 
prove
 (`!s x y:real^N. x limit_point_of (y INSERT s) <=> x limit_point_of s`,

  ONCE_REWRITE_TAC[SET_RULE `y INSERT s = {y} UNION s`] THEN
  REWRITE_TAC[LIMIT_POINT_UNION] THEN
  SIMP_TAC[FINITE_SING; LIMIT_POINT_FINITE]);;


let LIMPT_OF_LIMPTS = 
prove
 (`!x:real^N s.
     x limit_point_of {y | y limit_point_of s} ==> x limit_point_of s`,

  REWRITE_TAC[LIMPT_APPROACHABLE; IN_ELIM_THM] THEN REPEAT GEN_TAC THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `dist(y:real^N,x)`) THEN
  ASM_SIMP_TAC[DIST_POS_LT] THEN MATCH_MP_TAC MONO_EXISTS THEN
  GEN_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC);;


let CLOSED_LIMPTS = 
prove
 (`!s. closed {x:real^N | x limit_point_of s}`,


let DISCRETE_IMP_CLOSED = 
prove
 (`!s:real^N->bool e.
        &0 < e /\
        (!x y. x IN s /\ y IN s /\ norm(y - x) < e ==> y = x)
        ==> closed s`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `!x:real^N. ~(x limit_point_of s)`
    (fun th -> MESON_TAC[th; CLOSED_LIMPT]) THEN
  GEN_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE] THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  REWRITE_TAC[REAL_HALF; ASSUME `&0 < e`] THEN
  DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `min (e / &2) (dist(x:real^N,y))`) THEN
  ASM_SIMP_TAC[REAL_LT_MIN; DIST_POS_LT; REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_THEN `z:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`y:real^N`; `z:real^N`]) THEN
  ASM_REWRITE_TAC[] THEN ASM_NORM_ARITH_TAC);;


let LIMPT_OF_UNIV = 
prove
 (`!x. x limit_point_of (:real^N)`,

  GEN_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE; IN_UNIV] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  MP_TAC(ISPECL [`x:real^N`; `e / &2`] VECTOR_CHOOSE_DIST) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; MATCH_MP_TAC MONO_EXISTS] THEN
  POP_ASSUM MP_TAC THEN CONV_TAC NORM_ARITH);;


let LIMPT_OF_OPEN_IN = 
prove
 (`!s t x:real^N.
        open_in (subtopology euclidean s) t /\ x limit_point_of s /\ x IN t
        ==> x limit_point_of t`,

  REWRITE_TAC[open_in; SUBSET; LIMPT_APPROACHABLE] THEN
  REPEAT GEN_TAC THEN STRIP_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `min d e / &2`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; MATCH_MP_TAC MONO_EXISTS] THEN
  GEN_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN CONJ_TAC THEN
  TRY(FIRST_X_ASSUM MATCH_MP_TAC) THEN ASM_REWRITE_TAC[] THEN
  ASM_REAL_ARITH_TAC);;


let LIMPT_OF_OPEN = 
prove
 (`!s x:real^N. open s /\ x IN s ==> x limit_point_of s`,

  REWRITE_TAC[OPEN_IN] THEN ONCE_REWRITE_TAC[GSYM SUBTOPOLOGY_UNIV] THEN
  MESON_TAC[LIMPT_OF_OPEN_IN; LIMPT_OF_UNIV]);;


let OPEN_IN_SING = 
prove
 (`!s a. open_in (subtopology euclidean s) {a} <=>
         a IN s /\ ~(a limit_point_of s)`,

  REWRITE_TAC[open_in; LIMPT_APPROACHABLE; SING_SUBSET; IN_SING] THEN
  REWRITE_TAC[FORALL_UNWIND_THM2] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Interior of a set.                                                        *)
(* ------------------------------------------------------------------------- *)


let interior = new_definition
  `interior s = {x | ?t. open t /\ x IN t /\ t SUBSET s}`;;


let INTERIOR_EQ = 
prove
 (`!s. (interior s = s) <=> open s`,

  GEN_TAC THEN REWRITE_TAC[EXTENSION; interior; IN_ELIM_THM] THEN
  GEN_REWRITE_TAC RAND_CONV [OPEN_SUBOPEN] THEN MESON_TAC[SUBSET]);;


let INTERIOR_OPEN = 
prove
 (`!s. open s ==> (interior s = s)`,

  MESON_TAC[INTERIOR_EQ]);;


let INTERIOR_EMPTY = 
prove
 (`interior {} = {}`,

  SIMP_TAC[INTERIOR_OPEN; OPEN_EMPTY]);;


let INTERIOR_UNIV = 
prove
 (`interior(:real^N) = (:real^N)`,

  SIMP_TAC[INTERIOR_OPEN; OPEN_UNIV]);;


let OPEN_INTERIOR = 
prove
 (`!s. open(interior s)`,

  GEN_TAC THEN REWRITE_TAC[interior] THEN GEN_REWRITE_TAC I [OPEN_SUBOPEN] THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN MESON_TAC[]);;


let INTERIOR_INTERIOR = 
prove
 (`!s. interior(interior s) = interior s`,

  MESON_TAC[INTERIOR_EQ; OPEN_INTERIOR]);;


let INTERIOR_SUBSET = 
prove
 (`!s. (interior s) SUBSET s`,

  REWRITE_TAC[SUBSET; interior; IN_ELIM_THM] THEN MESON_TAC[]);;


let SUBSET_INTERIOR = 
prove
 (`!s t. s SUBSET t ==> (interior s) SUBSET (interior t)`,

  REWRITE_TAC[interior; SUBSET; IN_ELIM_THM] THEN MESON_TAC[]);;


let INTERIOR_MAXIMAL = 
prove
 (`!s t. t SUBSET s /\ open t ==> t SUBSET (interior s)`,

  REWRITE_TAC[interior; SUBSET; IN_ELIM_THM] THEN MESON_TAC[]);;


let INTERIOR_MAXIMAL_EQ = 
prove
 (`!s t:real^N->bool. open s ==> (s SUBSET interior t <=> s SUBSET t)`,


let INTERIOR_UNIQUE = 
prove
 (`!s t. t SUBSET s /\ open t /\ (!t'. t' SUBSET s /\ open t' ==> t' SUBSET t)
         ==> (interior s = t)`,


let IN_INTERIOR = 
prove
 (`!x s. x IN interior s <=> ?e. &0 < e /\ ball(x,e) SUBSET s`,

  REWRITE_TAC[interior; IN_ELIM_THM] THEN
  MESON_TAC[OPEN_CONTAINS_BALL; SUBSET_TRANS; CENTRE_IN_BALL; OPEN_BALL]);;


let OPEN_SUBSET_INTERIOR = 
prove
 (`!s t. open s ==> (s SUBSET interior t <=> s SUBSET t)`,


let INTERIOR_INTER = 
prove
 (`!s t:real^N->bool. interior(s INTER t) = interior s INTER interior t`,

  REPEAT GEN_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
   [REWRITE_TAC[SUBSET_INTER] THEN CONJ_TAC THEN
    MATCH_MP_TAC SUBSET_INTERIOR THEN REWRITE_TAC[INTER_SUBSET];
    MATCH_MP_TAC INTERIOR_MAXIMAL THEN SIMP_TAC[OPEN_INTER; OPEN_INTERIOR] THEN
    MATCH_MP_TAC(SET_RULE
      `s SUBSET s' /\ t SUBSET t' ==> s INTER t SUBSET s' INTER t'`) THEN
    REWRITE_TAC[INTERIOR_SUBSET]]);;


let INTERIOR_FINITE_INTERS = 
prove
 (`!s:(real^N->bool)->bool.
        FINITE s ==> interior(INTERS s) = INTERS(IMAGE interior s)`,

  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[INTERS_0; INTERS_INSERT; INTERIOR_UNIV; IMAGE_CLAUSES] THEN
  SIMP_TAC[INTERIOR_INTER]);;


let INTERIOR_INTERS_SUBSET = 
prove
 (`!f. interior(INTERS f) SUBSET INTERS (IMAGE interior f)`,

  REWRITE_TAC[SUBSET; IN_INTERIOR; IN_INTERS; FORALL_IN_IMAGE] THEN
  MESON_TAC[]);;


let UNION_INTERIOR_SUBSET = 
prove
 (`!s t:real^N->bool.
        interior s UNION interior t SUBSET interior(s UNION t)`,

  SIMP_TAC[INTERIOR_MAXIMAL_EQ; OPEN_UNION; OPEN_INTERIOR] THEN
  REPEAT GEN_TAC THEN MATCH_MP_TAC(SET_RULE
   `s SUBSET s' /\ t SUBSET t' ==> (s UNION t) SUBSET (s' UNION t')`) THEN
  REWRITE_TAC[INTERIOR_SUBSET]);;


let INTERIOR_EQ_EMPTY = 
prove
 (`!s:real^N->bool. interior s = {} <=> !t. open t /\ t SUBSET s ==> t = {}`,


let INTERIOR_EQ_EMPTY_ALT = 
prove
 (`!s:real^N->bool.
        interior s = {} <=>
        !t. open t /\ ~(t = {}) ==> ~(t DIFF s = {})`,

  GEN_TAC THEN REWRITE_TAC[INTERIOR_EQ_EMPTY] THEN SET_TAC[]);;


let INTERIOR_LIMIT_POINT = 
prove
 (`!s x:real^N. x IN interior s ==> x limit_point_of s`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[IN_INTERIOR; IN_ELIM_THM; SUBSET; IN_BALL] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[LIMPT_APPROACHABLE] THEN X_GEN_TAC `d:real` THEN
  DISCH_TAC THEN
  MP_TAC(ISPECL [`x:real^N`; `min d e / &2`] VECTOR_CHOOSE_DIST) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  REPEAT CONJ_TAC THENL
   [FIRST_X_ASSUM MATCH_MP_TAC;
    CONV_TAC (RAND_CONV SYM_CONV) THEN REWRITE_TAC[GSYM DIST_EQ_0];
    ONCE_REWRITE_TAC[DIST_SYM]] THEN
  ASM_REAL_ARITH_TAC);;


let INTERIOR_SING = 
prove
 (`!a:real^N. interior {a} = {}`,

  REWRITE_TAC[EXTENSION; NOT_IN_EMPTY] THEN
  MESON_TAC[INTERIOR_LIMIT_POINT; LIMPT_SING]);;


let INTERIOR_CLOSED_UNION_EMPTY_INTERIOR = 
prove
 (`!s t:real^N->bool.
        closed(s) /\ interior(t) = {}
        ==> interior(s UNION t) = interior(s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  SIMP_TAC[SUBSET_INTERIOR; SUBSET_UNION] THEN
  REWRITE_TAC[SUBSET; IN_INTERIOR; IN_INTER; IN_UNION] THEN
  X_GEN_TAC `x:real^N` THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `e:real` THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  SUBGOAL_THEN `(y:real^N) limit_point_of s`
   (fun th -> ASM_MESON_TAC[CLOSED_LIMPT; th]) THEN
  REWRITE_TAC[IN_INTERIOR; NOT_IN_EMPTY; LIMPT_APPROACHABLE] THEN
  X_GEN_TAC `d:real` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `?z:real^N. ~(z IN t) /\ ~(z = y) /\ dist(z,y) < d /\ dist(x,z) < e`
   (fun th -> ASM_MESON_TAC[th; IN_BALL]) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [IN_BALL]) THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [EXTENSION]) THEN
  REWRITE_TAC[IN_INTERIOR; NOT_IN_EMPTY; NOT_EXISTS_THM] THEN
  ABBREV_TAC `k = min d (e - dist(x:real^N,y))` THEN
  SUBGOAL_THEN `&0 < k` ASSUME_TAC THENL
   [ASM_ARITH_TAC; ALL_TAC] THEN
  SUBGOAL_THEN `?w:real^N. dist(y,w) = k / &2` CHOOSE_TAC THENL
   [ASM_SIMP_TAC[VECTOR_CHOOSE_DIST; REAL_HALF; REAL_LT_IMP_LE]; ALL_TAC] THEN
  DISCH_THEN(MP_TAC o SPECL [`w:real^N`; `k / &4`]) THEN
  ASM_SIMP_TAC[SUBSET; NOT_FORALL_THM; REAL_LT_DIV; REAL_OF_NUM_LT; ARITH;
               NOT_IMP; IN_BALL] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `z:real^N` THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN ASM_REWRITE_TAC[] THEN
  ASM_NORM_ARITH_TAC);;


let INTERIOR_UNION_EQ_EMPTY = 
prove
 (`!s t:real^N->bool.
        closed s \/ closed t
        ==> (interior(s UNION t) = {} <=>
             interior s = {} /\ interior t = {})`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN EQ_TAC THENL
   [ASM_MESON_TAC[SUBSET_UNION; SUBSET_INTERIOR; SUBSET_EMPTY];
    ASM_MESON_TAC[UNION_COMM; INTERIOR_CLOSED_UNION_EMPTY_INTERIOR]]);;


let INTERIOR_UNIONS_OPEN_SUBSETS = 
prove
 (`!s:real^N->bool. UNIONS {t | open t /\ t SUBSET s} = interior s`,

  GEN_TAC THEN CONV_TAC SYM_CONV THEN MATCH_MP_TAC INTERIOR_UNIQUE THEN
  SIMP_TAC[OPEN_UNIONS; IN_ELIM_THM] THEN SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Closure of a set.                                                         *)
(* ------------------------------------------------------------------------- *)


let closure = new_definition
  `closure s = s UNION {x | x limit_point_of s}`;;


let CLOSURE_INTERIOR = 
prove
 (`!s:real^N->bool. closure s = UNIV DIFF (interior (UNIV DIFF s))`,

  REWRITE_TAC[EXTENSION; closure; IN_UNION; IN_DIFF; IN_UNIV; interior;
              IN_ELIM_THM; limit_point_of; SUBSET] THEN
  MESON_TAC[]);;


let INTERIOR_CLOSURE = 
prove
 (`!s:real^N->bool. interior s = UNIV DIFF (closure (UNIV DIFF s))`,

  
let lemma = prove(`!s t. UNIV DIFF (UNIV DIFF t) = t`,SET_TAC[]) in
  REWRITE_TAC[CLOSURE_INTERIOR; lemma]);;


let CLOSED_CLOSURE = 
prove
 (`!s. closed(closure s)`,

  
let lemma = prove(`UNIV DIFF (UNIV DIFF s) = s`,SET_TAC[]) in
  REWRITE_TAC[closed; CLOSURE_INTERIOR; lemma; OPEN_INTERIOR]);;


let CLOSURE_HULL = 
prove
 (`!s. closure s = closed hull s`,

  GEN_TAC THEN MATCH_MP_TAC(GSYM HULL_UNIQUE) THEN
  REWRITE_TAC[CLOSED_CLOSURE; SUBSET] THEN
  REWRITE_TAC[closure; IN_UNION; IN_ELIM_THM; CLOSED_LIMPT] THEN
  MESON_TAC[limit_point_of]);;


let CLOSURE_EQ = 
prove
 (`!s. (closure s = s) <=> closed s`,


let CLOSURE_CLOSED = 
prove
 (`!s. closed s ==> (closure s = s)`,

  MESON_TAC[CLOSURE_EQ]);;


let CLOSURE_CLOSURE = 
prove
 (`!s. closure(closure s) = closure s`,

  REWRITE_TAC[CLOSURE_HULL; HULL_HULL]);;


let CLOSURE_SUBSET = 
prove
 (`!s. s SUBSET (closure s)`,

  REWRITE_TAC[CLOSURE_HULL; HULL_SUBSET]);;


let SUBSET_CLOSURE = 
prove
 (`!s t. s SUBSET t ==> (closure s) SUBSET (closure t)`,

  REWRITE_TAC[CLOSURE_HULL; HULL_MONO]);;


let CLOSURE_UNION = 
prove
 (`!s t:real^N->bool. closure(s UNION t) = closure s UNION closure t`,

  REWRITE_TAC[LIMIT_POINT_UNION; closure] THEN SET_TAC[]);;


let CLOSURE_INTER_SUBSET = 
prove
 (`!s t. closure(s INTER t) SUBSET closure(s) INTER closure(t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[SUBSET_INTER] THEN
  CONJ_TAC THEN MATCH_MP_TAC SUBSET_CLOSURE THEN SET_TAC[]);;


let CLOSURE_INTERS_SUBSET = 
prove
 (`!f. closure(INTERS f) SUBSET INTERS(IMAGE closure f)`,

  REWRITE_TAC[SET_RULE `s SUBSET INTERS f <=> !t. t IN f ==> s SUBSET t`] THEN
  REWRITE_TAC[FORALL_IN_IMAGE] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SUBSET_CLOSURE THEN ASM SET_TAC[]);;


let CLOSURE_MINIMAL = 
prove
 (`!s t. s SUBSET t /\ closed t ==> (closure s) SUBSET t`,

  REWRITE_TAC[HULL_MINIMAL; CLOSURE_HULL]);;


let CLOSURE_MINIMAL_EQ = 
prove
 (`!s t:real^N->bool. closed t ==> (closure s SUBSET t <=> s SUBSET t)`,


let CLOSURE_UNIQUE = 
prove
 (`!s t. s SUBSET t /\ closed t /\
         (!t'. s SUBSET t' /\ closed t' ==> t SUBSET t')
         ==> (closure s = t)`,

  REWRITE_TAC[CLOSURE_HULL; HULL_UNIQUE]);;


let CLOSURE_EMPTY = 
prove
 (`closure {} = {}`,


let CLOSURE_UNIV = 
prove
 (`closure(:real^N) = (:real^N)`,


let CLOSURE_UNIONS = 
prove
 (`!f. FINITE f ==> closure(UNIONS f) = UNIONS {closure s | s IN f}`,

  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[UNIONS_0; UNIONS_INSERT; SET_RULE `{f x | x IN {}} = {}`;
     SET_RULE `{f x | x IN a INSERT s} = (f a) INSERT {f x | x IN s}`] THEN
  SIMP_TAC[CLOSURE_EMPTY; CLOSURE_UNION]);;


let CLOSURE_EQ_EMPTY = 
prove
 (`!s. closure s = {} <=> s = {}`,

  GEN_TAC THEN EQ_TAC THEN SIMP_TAC[CLOSURE_EMPTY] THEN
  MATCH_MP_TAC(SET_RULE `s SUBSET t ==> t = {} ==> s = {}`) THEN
  REWRITE_TAC[CLOSURE_SUBSET]);;


let CLOSURE_SUBSET_EQ = 
prove
 (`!s:real^N->bool. closure s SUBSET s <=> closed s`,

  GEN_TAC THEN REWRITE_TAC[GSYM CLOSURE_EQ] THEN
  MP_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN SET_TAC[]);;


let OPEN_INTER_CLOSURE_EQ_EMPTY = 
prove
 (`!s t:real^N->bool.
        open s ==> (s INTER (closure t) = {} <=> s INTER t = {})`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [MP_TAC(ISPEC `t:real^N->bool` CLOSURE_SUBSET) THEN SET_TAC[]; ALL_TAC] THEN
  DISCH_TAC THEN REWRITE_TAC[CLOSURE_INTERIOR] THEN
  MATCH_MP_TAC(SET_RULE `s SUBSET t ==> s INTER (UNIV DIFF t) = {}`) THEN
  ASM_SIMP_TAC[OPEN_SUBSET_INTERIOR] THEN ASM SET_TAC[]);;


let OPEN_INTER_CLOSURE_SUBSET = 
prove
 (`!s t:real^N->bool.
        open s ==> (s INTER (closure t)) SUBSET closure(s INTER t)`,

  REPEAT STRIP_TAC THEN
  SIMP_TAC[SUBSET; IN_INTER; closure; IN_UNION; IN_ELIM_THM] THEN
  X_GEN_TAC `x:real^N` THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  DISJ2_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [open_def]) THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIMPT_APPROACHABLE]) THEN
  DISCH_THEN(MP_TAC o SPEC `min d e`) THEN
  ASM_REWRITE_TAC[REAL_LT_MIN; IN_INTER] THEN
  MATCH_MP_TAC MONO_EXISTS THEN ASM_MESON_TAC[]);;


let CLOSURE_OPEN_INTER_SUPERSET = 
prove
 (`!s t:real^N->bool.
        open s /\ s SUBSET closure t ==> closure(s INTER t) = closure s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  SIMP_TAC[SUBSET_CLOSURE; INTER_SUBSET] THEN
  MATCH_MP_TAC CLOSURE_MINIMAL THEN REWRITE_TAC[CLOSED_CLOSURE] THEN
  W(MP_TAC o PART_MATCH (rand o rand)
    OPEN_INTER_CLOSURE_SUBSET o rand o snd) THEN
  ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] SUBSET_TRANS) THEN ASM SET_TAC[]);;


let CLOSURE_COMPLEMENT = 
prove
 (`!s:real^N->bool. closure(UNIV DIFF s) = UNIV DIFF interior(s)`,

  REWRITE_TAC[SET_RULE `s = UNIV DIFF t <=> UNIV DIFF s = t`] THEN
  REWRITE_TAC[GSYM INTERIOR_CLOSURE]);;


let INTERIOR_COMPLEMENT = 
prove
 (`!s:real^N->bool. interior(UNIV DIFF s) = UNIV DIFF closure(s)`,

  REWRITE_TAC[SET_RULE `s = UNIV DIFF t <=> UNIV DIFF s = t`] THEN
  REWRITE_TAC[GSYM CLOSURE_INTERIOR]);;


let CONNECTED_INTERMEDIATE_CLOSURE = 
prove
 (`!s t:real^N->bool.
        connected s /\ s SUBSET t /\ t SUBSET closure s ==> connected t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[connected; NOT_EXISTS_THM] THEN
  STRIP_TAC THEN
  MAP_EVERY X_GEN_TAC [`u:real^N->bool`; `v:real^N->bool`] THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`u:real^N->bool`; `v:real^N->bool`]) THEN
  ASM_REWRITE_TAC[] THEN ASSUME_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN
  REPLICATE_TAC 2 (CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  REWRITE_TAC[GSYM DE_MORGAN_THM] THEN STRIP_TAC THENL
   [SUBGOAL_THEN `(closure s) SUBSET ((:real^N) DIFF u)` MP_TAC THENL
     [MATCH_MP_TAC CLOSURE_MINIMAL THEN ASM_REWRITE_TAC[GSYM OPEN_CLOSED];
      ALL_TAC];
    SUBGOAL_THEN `(closure s) SUBSET ((:real^N) DIFF v)` MP_TAC THENL
     [MATCH_MP_TAC CLOSURE_MINIMAL THEN ASM_REWRITE_TAC[GSYM OPEN_CLOSED];
      ALL_TAC]] THEN
  ASM SET_TAC[]);;


let CONNECTED_CLOSURE = 
prove
 (`!s:real^N->bool. connected s ==> connected(closure s)`,


let CONNECTED_UNION_STRONG = 
prove
 (`!s t:real^N->bool.
        connected s /\ connected t /\ ~(closure s INTER t = {})
        ==> connected(s UNION t)`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
  DISCH_THEN(X_CHOOSE_TAC `p:real^N`) THEN
  SUBGOAL_THEN `s UNION t = ((p:real^N) INSERT s) UNION t` SUBST1_TAC THENL
   [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC CONNECTED_UNION THEN ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [MATCH_MP_TAC CONNECTED_INTERMEDIATE_CLOSURE THEN
    EXISTS_TAC `s:real^N->bool` THEN ASM_REWRITE_TAC[] THEN
    MP_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN ASM SET_TAC[];
    ASM SET_TAC[]]);;


let INTERIOR_DIFF = 
prove
 (`!s t. interior(s DIFF t) = interior(s) DIFF closure(t)`,

  ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s INTER (UNIV DIFF t)`] THEN
  REWRITE_TAC[INTERIOR_INTER; CLOSURE_INTERIOR] THEN SET_TAC[]);;


let LIMPT_OF_CLOSURE = 
prove
 (`!x:real^N s. x limit_point_of closure s <=> x limit_point_of s`,

  REWRITE_TAC[closure; IN_UNION; IN_ELIM_THM; LIMIT_POINT_UNION] THEN
  REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT `(q ==> p) ==> (p \/ q <=> p)`) THEN
  REWRITE_TAC[LIMPT_OF_LIMPTS]);;


let CLOSED_IN_LIMPT = 
prove
 (`!s t. closed_in (subtopology euclidean t) s <=>
         s SUBSET t /\ !x:real^N. x limit_point_of s /\ x IN t ==> x IN s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_CLOSED] THEN EQ_TAC THENL
   [DISCH_THEN(X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC) THEN
    ASM_SIMP_TAC[IN_INTER] THEN
    ASM_MESON_TAC[CLOSED_LIMPT; LIMPT_SUBSET; INTER_SUBSET];
    STRIP_TAC THEN EXISTS_TAC `closure s :real^N->bool` THEN
    REWRITE_TAC[CLOSED_CLOSURE] THEN REWRITE_TAC[closure] THEN
    ASM SET_TAC[]]);;


let CLOSED_IN_INTER_CLOSURE = 
prove
 (`!s t:real^N->bool.
        closed_in (subtopology euclidean s) t <=> s INTER closure t = t`,

  REWRITE_TAC[closure; CLOSED_IN_LIMPT] THEN SET_TAC[]);;


let INTERIOR_CLOSURE_IDEMP = 
prove
 (`!s:real^N->bool.
        interior(closure(interior(closure s))) = interior(closure s)`,


let CLOSURE_INTERIOR_IDEMP = 
prove
 (`!s:real^N->bool.
        closure(interior(closure(interior s))) = closure(interior s)`,

  GEN_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `s = t <=> UNIV DIFF s = UNIV DIFF t`] THEN
  REWRITE_TAC[GSYM INTERIOR_COMPLEMENT; GSYM CLOSURE_COMPLEMENT] THEN
  REWRITE_TAC[INTERIOR_CLOSURE_IDEMP]);;


let NOWHERE_DENSE_UNION = 
prove
 (`!s t:real^N->bool.
        interior(closure(s UNION t)) = {} <=>
        interior(closure s) = {} /\ interior(closure t) = {}`,


let NOWHERE_DENSE = 
prove
 (`!s:real^N->bool.
        interior(closure s) = {} <=>
        !t. open t /\ ~(t = {})
            ==> ?u. open u /\ ~(u = {}) /\ u SUBSET t /\ u INTER s = {}`,

  GEN_TAC THEN REWRITE_TAC[INTERIOR_EQ_EMPTY_ALT] THEN EQ_TAC THEN
  DISCH_TAC THEN X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THENL
   [EXISTS_TAC `t DIFF closure s:real^N->bool` THEN
    ASM_SIMP_TAC[OPEN_DIFF; CLOSED_CLOSURE] THEN
    MP_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN SET_TAC[];
    FIRST_X_ASSUM(MP_TAC o SPEC `t:real^N->bool`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC) THEN
    MP_TAC(ISPECL [`u:real^N->bool`; `s:real^N->bool`]
        OPEN_INTER_CLOSURE_EQ_EMPTY) THEN
    ASM SET_TAC[]]);;


let INTERIOR_CLOSURE_INTER_OPEN = 
prove
 (`!s t:real^N->bool.
        open s /\ open t
        ==> interior(closure(s INTER t)) =
            interior(closure s) INTER interior(closure t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[SET_RULE
   `u = s INTER t <=> s INTER t SUBSET u /\ u SUBSET s /\ u SUBSET t`] THEN
  SIMP_TAC[SUBSET_INTERIOR; SUBSET_CLOSURE; INTER_SUBSET] THEN
  MATCH_MP_TAC INTERIOR_MAXIMAL THEN SIMP_TAC[OPEN_INTER; OPEN_INTERIOR] THEN
  REWRITE_TAC[SET_RULE `s SUBSET t <=> s INTER (UNIV DIFF t) = {}`;
              GSYM INTERIOR_COMPLEMENT] THEN
  REWRITE_TAC[GSYM INTERIOR_INTER] THEN
  REWRITE_TAC[INTERIOR_EQ_EMPTY] THEN
  X_GEN_TAC `u:real^N->bool` THEN STRIP_TAC THEN
  MP_TAC(ISPECL [`u INTER s:real^N->bool`; `t:real^N->bool`]
        OPEN_INTER_CLOSURE_EQ_EMPTY) THEN
  MP_TAC(ISPECL [`u:real^N->bool`; `s:real^N->bool`]
        OPEN_INTER_CLOSURE_EQ_EMPTY) THEN
  ASM_SIMP_TAC[OPEN_INTER] THEN ASM SET_TAC[]);;


let CLOSURE_INTERIOR_UNION_CLOSED = 
prove
 (`!s t:real^N->bool.
        closed s /\ closed t
        ==> closure(interior(s UNION t)) =
            closure(interior s) UNION closure(interior t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[closed] THEN
  DISCH_THEN(MP_TAC o MATCH_MP INTERIOR_CLOSURE_INTER_OPEN) THEN
  REWRITE_TAC[CLOSURE_COMPLEMENT; INTERIOR_COMPLEMENT;
              SET_RULE `(UNIV DIFF s) INTER (UNIV DIFF t) =
                        UNIV DIFF (s UNION t)`] THEN
  SET_TAC[]);;


let REGULAR_OPEN_INTER = 
prove
 (`!s t:real^N->bool.
        interior(closure s) = s /\ interior(closure t) = t
        ==> interior(closure(s INTER t)) = s INTER t`,


let REGULAR_CLOSED_UNION = 
prove
 (`!s t:real^N->bool.
        closure(interior s) = s /\ closure(interior t) = t
        ==> closure(interior(s UNION t)) = s UNION t`,


let DIFF_CLOSURE_SUBSET = 
prove
 (`!s t:real^N->bool. closure(s) DIFF closure t SUBSET closure(s DIFF t)`,

  REPEAT GEN_TAC THEN
  MP_TAC(ISPECL [`(:real^N) DIFF closure t`; `s:real^N->bool`]
        OPEN_INTER_CLOSURE_SUBSET) THEN
  REWRITE_TAC[SET_RULE `(UNIV DIFF t) INTER s = s DIFF t`] THEN
  REWRITE_TAC[GSYM closed; CLOSED_CLOSURE] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] SUBSET_TRANS) THEN
  MATCH_MP_TAC SUBSET_CLOSURE THEN
  MATCH_MP_TAC(SET_RULE `t SUBSET u ==> s DIFF u SUBSET s DIFF t`) THEN
  REWRITE_TAC[CLOSURE_SUBSET]);;

(* ------------------------------------------------------------------------- *)
(* Frontier (aka boundary).                                                  *)
(* ------------------------------------------------------------------------- *)


let frontier = new_definition
  `frontier s = (closure s) DIFF (interior s)`;;


let FRONTIER_CLOSED = 
prove
 (`!s. closed(frontier s)`,

  SIMP_TAC[frontier; CLOSED_DIFF; CLOSED_CLOSURE; OPEN_INTERIOR]);;


let FRONTIER_CLOSURES = 
prove
 (`!s:real^N->bool. frontier s = (closure s) INTER (closure(UNIV DIFF s))`,

  
let lemma = prove(`s DIFF (UNIV DIFF t) = s INTER t`,SET_TAC[]) in
  REWRITE_TAC[frontier; INTERIOR_CLOSURE; lemma]);;


let FRONTIER_STRADDLE = 
prove
 (`!a:real^N s.
     a IN frontier s <=>
        !e. &0 < e ==> (?x. x IN s /\ dist(a,x) < e) /\
                       (?x. ~(x IN s) /\ dist(a,x) < e)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[FRONTIER_CLOSURES; IN_INTER] THEN
  REWRITE_TAC[closure; IN_UNION; IN_ELIM_THM; limit_point_of;
              IN_UNIV; IN_DIFF] THEN
  ASM_MESON_TAC[IN_BALL; SUBSET; OPEN_CONTAINS_BALL;
                CENTRE_IN_BALL; OPEN_BALL; DIST_REFL]);;


let FRONTIER_SUBSET_CLOSED = 
prove
 (`!s. closed s ==> (frontier s) SUBSET s`,

  MESON_TAC[frontier; CLOSURE_CLOSED; SUBSET_DIFF]);;


let FRONTIER_EMPTY = 
prove
 (`frontier {} = {}`,

  REWRITE_TAC[frontier; CLOSURE_EMPTY; EMPTY_DIFF]);;


let FRONTIER_UNIV = 
prove
 (`frontier(:real^N) = {}`,

  REWRITE_TAC[frontier; CLOSURE_UNIV; INTERIOR_UNIV] THEN SET_TAC[]);;


let FRONTIER_SUBSET_EQ = 
prove
 (`!s:real^N->bool. (frontier s) SUBSET s <=> closed s`,

  GEN_TAC THEN EQ_TAC THEN SIMP_TAC[FRONTIER_SUBSET_CLOSED] THEN
  REWRITE_TAC[frontier] THEN
  DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE
   `s DIFF t SUBSET u ==> t SUBSET u ==> s SUBSET u`)) THEN
  REWRITE_TAC[INTERIOR_SUBSET; CLOSURE_SUBSET_EQ]);;


let FRONTIER_COMPLEMENT = 
prove
 (`!s:real^N->bool. frontier(UNIV DIFF s) = frontier s`,

  REWRITE_TAC[frontier; CLOSURE_COMPLEMENT; INTERIOR_COMPLEMENT] THEN
  SET_TAC[]);;


let FRONTIER_DISJOINT_EQ = 
prove
 (`!s. (frontier s) INTER s = {} <=> open s`,

  ONCE_REWRITE_TAC[GSYM FRONTIER_COMPLEMENT; OPEN_CLOSED] THEN
  REWRITE_TAC[GSYM FRONTIER_SUBSET_EQ] THEN SET_TAC[]);;


let FRONTIER_INTER_SUBSET = 
prove
 (`!s t. frontier(s INTER t) SUBSET frontier(s) UNION frontier(t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[frontier; INTERIOR_INTER] THEN
  MATCH_MP_TAC(SET_RULE
   `cst SUBSET cs INTER ct
    ==> cst DIFF (s INTER t) SUBSET (cs DIFF s) UNION (ct DIFF t)`) THEN
  REWRITE_TAC[CLOSURE_INTER_SUBSET]);;


let FRONTIER_UNION_SUBSET = 
prove
 (`!s t:real^N->bool. frontier(s UNION t) SUBSET frontier s UNION frontier t`,

  ONCE_REWRITE_TAC[GSYM FRONTIER_COMPLEMENT] THEN
  REWRITE_TAC[SET_RULE `u DIFF (s UNION t) = (u DIFF s) INTER (u DIFF t)`] THEN
  REWRITE_TAC[FRONTIER_INTER_SUBSET]);;


let FRONTIER_INTERIORS = 
prove
 (`!s. frontier s = (:real^N) DIFF interior(s) DIFF interior((:real^N) DIFF s)`,

  REWRITE_TAC[frontier; CLOSURE_INTERIOR] THEN SET_TAC[]);;


let FRONTIER_FRONTIER_SUBSET = 
prove
 (`!s:real^N->bool. frontier(frontier s) SUBSET frontier s`,

  GEN_TAC THEN GEN_REWRITE_TAC LAND_CONV [frontier] THEN
  SIMP_TAC[CLOSURE_CLOSED; FRONTIER_CLOSED] THEN SET_TAC[]);;


let INTERIOR_FRONTIER = 
prove
 (`!s:real^N->bool.
        interior(frontier s) = interior(closure s) DIFF closure(interior s)`,

  ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s INTER (UNIV DIFF t)`] THEN
  REWRITE_TAC[GSYM INTERIOR_COMPLEMENT; GSYM INTERIOR_INTER; frontier] THEN
  GEN_TAC THEN AP_TERM_TAC THEN SET_TAC[]);;


let INTERIOR_FRONTIER_EMPTY = 
prove
 (`!s:real^N->bool. open s \/ closed s ==> interior(frontier s) = {}`,

  REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[INTERIOR_FRONTIER] THEN
  ASM_SIMP_TAC[CLOSURE_CLOSED; INTERIOR_OPEN] THEN
  REWRITE_TAC[SET_RULE `s DIFF t = {} <=> s SUBSET t`] THEN
  REWRITE_TAC[INTERIOR_SUBSET; CLOSURE_SUBSET]);;


let FRONTIER_FRONTIER = 
prove
 (`!s:real^N->bool. open s \/ closed s ==> frontier(frontier s) = frontier s`,

  GEN_TAC THEN GEN_REWRITE_TAC (RAND_CONV o LAND_CONV) [frontier] THEN
  SIMP_TAC[INTERIOR_FRONTIER_EMPTY; CLOSURE_CLOSED; FRONTIER_CLOSED] THEN
  REWRITE_TAC[DIFF_EMPTY]);;


let FRONTIER_FRONTIER_FRONTIER = 
prove
 (`!s:real^N->bool. frontier(frontier(frontier s)) = frontier(frontier s)`,


let UNION_FRONTIER = 
prove
 (`!s t:real^N->bool.
        frontier(s) UNION frontier(t) =
        frontier(s UNION t) UNION
        frontier(s INTER t) UNION
        frontier(s) INTER frontier(t)`,

  
let lemma = prove
   (`!s t x. x IN frontier s /\ x IN interior t ==> x IN frontier(s INTER t)`,
    REWRITE_TAC[FRONTIER_STRADDLE; IN_INTER; IN_INTERIOR; SUBSET; IN_BALL] THEN
    REPEAT GEN_TAC THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (X_CHOOSE_TAC `d:real`)) THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `min d e:real`) THEN
    ASM_REWRITE_TAC[REAL_LT_MIN] THEN ASM_MESON_TAC[]) in
  REWRITE_TAC[GSYM SUBSET_ANTISYM_EQ; UNION_SUBSET;
              FRONTIER_UNION_SUBSET; FRONTIER_INTER_SUBSET;
              SET_RULE `s INTER t SUBSET s UNION t`] THEN
  REWRITE_TAC[GSYM UNION_SUBSET] THEN REWRITE_TAC[SUBSET; IN_UNION] THEN
  MATCH_MP_TAC(MESON[]
   `(!s t x. P s x ==> R x s t) /\ (!s t x. R x s t <=> R x t s)
    ==> (!s t x. P s x \/ P t x ==> R x s t)`) THEN
  CONJ_TAC THENL [REPEAT STRIP_TAC; REWRITE_TAC[UNION_COMM; INTER_COMM]] THEN
  ASM_CASES_TAC `(x:real^N) IN frontier t` THEN ASM_REWRITE_TAC[IN_INTER] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE (RAND_CONV o RAND_CONV)
        [FRONTIER_INTERIORS]) THEN
  REWRITE_TAC[DE_MORGAN_THM; IN_DIFF; IN_UNIV] THEN
  GEN_REWRITE_TAC RAND_CONV [DISJ_SYM] THEN MATCH_MP_TAC MONO_OR THEN
  ASM_SIMP_TAC[lemma] THEN
  POP_ASSUM MP_TAC THEN ONCE_REWRITE_TAC[GSYM FRONTIER_COMPLEMENT] THEN
  SIMP_TAC[lemma; SET_RULE
    `UNIV DIFF (s UNION t) = (UNIV DIFF s) INTER (UNIV DIFF t)`]);;


let CONNECTED_INTER_FRONTIER = 
prove
 (`!s t:real^N->bool.
        connected s /\ ~(s INTER t = {}) /\ ~(s DIFF t = {})
        ==> ~(s INTER frontier t = {})`,

  REWRITE_TAC[FRONTIER_INTERIORS] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONNECTED_OPEN_IN]) THEN
  REWRITE_TAC[] THEN MAP_EVERY EXISTS_TAC
   [`s INTER interior t:real^N->bool`;
    `s INTER (interior((:real^N) DIFF t))`] THEN
  SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_INTERIOR] THEN
  MAP_EVERY (MP_TAC o C ISPEC INTERIOR_SUBSET)
   [`t:real^N->bool`; `(:real^N) DIFF t`] THEN
  ASM SET_TAC[]);;


let INTERIOR_CLOSED_EQ_EMPTY_AS_FRONTIER = 
prove
 (`!s:real^N->bool.
        closed s /\ interior s = {} <=> ?t. open t /\ s = frontier t`,

  GEN_TAC THEN EQ_TAC THEN STRIP_TAC THENL
   [EXISTS_TAC `(:real^N) DIFF s` THEN
    ASM_SIMP_TAC[OPEN_DIFF; OPEN_UNIV; FRONTIER_COMPLEMENT] THEN
    ASM_SIMP_TAC[frontier; CLOSURE_CLOSED; DIFF_EMPTY];
    ASM_SIMP_TAC[FRONTIER_CLOSED; INTERIOR_FRONTIER_EMPTY]]);;


let FRONTIER_UNION = 
prove
 (`!s t:real^N->bool.
        closure s INTER closure t = {}
        ==> frontier(s UNION t) = frontier(s) UNION frontier(t)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SUBSET_ANTISYM THEN REWRITE_TAC[FRONTIER_UNION_SUBSET] THEN
  GEN_REWRITE_TAC RAND_CONV [frontier] THEN
  REWRITE_TAC[CLOSURE_UNION] THEN MATCH_MP_TAC(SET_RULE
   `(fs SUBSET cs /\ ft SUBSET ct) /\ k INTER fs = {} /\ k INTER ft = {}
    ==> (fs UNION ft) SUBSET (cs UNION ct) DIFF k`) THEN
  CONJ_TAC THENL [REWRITE_TAC[frontier] THEN SET_TAC[]; ALL_TAC] THEN
  CONJ_TAC THENL
   [ALL_TAC;
    ONCE_REWRITE_TAC[UNION_COMM] THEN
    RULE_ASSUM_TAC(ONCE_REWRITE_RULE[INTER_COMM])] THEN
  FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (SET_RULE
   `s INTER t = {} ==> s' SUBSET s /\ s' INTER u INTER (UNIV DIFF t) = {}
      ==> u INTER s' = {}`)) THEN
  REWRITE_TAC[frontier; SUBSET_DIFF; GSYM INTERIOR_COMPLEMENT] THEN
  REWRITE_TAC[GSYM INTERIOR_INTER; SET_RULE
   `(s UNION t) INTER (UNIV DIFF t) = s DIFF t`] THEN
  MATCH_MP_TAC(SET_RULE
    `ti SUBSET si ==> (c DIFF si) INTER ti = {}`) THEN
  SIMP_TAC[SUBSET_INTERIOR; SUBSET_DIFF]);;


let CLOSURE_UNION_FRONTIER = 
prove
 (`!s:real^N->bool. closure s = s UNION frontier s`,

  GEN_TAC THEN REWRITE_TAC[frontier] THEN
  MP_TAC(ISPEC `s:real^N->bool` INTERIOR_SUBSET) THEN
  MP_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN
  SET_TAC[]);;


let FRONTIER_INTERIOR_SUBSET = 
prove
 (`!s:real^N->bool. frontier(interior s) SUBSET frontier s`,

  GEN_TAC THEN REWRITE_TAC[frontier; INTERIOR_INTERIOR] THEN
  MATCH_MP_TAC(SET_RULE `s SUBSET t ==> s DIFF u SUBSET t DIFF u`) THEN
  SIMP_TAC[SUBSET_CLOSURE; INTERIOR_SUBSET]);;


let FRONTIER_CLOSURE_SUBSET = 
prove
 (`!s:real^N->bool. frontier(closure s) SUBSET frontier s`,

  GEN_TAC THEN REWRITE_TAC[frontier; CLOSURE_CLOSURE] THEN
  MATCH_MP_TAC(SET_RULE `s SUBSET t ==> u DIFF t SUBSET u DIFF s`) THEN
  SIMP_TAC[SUBSET_INTERIOR; CLOSURE_SUBSET]);;


let SET_DIFF_FRONTIER = 
prove
 (`!s:real^N->bool. s DIFF frontier s = interior s`,

  GEN_TAC THEN REWRITE_TAC[frontier] THEN
  MP_TAC(ISPEC `s:real^N->bool` INTERIOR_SUBSET) THEN
  MP_TAC(ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN
  SET_TAC[]);;


let FRONTIER_INTER_SUBSET_INTER = 
prove
 (`!s t:real^N->bool.
        frontier(s INTER t) SUBSET closure s INTER frontier t UNION
                                   frontier s INTER closure t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[frontier; INTERIOR_INTER] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`]
        CLOSURE_INTER_SUBSET) THEN
  SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* A variant of nets (slightly non-standard but good for our purposes).      *)
(* ------------------------------------------------------------------------- *)

let net_tybij = new_type_definition "net" ("mk_net","netord")
 (prove
   (`?g:A->A->bool. !x y. (!z. g z x ==> g z y) \/ (!z. g z y ==> g z x)`,
    EXISTS_TAC `\x:A y:A. F` THEN REWRITE_TAC[]));;


let NET = 
prove
 (`!n x y. (!z. netord n z x ==> netord n z y) \/
           (!z. netord n z y ==> netord n z x)`,

   REWRITE_TAC[net_tybij; ETA_AX]);;


let OLDNET = 
prove
 (`!n x y. netord n x x /\ netord n y y
           ==> ?z. netord n z z /\
                   !w. netord n w z ==> netord n w x /\ netord n w y`,

  MESON_TAC[NET]);;


let NET_DILEMMA = 
prove
 (`!net. (?a. (?x. netord net x a) /\ (!x. netord net x a ==> P x)) /\
         (?b. (?x. netord net x b) /\ (!x. netord net x b ==> Q x))
         ==> ?c. (?x. netord net x c) /\ (!x. netord net x c ==> P x /\ Q x)`,

  MESON_TAC[NET]);;

(* ------------------------------------------------------------------------- *)
(* Common nets and the "within" modifier for nets.                           *)
(* ------------------------------------------------------------------------- *)

parse_as_infix("within",(14,"right"));;
parse_as_infix("in_direction",(14,"right"));;


let at = new_definition
  `at a = mk_net(\x y. &0 < dist(x,a) /\ dist(x,a) <= dist(y,a))`;;


let at_infinity = new_definition
  `at_infinity = mk_net(\x y. norm(x) >= norm(y))`;;


let at_posinfinity = new_definition
  `at_posinfinity = mk_net(\x y:real. x >= y)`;;


let at_neginfinity = new_definition
  `at_neginfinity = mk_net(\x y:real. x <= y)`;;


let sequentially = new_definition
  `sequentially = mk_net(\m:num n. m >= n)`;;


let within = new_definition
  `net within s = mk_net(\x y. netord net x y /\ x IN s)`;;


let in_direction = new_definition
  `a in_direction v = (at a) within {b | ?c. &0 <= c /\ (b - a = c % v)}`;;

(* ------------------------------------------------------------------------- *)
(* Prove that they are all nets.                                             *)
(* ------------------------------------------------------------------------- *)

let NET_PROVE_TAC[def] =
  REWRITE_TAC[GSYM FUN_EQ_THM; def] THEN
  REWRITE_TAC[ETA_AX] THEN
  ASM_SIMP_TAC[GSYM(CONJUNCT2 net_tybij)];;


let AT = 
prove
 (`!a:real^N x y.
        netord(at a) x y <=> &0 < dist(x,a) /\ dist(x,a) <= dist(y,a)`,

  GEN_TAC THEN NET_PROVE_TAC[at] THEN
  MESON_TAC[REAL_LE_TOTAL; REAL_LE_REFL; REAL_LE_TRANS; REAL_LET_TRANS]);;


let AT_INFINITY = 
prove
 (`!x y. netord at_infinity x y <=> norm(x) >= norm(y)`,

  NET_PROVE_TAC[at_infinity] THEN
  REWRITE_TAC[real_ge; REAL_LE_REFL] THEN
  MESON_TAC[REAL_LE_TOTAL; REAL_LE_REFL; REAL_LE_TRANS]);;


let AT_POSINFINITY = 
prove
 (`!x y. netord at_posinfinity x y <=> x >= y`,

  NET_PROVE_TAC[at_posinfinity] THEN
  REWRITE_TAC[real_ge; REAL_LE_REFL] THEN
  MESON_TAC[REAL_LE_TOTAL; REAL_LE_REFL; REAL_LE_TRANS]);;


let AT_NEGINFINITY = 
prove
 (`!x y. netord at_neginfinity x y <=> x <= y`,

  NET_PROVE_TAC[at_neginfinity] THEN
  REWRITE_TAC[real_ge; REAL_LE_REFL] THEN
  MESON_TAC[REAL_LE_TOTAL; REAL_LE_REFL; REAL_LE_TRANS]);;


let SEQUENTIALLY = 
prove
 (`!m n. netord sequentially m n <=> m >= n`,

  NET_PROVE_TAC[sequentially] THEN REWRITE_TAC[GE; LE_REFL] THEN
  MESON_TAC[LE_CASES; LE_REFL; LE_TRANS]);;


let WITHIN = 
prove
 (`!n s x y. netord(n within s) x y <=> netord n x y /\ x IN s`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[within; GSYM FUN_EQ_THM] THEN
  REWRITE_TAC[GSYM(CONJUNCT2 net_tybij); ETA_AX] THEN
  MESON_TAC[NET]);;


let IN_DIRECTION = 
prove
 (`!a v x y. netord(a in_direction v) x y <=>
                &0 < dist(x,a) /\ dist(x,a) <= dist(y,a) /\
                 ?c. &0 <= c /\ (x - a = c % v)`,


let WITHIN_UNIV = 
prove
 (`!x:real^N. at x within UNIV = at x`,

  REWRITE_TAC[within; at; IN_UNIV] THEN REWRITE_TAC[ETA_AX; net_tybij]);;


let WITHIN_WITHIN = 
prove
 (`!net s t. (net within s) within t = net within (s INTER t)`,

  ONCE_REWRITE_TAC[within] THEN
  REWRITE_TAC[WITHIN; IN_INTER; GSYM CONJ_ASSOC]);;

(* ------------------------------------------------------------------------- *)
(* Identify trivial limits, where we can't approach arbitrarily closely.     *)
(* ------------------------------------------------------------------------- *)


let trivial_limit = new_definition
  `trivial_limit net <=>
     (!a:A b. a = b) \/
     ?a:A b. ~(a = b) /\ !x. ~(netord(net) x a) /\ ~(netord(net) x b)`;;


let TRIVIAL_LIMIT_WITHIN = 
prove
 (`!a:real^N. trivial_limit (at a within s) <=> ~(a limit_point_of s)`,

  REWRITE_TAC[trivial_limit; LIMPT_APPROACHABLE_LE; WITHIN; AT; DIST_NZ] THEN
  REPEAT GEN_TAC THEN EQ_TAC THENL
   [DISCH_THEN(DISJ_CASES_THEN MP_TAC) THENL
     [MESON_TAC[REAL_LT_01; REAL_LT_REFL; VECTOR_CHOOSE_DIST;
                DIST_REFL; REAL_LT_IMP_LE];
      DISCH_THEN(X_CHOOSE_THEN `b:real^N` (X_CHOOSE_THEN `c:real^N`
        STRIP_ASSUME_TAC)) THEN
      SUBGOAL_THEN `&0 < dist(a,b:real^N) \/ &0 < dist(a,c:real^N)` MP_TAC THEN
      ASM_MESON_TAC[DIST_TRIANGLE; DIST_SYM; GSYM DIST_NZ; GSYM DIST_EQ_0;
                    REAL_ARITH `x <= &0 + &0 ==> ~(&0 < x)`]];
    REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN DISJ2_TAC THEN
    EXISTS_TAC `a:real^N` THEN
    SUBGOAL_THEN `?b:real^N. dist(a,b) = e` MP_TAC THENL
     [ASM_SIMP_TAC[VECTOR_CHOOSE_DIST; REAL_LT_IMP_LE]; ALL_TAC] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:real^N` THEN
    DISCH_THEN(SUBST_ALL_TAC o SYM) THEN
    ASM_MESON_TAC[REAL_NOT_LE; DIST_REFL; DIST_NZ; DIST_SYM]]);;


let TRIVIAL_LIMIT_AT = 
prove
 (`!a. ~(trivial_limit (at a))`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[TRIVIAL_LIMIT_WITHIN; LIMPT_UNIV]);;


let TRIVIAL_LIMIT_AT_INFINITY = 
prove
 (`~(trivial_limit at_infinity)`,


let TRIVIAL_LIMIT_AT_POSINFINITY = 
prove
 (`~(trivial_limit at_posinfinity)`,

  REWRITE_TAC[trivial_limit; AT_POSINFINITY; DE_MORGAN_THM] THEN
  CONJ_TAC THENL
   [DISCH_THEN(MP_TAC o SPECL [`&0`; `&1`]) THEN REAL_ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[DE_MORGAN_THM; NOT_EXISTS_THM; real_ge; REAL_NOT_LE] THEN
  MESON_TAC[REAL_LT_TOTAL; REAL_LT_ANTISYM]);;


let TRIVIAL_LIMIT_AT_NEGINFINITY = 
prove
 (`~(trivial_limit at_neginfinity)`,

  REWRITE_TAC[trivial_limit; AT_NEGINFINITY; DE_MORGAN_THM] THEN
  CONJ_TAC THENL
   [DISCH_THEN(MP_TAC o SPECL [`&0`; `&1`]) THEN REAL_ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[DE_MORGAN_THM; NOT_EXISTS_THM; real_ge; REAL_NOT_LE] THEN
  MESON_TAC[REAL_LT_TOTAL; REAL_LT_ANTISYM]);;


let TRIVIAL_LIMIT_SEQUENTIALLY = 
prove
 (`~(trivial_limit sequentially)`,

  REWRITE_TAC[trivial_limit; SEQUENTIALLY] THEN
  MESON_TAC[GE_REFL; NOT_SUC]);;


let LIM_WITHIN_CLOSED_TRIVIAL = 
prove
 (`!a s. closed s /\ ~(a IN s) ==> trivial_limit (at a within s)`,

  REWRITE_TAC[TRIVIAL_LIMIT_WITHIN] THEN MESON_TAC[CLOSED_LIMPT]);;


let NONTRIVIAL_LIMIT_WITHIN = 
prove
 (`!net s. trivial_limit net ==> trivial_limit(net within s)`,

  REWRITE_TAC[trivial_limit; WITHIN] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Some property holds "sufficiently close" to the limit point.              *)
(* ------------------------------------------------------------------------- *)


let eventually = new_definition
 `eventually p net <=>
        trivial_limit net \/
        ?y. (?x. netord net x y) /\ (!x. netord net x y ==> p x)`;;


let EVENTUALLY_HAPPENS = 
prove
 (`!net p. eventually p net ==> trivial_limit net \/ ?x. p x`,

  REWRITE_TAC[eventually] THEN MESON_TAC[]);;


let EVENTUALLY_WITHIN_LE = 
prove
 (`!s a:real^M p.
     eventually p (at a within s) <=>
        ?d. &0 < d /\ !x. x IN s /\ &0 < dist(x,a) /\ dist(x,a) <= d ==> p(x)`,

  REWRITE_TAC[eventually; AT; WITHIN; TRIVIAL_LIMIT_WITHIN] THEN
  REWRITE_TAC[LIMPT_APPROACHABLE_LE; DIST_NZ] THEN
  REPEAT GEN_TAC THEN EQ_TAC THENL [MESON_TAC[REAL_LTE_TRANS]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC(TAUT `(a ==> b) ==> ~a \/ b`) THEN DISCH_TAC THEN
  SUBGOAL_THEN `?b:real^M. dist(a,b) = d` MP_TAC THENL
   [ASM_SIMP_TAC[VECTOR_CHOOSE_DIST; REAL_LT_IMP_LE]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:real^M` THEN
  DISCH_THEN(SUBST_ALL_TAC o SYM) THEN
  ASM_MESON_TAC[REAL_NOT_LE; DIST_REFL; DIST_NZ; DIST_SYM]);;


let EVENTUALLY_WITHIN = 
prove
 (`!s a:real^M p.
     eventually p (at a within s) <=>
        ?d. &0 < d /\ !x. x IN s /\ &0 < dist(x,a) /\ dist(x,a) < d ==> p(x)`,

  REWRITE_TAC[EVENTUALLY_WITHIN_LE] THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c ==> d <=> c ==> a /\ b ==> d`] THEN
  REWRITE_TAC[APPROACHABLE_LT_LE]);;


let EVENTUALLY_AT = 
prove
 (`!a p. eventually p (at a) <=>
         ?d. &0 < d /\ !x. &0 < dist(x,a) /\ dist(x,a) < d ==> p(x)`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[EVENTUALLY_WITHIN; IN_UNIV]);;


let EVENTUALLY_SEQUENTIALLY = 
prove
 (`!p. eventually p sequentially <=> ?N. !n. N <= n ==> p n`,

  REWRITE_TAC[eventually; SEQUENTIALLY; GE; LE_REFL;
    TRIVIAL_LIMIT_SEQUENTIALLY] THEN  MESON_TAC[LE_REFL]);;


let EVENTUALLY_AT_INFINITY = 
prove
 (`!p. eventually p at_infinity <=> ?b. !x. norm(x) >= b ==> p x`,

  REWRITE_TAC[eventually; AT_INFINITY; TRIVIAL_LIMIT_AT_INFINITY] THEN
  REPEAT GEN_TAC THEN EQ_TAC THENL [MESON_TAC[REAL_LE_REFL]; ALL_TAC] THEN
  MESON_TAC[real_ge; REAL_LE_REFL; VECTOR_CHOOSE_SIZE;
    REAL_ARITH `&0 <= b \/ (!x. x >= &0 ==> x >= b)`]);;


let EVENTUALLY_AT_POSINFINITY = 
prove
 (`!p. eventually p at_posinfinity <=> ?b. !x. x >= b ==> p x`,

  REWRITE_TAC[eventually; TRIVIAL_LIMIT_AT_POSINFINITY; AT_POSINFINITY] THEN
  MESON_TAC[REAL_ARITH `x >= x`]);;


let EVENTUALLY_AT_NEGINFINITY = 
prove
 (`!p. eventually p at_neginfinity <=> ?b. !x. x <= b ==> p x`,

  REWRITE_TAC[eventually; TRIVIAL_LIMIT_AT_NEGINFINITY; AT_NEGINFINITY] THEN
  MESON_TAC[REAL_LE_REFL]);;


let EVENTUALLY_AT_INFINITY_POS = 
prove
 (`!p:real^N->bool.
        eventually p at_infinity <=> ?b. &0 < b /\ !x. norm x >= b ==> p x`,

  GEN_TAC THEN REWRITE_TAC[EVENTUALLY_AT_INFINITY; real_ge] THEN
  MESON_TAC[REAL_ARITH `&0 < abs b + &1 /\ (abs b + &1 <= x ==> b <= x)`]);;


let ALWAYS_EVENTUALLY = 
prove
 (`(!x. p x) ==> eventually p net`,

  REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[eventually; trivial_limit] THEN
  MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Combining theorems for "eventually".                                      *)
(* ------------------------------------------------------------------------- *)


let EVENTUALLY_AND = 
prove
 (`!net:(A net) p q.
        eventually (\x. p x /\ q x) net <=>
        eventually p net /\ eventually q net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[eventually] THEN
  ASM_CASES_TAC `trivial_limit(net:(A net))` THEN ASM_REWRITE_TAC[] THEN
  EQ_TAC THEN SIMP_TAC[NET_DILEMMA] THEN MESON_TAC[]);;


let EVENTUALLY_MONO = 
prove
 (`!net:(A net) p q.
        (!x. p x ==> q x) /\ eventually p net
        ==> eventually q net`,

  REWRITE_TAC[eventually] THEN MESON_TAC[]);;


let EVENTUALLY_MP = 
prove
 (`!net:(A net) p q.
        eventually (\x. p x ==> q x) net /\ eventually p net
        ==> eventually q net`,

  REWRITE_TAC[GSYM EVENTUALLY_AND] THEN
  REWRITE_TAC[eventually] THEN MESON_TAC[]);;


let EVENTUALLY_FALSE = 
prove
 (`!net. eventually (\x. F) net <=> trivial_limit net`,

  REWRITE_TAC[eventually] THEN MESON_TAC[]);;


let EVENTUALLY_TRUE = 
prove
 (`!net. eventually (\x. T) net <=> T`,

  REWRITE_TAC[eventually; trivial_limit] THEN MESON_TAC[]);;


let NOT_EVENTUALLY = 
prove
 (`!net p. (!x. ~(p x)) /\ ~(trivial_limit net) ==> ~(eventually p net)`,

  REWRITE_TAC[eventually] THEN MESON_TAC[]);;


let EVENTUALLY_FORALL = 
prove
 (`!net:(A net) p s:B->bool.
        FINITE s /\ ~(s = {})
        ==> (eventually (\x. !a. a IN s ==> p a x) net <=>
             !a. a IN s ==> eventually (p a) net)`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[FORALL_IN_INSERT; EVENTUALLY_AND; ETA_AX] THEN
  MAP_EVERY X_GEN_TAC [`b:B`; `t:B->bool`] THEN
  ASM_CASES_TAC `t:B->bool = {}` THEN
  ASM_SIMP_TAC[NOT_IN_EMPTY; EVENTUALLY_TRUE]);;


let FORALL_EVENTUALLY = 
prove
 (`!net:(A net) p s:B->bool.
        FINITE s /\ ~(s = {})
        ==> ((!a. a IN s ==> eventually (p a) net) <=>
             eventually (\x. !a. a IN s ==> p a x) net)`,

  SIMP_TAC[EVENTUALLY_FORALL]);;

(* ------------------------------------------------------------------------- *)
(* Limits, defined as vacuously true when the limit is trivial.              *)
(* ------------------------------------------------------------------------- *)

parse_as_infix("-->",(12,"right"));;


let tendsto = new_definition
  `(f --> l) net <=> !e. &0 < e ==> eventually (\x. dist(f(x),l) < e) net`;;


let lim = new_definition
 `lim net f = @l. (f --> l) net`;;


let LIM = 
prove
 (`(f --> l) net <=>
        trivial_limit net \/
        !e. &0 < e ==> ?y. (?x. netord(net) x y) /\
                           !x. netord(net) x y ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; eventually] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Show that they yield usual definitions in the various cases.              *)
(* ------------------------------------------------------------------------- *)


let LIM_WITHIN_LE = 
prove
 (`!f:real^M->real^N l a s.
        (f --> l)(at a within s) <=>
           !e. &0 < e ==> ?d. &0 < d /\
                              !x. x IN s /\ &0 < dist(x,a) /\ dist(x,a) <= d
                                   ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_WITHIN_LE]);;


let LIM_WITHIN = 
prove
 (`!f:real^M->real^N l a s.
      (f --> l) (at a within s) <=>
        !e. &0 < e
            ==> ?d. &0 < d /\
                    !x. x IN s /\ &0 < dist(x,a) /\ dist(x,a) < d
                    ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_WITHIN] THEN MESON_TAC[]);;


let LIM_AT_LE = 
prove
 (`!f l a. (f --> l) (at a) <=>
           !e. &0 < e
               ==> ?d. &0 < d /\
                       !x. &0 < dist(x,a) /\ dist(x,a) <= d
                           ==> dist (f x,l) < e`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[LIM_WITHIN_LE; IN_UNIV]);;


let LIM_AT = 
prove
 (`!f l:real^N a:real^M.
      (f --> l) (at a) <=>
              !e. &0 < e
                  ==> ?d. &0 < d /\ !x. &0 < dist(x,a) /\ dist(x,a) < d
                          ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_AT] THEN MESON_TAC[]);;


let LIM_AT_INFINITY = 
prove
 (`!f l. (f --> l) at_infinity <=>
               !e. &0 < e ==> ?b. !x. norm(x) >= b ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_AT_INFINITY] THEN MESON_TAC[]);;


let LIM_AT_INFINITY_POS = 
prove
 (`!f l. (f --> l) at_infinity <=>
         !e. &0 < e ==> ?b. &0 < b /\ !x. norm x >= b ==> dist(f x,l) < e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM_AT_INFINITY] THEN
  MESON_TAC[REAL_ARITH `&0 < abs b + &1 /\ (x >= abs b + &1 ==> x >= b)`]);;


let LIM_AT_POSINFINITY = 
prove
 (`!f l. (f --> l) at_posinfinity <=>
               !e. &0 < e ==> ?b. !x. x >= b ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_AT_POSINFINITY] THEN MESON_TAC[]);;


let LIM_AT_NEGINFINITY = 
prove
 (`!f l. (f --> l) at_neginfinity <=>
               !e. &0 < e ==> ?b. !x. x <= b ==> dist(f(x),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_AT_NEGINFINITY] THEN MESON_TAC[]);;


let LIM_SEQUENTIALLY = 
prove
 (`!s l. (s --> l) sequentially <=>
          !e. &0 < e ==> ?N. !n. N <= n ==> dist(s(n),l) < e`,

  REWRITE_TAC[tendsto; EVENTUALLY_SEQUENTIALLY] THEN MESON_TAC[]);;


let LIM_EVENTUALLY = 
prove
 (`!net f l. eventually (\x. f x = l) net ==> (f --> l) net`,

  REWRITE_TAC[eventually; LIM] THEN MESON_TAC[DIST_REFL]);;


let LIM_POSINFINITY_SEQUENTIALLY = 
prove
 (`!f l. (f --> l) at_posinfinity ==> ((\n. f(&n)) --> l) sequentially`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[LIM_AT_POSINFINITY; LIM_SEQUENTIALLY] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e:real`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_TAC `B:real`) THEN
  MP_TAC(ISPEC `B:real` REAL_ARCH_SIMPLE) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM REAL_OF_NUM_LE]) THEN ASM_REAL_ARITH_TAC);;


let LIM_INFINITY_POSINFINITY_LIFT = 
prove
 (`!f l:real^N. (f --> l) at_infinity ==> ((f o lift) --> l) at_posinfinity`,

  REWRITE_TAC[LIM_AT_INFINITY; LIM_AT_POSINFINITY; o_THM] THEN
  REWRITE_TAC[FORALL_DROP; NORM_REAL; GSYM drop; LIFT_DROP] THEN
  MESON_TAC[REAL_ARITH `x >= b ==> abs(x) >= b`]);;

(* ------------------------------------------------------------------------- *)
(* The expected monotonicity property.                                       *)
(* ------------------------------------------------------------------------- *)


let LIM_WITHIN_EMPTY = 
prove
 (`!f l x. (f --> l) (at x within {})`,

  REWRITE_TAC[LIM_WITHIN; NOT_IN_EMPTY] THEN MESON_TAC[REAL_LT_01]);;


let LIM_WITHIN_SUBSET = 
prove
 (`!f l a s.
    (f --> l) (at a within s) /\ t SUBSET s ==> (f --> l) (at a within t)`,

  REWRITE_TAC[LIM_WITHIN; SUBSET] THEN MESON_TAC[]);;


let LIM_UNION = 
prove
 (`!f x l s t.
        (f --> l) (at x within s) /\ (f --> l) (at x within t)
        ==> (f --> l) (at x within (s UNION t))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM_WITHIN; IN_UNION] THEN
  REWRITE_TAC[AND_FORALL_THM] THEN MATCH_MP_TAC MONO_FORALL THEN
  X_GEN_TAC `e:real` THEN ASM_CASES_TAC `&0 < e` THEN ASM_SIMP_TAC[] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_TAC `d1:real`) (X_CHOOSE_TAC `d2:real`)) THEN
  EXISTS_TAC `min d1 d2` THEN ASM_MESON_TAC[REAL_LT_MIN]);;


let LIM_UNION_UNIV = 
prove
 (`!f x l s t.
        (f --> l) (at x within s) /\ (f --> l) (at x within t) /\
        s UNION t = (:real^N)
        ==> (f --> l) (at x)`,

  MESON_TAC[LIM_UNION; WITHIN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Composition of limits.                                                    *)
(* ------------------------------------------------------------------------- *)


let LIM_COMPOSE_WITHIN = 
prove
 (`!net f:A->real^N g:real^N->real^P s y z.
    (f --> y) net /\
    eventually (\w. f w IN s /\ (f w = y ==> g y = z)) net /\
    (g --> z) (at y within s)
    ==> ((g o f) --> z) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto; CONJ_ASSOC] THEN
  ONCE_REWRITE_TAC[LEFT_AND_FORALL_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[EVENTUALLY_WITHIN; GSYM DIST_NZ; o_DEF] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `d:real`) THEN
  ASM_REWRITE_TAC[GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  ASM_MESON_TAC[DIST_REFL]);;


let LIM_COMPOSE_AT = 
prove
 (`!net f:A->real^N g:real^N->real^P y z.
    (f --> y) net /\
    eventually (\w. f w = y ==> g y = z) net /\
    (g --> z) (at y)
    ==> ((g o f) --> z) net`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`net:(A)net`; `f:A->real^N`; `g:real^N->real^P`;
                 `(:real^N)`; `y:real^N`; `z:real^P`]
        LIM_COMPOSE_WITHIN) THEN
  ASM_REWRITE_TAC[IN_UNIV; WITHIN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Interrelations between restricted and unrestricted limits.                *)
(* ------------------------------------------------------------------------- *)


let LIM_AT_WITHIN = 
prove
 (`!f l a s. (f --> l)(at a) ==> (f --> l)(at a within s)`,

  REWRITE_TAC[LIM_AT; LIM_WITHIN] THEN MESON_TAC[]);;


let LIM_WITHIN_OPEN = 
prove
 (`!f l a:real^M s.
     a IN s /\ open s ==> ((f --> l)(at a within s) <=> (f --> l)(at a))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN SIMP_TAC[LIM_AT_WITHIN] THEN
  REWRITE_TAC[LIM_AT; LIM_WITHIN] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
   DISCH_THEN(X_CHOOSE_THEN `d1:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `a:real^M` o GEN_REWRITE_RULE I [open_def]) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `d2:real` STRIP_ASSUME_TAC) THEN
  MP_TAC(SPECL [`d1:real`; `d2:real`] REAL_DOWN2) THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[REAL_LT_TRANS]);;

(* ------------------------------------------------------------------------- *)
(* More limit point characterizations.                                       *)
(* ------------------------------------------------------------------------- *)


let LIMPT_SEQUENTIAL_INJ = 
prove
 (`!x:real^N s.
      x limit_point_of s <=>
             ?f. (!n. f(n) IN (s DELETE x)) /\
                 (!m n. f m = f n <=> m = n) /\
                 (f --> x) sequentially`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[LIMPT_APPROACHABLE; LIM_SEQUENTIALLY; IN_DELETE] THEN
  EQ_TAC THENL [ALL_TAC; MESON_TAC[GE; LE_REFL]] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `y:real->real^N` THEN DISCH_TAC THEN
  (STRIP_ASSUME_TAC o  prove_recursive_functions_exist num_RECURSION)
   `(z 0 = y (&1)) /\
    (!n. z (SUC n):real^N = y(min (inv(&2 pow (SUC n))) (dist(z n,x))))` THEN
  EXISTS_TAC `z:num->real^N` THEN
  SUBGOAL_THEN
   `!n. z(n) IN s /\ ~(z n:real^N = x) /\ dist(z n,x) < inv(&2 pow n)`
  ASSUME_TAC THENL
   [INDUCT_TAC THEN ASM_REWRITE_TAC[] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
    ASM_SIMP_TAC[REAL_LT_01] THEN FIRST_X_ASSUM(MP_TAC o SPEC
     `min (inv(&2 pow (SUC n))) (dist(z n:real^N,x))`) THEN
    ASM_SIMP_TAC[REAL_LT_MIN; REAL_LT_INV_EQ; REAL_LT_POW2; DIST_POS_LT];
    ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
     [MATCH_MP_TAC WLOG_LT THEN REWRITE_TAC[EQ_SYM_EQ] THEN
      SUBGOAL_THEN `!m n:num. m < n ==> dist(z n:real^N,x) < dist(z m,x)`
       (fun th -> MESON_TAC[th; REAL_LT_REFL; LT_REFL]) THEN
      MATCH_MP_TAC TRANSITIVE_STEPWISE_LT THEN
      CONJ_TAC THENL [REAL_ARITH_TAC; GEN_TAC THEN ASM_REWRITE_TAC[]] THEN
      FIRST_X_ASSUM(MP_TAC o SPEC
       `min (inv(&2 pow (SUC n))) (dist(z n:real^N,x))`) THEN
      ASM_SIMP_TAC[REAL_LT_MIN; REAL_LT_INV_EQ; REAL_LT_POW2; DIST_POS_LT];
      X_GEN_TAC `e:real` THEN DISCH_TAC THEN
      MP_TAC(ISPECL [`inv(&2)`; `e:real`] REAL_ARCH_POW_INV) THEN
      ANTS_TAC THENL [ASM_REAL_ARITH_TAC; MATCH_MP_TAC MONO_EXISTS] THEN
      X_GEN_TAC `N:num` THEN REWRITE_TAC[REAL_POW_INV] THEN DISCH_TAC THEN
      X_GEN_TAC `n:num` THEN DISCH_TAC THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT]
        REAL_LT_TRANS)) THEN
      MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `inv(&2 pow n)` THEN
      ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_INV2 THEN
      ASM_REWRITE_TAC[REAL_LT_POW2] THEN MATCH_MP_TAC REAL_POW_MONO THEN
      REWRITE_TAC[REAL_OF_NUM_LE] THEN ASM_ARITH_TAC]]);;


let LIMPT_SEQUENTIAL = 
prove
 (`!x:real^N s.
      x limit_point_of s <=>
             ?f. (!n. f(n) IN (s DELETE x)) /\ (f --> x) sequentially`,

  REPEAT GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[LIMPT_SEQUENTIAL_INJ] THEN MESON_TAC[];
    REWRITE_TAC[LIMPT_APPROACHABLE; LIM_SEQUENTIALLY; IN_DELETE] THEN
    MESON_TAC[GE; LE_REFL]]);;

let [LIMPT_INFINITE_OPEN; LIMPT_INFINITE_BALL; LIMPT_INFINITE_CBALL] =
    (CONJUNCTS o prove)
 (`(!s x:real^N.
        x limit_point_of s <=> !t. x IN t /\ open t ==> INFINITE(s INTER t)) /\
   (!s x:real^N.
        x limit_point_of s <=> !e. &0 < e ==> INFINITE(s INTER ball(x,e))) /\
   (!s x:real^N.
        x limit_point_of s <=> !e. &0 < e ==> INFINITE(s INTER cball(x,e)))`,
  REWRITE_TAC[AND_FORALL_THM] THEN REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT
   `(q ==> p) /\ (r ==> s) /\ (s ==> q) /\ (p ==> r)
    ==> (p <=> q) /\ (p <=> r) /\ (p <=> s)`) THEN
  REPEAT CONJ_TAC THENL
   [REWRITE_TAC[limit_point_of; INFINITE; SET_RULE
     `(?y. ~(y = x) /\ y IN s /\ y IN t) <=> ~(s INTER t SUBSET {x})`] THEN
    MESON_TAC[FINITE_SUBSET; FINITE_SING];
    MESON_TAC[INFINITE_SUPERSET; BALL_SUBSET_CBALL;
              SET_RULE `t SUBSET u ==> s INTER t SUBSET s INTER u`];
    MESON_TAC[INFINITE_SUPERSET; OPEN_CONTAINS_CBALL;
              SET_RULE `t SUBSET u ==> s INTER t SUBSET s INTER u`];
    REWRITE_TAC[LIMPT_SEQUENTIAL_INJ; IN_DELETE; FORALL_AND_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `f:num->real^N` STRIP_ASSUME_TAC) THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIM_SEQUENTIALLY]) THEN
    DISCH_THEN(MP_TAC o SPEC `e:real`) THEN
    ASM_REWRITE_TAC[GSYM(ONCE_REWRITE_RULE[DIST_SYM] IN_BALL)] THEN
    DISCH_THEN(X_CHOOSE_TAC `N:num`) THEN
    MATCH_MP_TAC INFINITE_SUPERSET THEN
    EXISTS_TAC `IMAGE (f:num->real^N) (from N)` THEN
    ASM_SIMP_TAC[SUBSET; FORALL_IN_IMAGE; IN_FROM; IN_INTER] THEN
    ASM_MESON_TAC[INFINITE_IMAGE_INJ; INFINITE_FROM]]);;


let INFINITE_OPEN_IN = 
prove
 (`!u s:real^N->bool.
      open_in (subtopology euclidean u) s /\ (?x. x IN s /\ x limit_point_of u)
      ==> INFINITE s`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_IN_OPEN]) THEN
  DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `t:real^N->bool` o
        GEN_REWRITE_RULE I [LIMPT_INFINITE_OPEN]) THEN
  FIRST_X_ASSUM SUBST_ALL_TAC THEN ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Condensation points.                                                      *)
(* ------------------------------------------------------------------------- *)

parse_as_infix ("condensation_point_of",(12,"right"));;


let condensation_point_of = new_definition
 `x condensation_point_of s <=>
        !t. x IN t /\ open t ==> ~COUNTABLE(s INTER t)`;;


let CONDENSATION_POINT_OF_SUBSET = 
prove
 (`!x:real^N s t.
        x condensation_point_of s /\ s SUBSET t ==> x condensation_point_of t`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  REWRITE_TAC[condensation_point_of] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN
  REWRITE_TAC[CONTRAPOS_THM] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] COUNTABLE_SUBSET) THEN
  ASM SET_TAC[]);;


let CONDENSATION_POINT_IMP_LIMPT = 
prove
 (`!x s. x condensation_point_of s ==> x limit_point_of s`,

  REWRITE_TAC[condensation_point_of; LIMPT_INFINITE_OPEN; INFINITE] THEN
  MESON_TAC[FINITE_IMP_COUNTABLE]);;

let CONDENSATION_POINT_INFINITE_BALL,CONDENSATION_POINT_INFINITE_CBALL =
  (CONJ_PAIR o prove)
 (`(!s x:real^N.
        x condensation_point_of s <=>
        !e. &0 < e ==> ~COUNTABLE(s INTER ball(x,e))) /\
   (!s x:real^N.
        x condensation_point_of s <=>
        !e. &0 < e ==> ~COUNTABLE(s INTER cball(x,e)))`,
  REWRITE_TAC[AND_FORALL_THM] THEN REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT
   `(p ==> q) /\ (q ==> r) /\ (r ==> p)
    ==> (p <=> q) /\ (p <=> r)`) THEN
  REWRITE_TAC[condensation_point_of] THEN REPEAT CONJ_TAC THENL
   [MESON_TAC[OPEN_BALL; CENTRE_IN_BALL];
    MESON_TAC[BALL_SUBSET_CBALL; COUNTABLE_SUBSET;
              SET_RULE `t SUBSET u ==> s INTER t SUBSET s INTER u`];
    MESON_TAC[COUNTABLE_SUBSET; OPEN_CONTAINS_CBALL;
              SET_RULE `t SUBSET u ==> s INTER t SUBSET s INTER u`]]);;

(* ------------------------------------------------------------------------- *)
(* Basic arithmetical combining theorems for limits.                         *)
(* ------------------------------------------------------------------------- *)


let LIM_LINEAR = 
prove
 (`!net:(A)net h f l.
        (f --> l) net /\ linear h ==> ((\x. h(f x)) --> h l) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM] THEN
  ASM_CASES_TAC `trivial_limit (net:(A)net)` THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN FIRST_ASSUM(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC o
    MATCH_MP LINEAR_BOUNDED_POS) THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / B`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; dist; GSYM LINEAR_SUB; REAL_LT_RDIV_EQ] THEN
  ASM_MESON_TAC[REAL_LET_TRANS; REAL_MUL_SYM]);;


let LIM_CONST = 
prove
 (`!net a:real^N. ((\x. a) --> a) net`,

  SIMP_TAC[LIM; DIST_REFL; trivial_limit] THEN MESON_TAC[]);;


let LIM_CMUL = 
prove
 (`!f l c. (f --> l) net ==> ((\x. c % f x) --> c % l) net`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_LINEAR THEN
  ASM_REWRITE_TAC[REWRITE_RULE[ETA_AX]
    (MATCH_MP LINEAR_COMPOSE_CMUL LINEAR_ID)]);;


let LIM_CMUL_EQ = 
prove
 (`!net f l c.
        ~(c = &0) ==> (((\x. c % f x) --> c % l) net <=> (f --> l) net)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN SIMP_TAC[LIM_CMUL] THEN
  DISCH_THEN(MP_TAC o SPEC `inv c:real` o MATCH_MP LIM_CMUL) THEN
  ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; VECTOR_MUL_LID; ETA_AX]);;


let LIM_NEG = 
prove
 (`!net f l:real^N. (f --> l) net ==> ((\x. --(f x)) --> --l) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM; dist] THEN
  REWRITE_TAC[VECTOR_ARITH `--x - --y = --(x - y:real^N)`; NORM_NEG]);;


let LIM_NEG_EQ = 
prove
 (`!net f l:real^N. ((\x. --(f x)) --> --l) net <=> (f --> l) net`,

  REPEAT GEN_TAC THEN EQ_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_NEG) THEN
  REWRITE_TAC[VECTOR_NEG_NEG; ETA_AX]);;


let LIM_ADD = 
prove
 (`!net:(A)net f g l m.
    (f --> l) net /\ (g --> m) net ==> ((\x. f(x) + g(x)) --> l + m) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM] THEN
  ASM_CASES_TAC `trivial_limit (net:(A)net)` THEN
  ASM_REWRITE_TAC[AND_FORALL_THM] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(MP_TAC o MATCH_MP NET_DILEMMA) THEN MATCH_MP_TAC MONO_EXISTS THEN
  MESON_TAC[REAL_HALF; DIST_TRIANGLE_ADD; REAL_LT_ADD2; REAL_LET_TRANS]);;


let LIM_ABS = 
prove
 (`!net:(A)net f:A->real^N l.
     (f --> l) net
     ==> ((\x. lambda i. (abs(f(x)$i))) --> (lambda i. abs(l$i)):real^N) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM] THEN
  ASM_CASES_TAC `trivial_limit (net:(A)net)` THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
  MATCH_MP_TAC MONO_AND THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC(NORM_ARITH
   `norm(x - y) <= norm(a - b) ==> dist(a,b) < e ==> dist(x,y) < e`) THEN
  MATCH_MP_TAC NORM_LE_COMPONENTWISE THEN
  SIMP_TAC[LAMBDA_BETA; VECTOR_SUB_COMPONENT] THEN
  REAL_ARITH_TAC);;


let LIM_SUB = 
prove
 (`!net:(A)net f g l m.
    (f --> l) net /\ (g --> m) net ==> ((\x. f(x) - g(x)) --> l - m) net`,

  REWRITE_TAC[real_sub; VECTOR_SUB] THEN ASM_SIMP_TAC[LIM_ADD; LIM_NEG]);;


let LIM_MAX = 
prove
 (`!net:(A)net f g l:real^N m:real^N.
    (f --> l) net /\ (g --> m) net
    ==> ((\x. lambda i. max (f(x)$i) (g(x)$i))
         --> (lambda i. max (l$i) (m$i)):real^N) net`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP LIM_ADD) THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP LIM_SUB) THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_ABS) THEN
  REWRITE_TAC[IMP_IMP] THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_ADD) THEN
  DISCH_THEN(MP_TAC o SPEC `inv(&2)` o MATCH_MP LIM_CMUL) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN BINOP_TAC THEN
  SIMP_TAC[FUN_EQ_THM; CART_EQ; VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT;
           VECTOR_SUB_COMPONENT; LAMBDA_BETA] THEN
  REAL_ARITH_TAC);;


let LIM_MIN = 
prove
 (`!net:(A)net f g l:real^N m:real^N.
    (f --> l) net /\ (g --> m) net
    ==> ((\x. lambda i. min (f(x)$i) (g(x)$i))
         --> (lambda i. min (l$i) (m$i)):real^N) net`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN(MP_TAC o MATCH_MP LIM_NEG)) THEN
  REWRITE_TAC[IMP_IMP] THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_NEG o MATCH_MP LIM_MAX) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN BINOP_TAC THEN
  SIMP_TAC[FUN_EQ_THM; CART_EQ; LAMBDA_BETA; VECTOR_NEG_COMPONENT] THEN
  REAL_ARITH_TAC);;


let LIM_NORM = 
prove
 (`!net f:A->real^N l.
        (f --> l) net ==> ((\x. lift(norm(f x))) --> lift(norm l)) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto; DIST_LIFT] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN
  REWRITE_TAC[] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  REWRITE_TAC[] THEN NORM_ARITH_TAC);;


let LIM_NULL = 
prove
 (`!net f l. (f --> l) net <=> ((\x. f(x) - l) --> vec 0) net`,

  REWRITE_TAC[LIM; dist; VECTOR_SUB_RZERO]);;


let LIM_NULL_NORM = 
prove
 (`!net f. (f --> vec 0) net <=> ((\x. lift(norm(f x))) --> vec 0) net`,

  REWRITE_TAC[LIM; dist; VECTOR_SUB_RZERO; REAL_ABS_NORM; NORM_LIFT]);;


let LIM_NULL_CMUL_EQ = 
prove
 (`!net f c.
        ~(c = &0) ==> (((\x. c % f x) --> vec 0) net <=> (f --> vec 0) net)`,


let LIM_NULL_CMUL = 
prove
 (`!net f c. (f --> vec 0) net ==> ((\x. c % f x) --> vec 0) net`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `c = &0` THEN
  ASM_SIMP_TAC[LIM_NULL_CMUL_EQ; VECTOR_MUL_LZERO; LIM_CONST]);;


let LIM_NULL_ADD = 
prove
 (`!net f g:A->real^N.
        (f --> vec 0) net /\ (g --> vec 0) net
        ==> ((\x. f x + g x) --> vec 0) net`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_ADD) THEN
  REWRITE_TAC[VECTOR_ADD_LID]);;


let LIM_NULL_SUB = 
prove
 (`!net f g:A->real^N.
        (f --> vec 0) net /\ (g --> vec 0) net
        ==> ((\x. f x - g x) --> vec 0) net`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_SUB) THEN
  REWRITE_TAC[VECTOR_SUB_RZERO]);;


let LIM_NULL_COMPARISON = 
prove
 (`!net f g. eventually (\x. norm(f x) <= g x) net /\
             ((\x. lift(g x)) --> vec 0) net
             ==> (f --> vec 0) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto; RIGHT_AND_FORALL_THM] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  REWRITE_TAC[dist; VECTOR_SUB_RZERO; NORM_LIFT] THEN REAL_ARITH_TAC);;


let LIM_COMPONENT = 
prove
 (`!net f i l:real^N. (f --> l) net /\ 1 <= i /\ i <= dimindex(:N)
                      ==> ((\a. lift(f(a)$i)) --> lift(l$i)) net`,

  REWRITE_TAC[LIM; dist; GSYM LIFT_SUB; NORM_LIFT] THEN
  SIMP_TAC[GSYM VECTOR_SUB_COMPONENT] THEN
  MESON_TAC[COMPONENT_LE_NORM; REAL_LET_TRANS]);;


let LIM_TRANSFORM_BOUND = 
prove
 (`!f g. eventually (\n. norm(f n) <= norm(g n)) net /\ (g --> vec 0) net
         ==> (f --> vec 0) net`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[tendsto; RIGHT_AND_FORALL_THM] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  REWRITE_TAC[dist; VECTOR_SUB_RZERO] THEN REAL_ARITH_TAC);;


let LIM_NULL_CMUL_BOUNDED = 
prove
 (`!f g:A->real^N B.
        eventually (\a. g a = vec 0 \/ abs(f a) <= B) net /\
        (g --> vec 0) net
        ==> ((\n. f n % g n) --> vec 0) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto] THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / (abs B + &1)`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_ARITH `&0 < abs x + &1`] THEN
  UNDISCH_TAC `eventually (\a. g a:real^N = vec 0 \/ abs(f a) <= B)
                           (net:(A net))` THEN
  REWRITE_TAC[IMP_IMP; GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MP) THEN
  REWRITE_TAC[dist; VECTOR_SUB_RZERO; o_THM; NORM_LIFT; NORM_MUL] THEN
  MATCH_MP_TAC ALWAYS_EVENTUALLY THEN X_GEN_TAC `x:A` THEN REWRITE_TAC[] THEN
  ASM_CASES_TAC `(g:A->real^N) x = vec 0` THEN
  ASM_REWRITE_TAC[NORM_0; REAL_MUL_RZERO] THEN
  STRIP_TAC THEN MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `B * e / (abs B + &1)` THEN
  ASM_SIMP_TAC[REAL_LE_MUL2; REAL_ABS_POS; NORM_POS_LE; REAL_LT_IMP_LE] THEN
  REWRITE_TAC[REAL_ARITH `c * (a / b) = (c * a) / b`] THEN
  SIMP_TAC[REAL_LT_LDIV_EQ; REAL_ARITH `&0 < abs x + &1`] THEN
  MATCH_MP_TAC(REAL_ARITH
   `e * B <= e * abs B /\ &0 < e ==> B * e < e * (abs B + &1)`) THEN
  ASM_SIMP_TAC[REAL_LE_LMUL_EQ] THEN REAL_ARITH_TAC);;


let LIM_NULL_VMUL_BOUNDED = 
prove
 (`!f g:A->real^N B.
        ((lift o f) --> vec 0) net /\
        eventually (\a. f a = &0 \/ norm(g a) <= B) net
        ==> ((\n. f n % g n) --> vec 0) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto] THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / (abs B + &1)`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_ARITH `&0 < abs x + &1`] THEN
  UNDISCH_TAC `eventually(\a. f a = &0 \/ norm((g:A->real^N) a) <= B) net` THEN
  REWRITE_TAC[IMP_IMP; GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MP) THEN
  REWRITE_TAC[dist; VECTOR_SUB_RZERO; o_THM; NORM_LIFT; NORM_MUL] THEN
  MATCH_MP_TAC ALWAYS_EVENTUALLY THEN X_GEN_TAC `x:A` THEN REWRITE_TAC[] THEN
  ASM_CASES_TAC `(f:A->real) x = &0` THEN
  ASM_REWRITE_TAC[REAL_ABS_NUM; REAL_MUL_LZERO] THEN
  STRIP_TAC THEN MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `e / (abs B + &1) * B` THEN
  ASM_SIMP_TAC[REAL_LE_MUL2; REAL_ABS_POS; NORM_POS_LE; REAL_LT_IMP_LE] THEN
  REWRITE_TAC[REAL_ARITH `(a / b) * c = (a * c) / b`] THEN
  SIMP_TAC[REAL_LT_LDIV_EQ; REAL_ARITH `&0 < abs x + &1`] THEN
  MATCH_MP_TAC(REAL_ARITH
   `e * B <= e * abs B /\ &0 < e ==> e * B < e * (abs B + &1)`) THEN
  ASM_SIMP_TAC[REAL_LE_LMUL_EQ] THEN REAL_ARITH_TAC);;


let LIM_VSUM = 
prove
 (`!net f:A->B->real^N l s.
        FINITE s /\ (!i. i IN s ==> ((f i) --> (l i)) net)
        ==> ((\x. vsum s (\i. f i x)) --> vsum s l) net`,

  REPLICATE_TAC 3 GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  SIMP_TAC[VSUM_CLAUSES; LIM_CONST; LIM_ADD; IN_INSERT; ETA_AX]);;

(* ------------------------------------------------------------------------- *)
(* Deducing things about the limit from the elements.                        *)
(* ------------------------------------------------------------------------- *)


let LIM_IN_CLOSED_SET = 
prove
 (`!net f:A->real^N s l.
        closed s /\ eventually (\x. f(x) IN s) net /\
        ~(trivial_limit net) /\ (f --> l) net
        ==> l IN s`,

  REWRITE_TAC[closed] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC(SET_RULE `~(x IN (UNIV DIFF s)) ==> x IN s`) THEN
  DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `l:real^N` o GEN_REWRITE_RULE I
          [OPEN_CONTAINS_BALL]) THEN
  ASM_REWRITE_TAC[SUBSET; IN_BALL; IN_DIFF; IN_UNION] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e:real` o GEN_REWRITE_RULE I [tendsto]) THEN
  UNDISCH_TAC `eventually (\x. (f:A->real^N) x IN s) net` THEN
  ASM_REWRITE_TAC[GSYM EVENTUALLY_AND; TAUT `a ==> ~b <=> ~(a /\ b)`] THEN
  MATCH_MP_TAC NOT_EVENTUALLY THEN ASM_MESON_TAC[DIST_SYM]);;

(* ------------------------------------------------------------------------- *)
(* Need to prove closed(cball(x,e)) before deducing this as a corollary.     *)
(* ------------------------------------------------------------------------- *)


let LIM_NORM_UBOUND = 
prove
 (`!net:(A)net f (l:real^N) b.
      ~(trivial_limit net) /\
      (f --> l) net /\
      eventually (\x. norm(f x) <= b) net
      ==> norm(l) <= b`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_REWRITE_TAC[LIM] THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_REWRITE_TAC[eventually] THEN
  STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `?x:A. dist(f(x):real^N,l) < norm(l:real^N) - b /\ norm(f x) <= b`
  (CHOOSE_THEN MP_TAC) THENL [ASM_MESON_TAC[NET]; ALL_TAC] THEN
  REWRITE_TAC[REAL_NOT_LT; REAL_LE_SUB_RADD; DE_MORGAN_THM; dist] THEN
  NORM_ARITH_TAC);;


let LIM_NORM_LBOUND = 
prove
 (`!net:(A)net f (l:real^N) b.
      ~(trivial_limit net) /\ (f --> l) net /\
      eventually (\x. b <= norm(f x)) net
      ==> b <= norm(l)`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_REWRITE_TAC[LIM] THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_REWRITE_TAC[eventually] THEN
  STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `?x:A. dist(f(x):real^N,l) < b - norm(l:real^N) /\ b <= norm(f x)`
  (CHOOSE_THEN MP_TAC) THENL [ASM_MESON_TAC[NET]; ALL_TAC] THEN
  REWRITE_TAC[REAL_NOT_LT; REAL_LE_SUB_RADD; DE_MORGAN_THM; dist] THEN
  NORM_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Uniqueness of the limit, when nontrivial.                                 *)
(* ------------------------------------------------------------------------- *)


let LIM_UNIQUE = 
prove
 (`!net:(A)net f l:real^N l'.
      ~(trivial_limit net) /\ (f --> l) net /\ (f --> l') net ==> (l = l')`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(ASSUME_TAC o REWRITE_RULE[VECTOR_SUB_REFL] o MATCH_MP LIM_SUB) THEN
  SUBGOAL_THEN `!e. &0 < e ==> norm(l:real^N - l') <= e` MP_TAC THENL
   [GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC LIM_NORM_UBOUND THEN
    MAP_EVERY EXISTS_TAC [`net:(A)net`; `\x:A. vec 0 : real^N`] THEN
    ASM_SIMP_TAC[NORM_0; REAL_LT_IMP_LE; eventually] THEN
    ASM_MESON_TAC[trivial_limit];
    ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN REWRITE_TAC[DIST_NZ; dist] THEN
    DISCH_TAC THEN DISCH_THEN(MP_TAC o SPEC `norm(l - l':real^N) / &2`) THEN
    ASM_SIMP_TAC[REAL_LT_RDIV_EQ; REAL_LE_RDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
    UNDISCH_TAC `&0 < norm(l - l':real^N)` THEN REAL_ARITH_TAC]);;


let TENDSTO_LIM = 
prove
 (`!net f l. ~(trivial_limit net) /\ (f --> l) net ==> lim net f = l`,

  REWRITE_TAC[lim] THEN MESON_TAC[LIM_UNIQUE]);;


let LIM_CONST_EQ = 
prove
 (`!net:(A net) c d:real^N.
        ((\x. c) --> d) net <=> trivial_limit net \/ c = d`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `trivial_limit (net:A net)` THEN ASM_REWRITE_TAC[] THENL
   [ASM_REWRITE_TAC[LIM]; ALL_TAC] THEN
  EQ_TAC THEN SIMP_TAC[LIM_CONST] THEN DISCH_TAC THEN
  MATCH_MP_TAC(SPEC `net:A net` LIM_UNIQUE) THEN
  EXISTS_TAC `(\x. c):A->real^N` THEN ASM_REWRITE_TAC[LIM_CONST]);;

(* ------------------------------------------------------------------------- *)
(* Some unwieldy but occasionally useful theorems about uniform limits.      *)
(* ------------------------------------------------------------------------- *)


let UNIFORM_LIM_ADD = 
prove
 (`!net:(A)net P f g l m.
        (!e. &0 < e
             ==> eventually (\x. !n:B. P n ==> norm(f n x - l n) < e) net) /\
        (!e. &0 < e
             ==> eventually (\x. !n. P n ==> norm(g n x - m n) < e) net)
        ==> !e. &0 < e
                ==> eventually
                     (\x. !n. P n
                              ==> norm((f n x + g n x) - (l n + m n)) < e)
                     net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[AND_FORALL_THM] THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF; GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  GEN_TAC THEN REWRITE_TAC[AND_FORALL_THM] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `n:B` THEN
  ASM_CASES_TAC `(P:B->bool) n` THEN ASM_REWRITE_TAC[] THEN
  CONV_TAC NORM_ARITH);;


let UNIFORM_LIM_SUB = 
prove
 (`!net:(A)net P f g l m.
        (!e. &0 < e
             ==> eventually (\x. !n:B. P n ==> norm(f n x - l n) < e) net) /\
        (!e. &0 < e
             ==> eventually (\x. !n. P n ==> norm(g n x - m n) < e) net)
        ==> !e. &0 < e
                ==> eventually
                     (\x. !n. P n
                              ==> norm((f n x - g n x) - (l n - m n)) < e)
                     net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[AND_FORALL_THM] THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF; GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  GEN_TAC THEN REWRITE_TAC[AND_FORALL_THM] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `n:B` THEN
  ASM_CASES_TAC `(P:B->bool) n` THEN ASM_REWRITE_TAC[] THEN
  CONV_TAC NORM_ARITH);;

(* ------------------------------------------------------------------------- *)
(* Limit under bilinear function, uniform version first.                     *)
(* ------------------------------------------------------------------------- *)


let UNIFORM_LIM_BILINEAR = 
prove
 (`!net:(A)net P (h:real^M->real^N->real^P) f g l m b1 b2.
        bilinear h /\
        eventually (\x. !n. P n ==> norm(l n) <= b1) net /\
        eventually (\x. !n. P n ==> norm(m n) <= b2) net /\
        (!e. &0 < e
             ==> eventually (\x. !n:B. P n ==> norm(f n x - l n) < e) net) /\
        (!e. &0 < e
             ==> eventually (\x. !n. P n ==> norm(g n x - m n) < e) net)
        ==> !e. &0 < e
                ==> eventually
                     (\x. !n. P n
                              ==> norm(h (f n x) (g n x) - h (l n) (m n)) < e)
                     net`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  FIRST_ASSUM(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC o  MATCH_MP
   BILINEAR_BOUNDED_POS) THEN
  REWRITE_TAC[AND_FORALL_THM; RIGHT_AND_FORALL_THM] THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC
   `min (abs b2 + &1) (e / &2 / (B * (abs b1 + abs b2 + &2)))`) THEN
  ASM_SIMP_TAC[REAL_HALF; REAL_LT_DIV; REAL_LT_MUL; REAL_LT_MIN;
               REAL_ARITH `&0 < abs x + &1`;
               REAL_ARITH `&0 < abs x + abs y + &2`] THEN
  REWRITE_TAC[GSYM EVENTUALLY_AND] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  X_GEN_TAC `x:A` THEN REWRITE_TAC[AND_FORALL_THM] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `n:B` THEN
  ASM_CASES_TAC `(P:B->bool) n` THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH
    `h a b - h c d :real^N = (h a b - h a d) + (h a d - h c d)`] THEN
  ASM_SIMP_TAC[GSYM BILINEAR_LSUB; GSYM BILINEAR_RSUB] THEN
  MATCH_MP_TAC NORM_TRIANGLE_LT THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP
   (MESON[REAL_LE_ADD2; REAL_LET_TRANS]
     `(!x y. norm(h x y:real^P) <= B * norm x * norm y)
       ==> B * norm a * norm b + B * norm c * norm d < e
           ==> norm(h a b) + norm(h c d) < e`)) THEN
  MATCH_MP_TAC(REAL_ARITH
   `x * B < e / &2 /\ y * B < e / &2 ==> B * x + B * y < e`) THEN
  CONJ_TAC THEN ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ] THENL
   [ONCE_REWRITE_TAC[REAL_MUL_SYM]; ALL_TAC] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `e / &2 / (B * (abs b1 + abs b2 + &2)) *
             (abs b1 + abs b2 + &1)` THEN
  (CONJ_TAC THENL
    [MATCH_MP_TAC REAL_LE_MUL2 THEN
     ASM_SIMP_TAC[NORM_POS_LE; REAL_LT_IMP_LE] THEN
     ASM_SIMP_TAC[REAL_ARITH `a <= b2 ==> a <= abs b1 + abs b2 + &1`] THEN
     ASM_MESON_TAC[NORM_ARITH
       `norm(f - l:real^P) < abs b2 + &1 /\ norm(l) <= b1
        ==> norm(f) <= abs b1 + abs b2 + &1`];
     ONCE_REWRITE_TAC[real_div] THEN
     ASM_SIMP_TAC[REAL_LT_LMUL_EQ; REAL_HALF; GSYM REAL_MUL_ASSOC;
                  REAL_INV_MUL] THEN
     REWRITE_TAC[REAL_ARITH `B * inv x * y < B <=> B * y / x < B * &1`] THEN
     ASM_SIMP_TAC[REAL_LT_INV_EQ; REAL_LT_LMUL_EQ; REAL_LT_LDIV_EQ;
                  REAL_ARITH `&0 < abs x + abs y + &2`] THEN
     REAL_ARITH_TAC]));;


let LIM_BILINEAR = 
prove
 (`!net:(A)net (h:real^M->real^N->real^P) f g l m.
        (f --> l) net /\ (g --> m) net /\ bilinear h
        ==> ((\x. h (f x) (g x)) --> (h l m)) net`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL
   [`net:(A)net`; `\x:one. T`; `h:real^M->real^N->real^P`;
    `\n:one. (f:A->real^M)`; `\n:one. (g:A->real^N)`;
    `\n:one. (l:real^M)`; `\n:one. (m:real^N)`;
    `norm(l:real^M)`; `norm(m:real^N)`]
   UNIFORM_LIM_BILINEAR) THEN
  ASM_REWRITE_TAC[REAL_LE_REFL; EVENTUALLY_TRUE] THEN
  ASM_REWRITE_TAC[GSYM dist; GSYM tendsto]);;

(* ------------------------------------------------------------------------- *)
(* These are special for limits out of the same vector space.                *)
(* ------------------------------------------------------------------------- *)


let LIM_WITHIN_ID = 
prove
 (`!a s. ((\x. x) --> a) (at a within s)`,

  REWRITE_TAC[LIM_WITHIN] THEN MESON_TAC[]);;


let LIM_AT_ID = 
prove
 (`!a. ((\x. x) --> a) (at a)`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN REWRITE_TAC[LIM_WITHIN_ID]);;


let LIM_AT_ZERO = 
prove
 (`!f:real^M->real^N l a.
        (f --> l) (at a) <=> ((\x. f(a + x)) --> l) (at(vec 0))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM_AT] THEN
  AP_TERM_TAC THEN ABS_TAC THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  AP_TERM_TAC THEN ABS_TAC THEN
  ASM_CASES_TAC `&0 < d` THEN ASM_REWRITE_TAC[] THEN
  EQ_TAC THEN DISCH_TAC THEN X_GEN_TAC `x:real^M` THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `a + x:real^M`) THEN
    REWRITE_TAC[dist; VECTOR_ADD_SUB; VECTOR_SUB_RZERO];
    FIRST_X_ASSUM(MP_TAC o SPEC `x - a:real^M`) THEN
    REWRITE_TAC[dist; VECTOR_SUB_RZERO; VECTOR_SUB_ADD2]]);;

(* ------------------------------------------------------------------------- *)
(* It's also sometimes useful to extract the limit point from the net.       *)
(* ------------------------------------------------------------------------- *)


let netlimit = new_definition
  `netlimit net = @a. !x. ~(netord net x a)`;;


let NETLIMIT_WITHIN = 
prove
 (`!a:real^N s. ~(trivial_limit (at a within s))
                ==> (netlimit (at a within s) = a)`,

  REWRITE_TAC[trivial_limit; netlimit; AT; WITHIN; DE_MORGAN_THM] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC SELECT_UNIQUE THEN REWRITE_TAC[] THEN
  SUBGOAL_THEN
   `!x:real^N. ~(&0 < dist(x,a) /\ dist(x,a) <= dist(a,a) /\ x IN s)`
  ASSUME_TAC THENL
   [ASM_MESON_TAC[DIST_REFL; REAL_NOT_LT]; ASM_MESON_TAC[]]);;


let NETLIMIT_AT = 
prove
 (`!a. netlimit(at a) = a`,

  GEN_TAC THEN ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  MATCH_MP_TAC NETLIMIT_WITHIN THEN
  SIMP_TAC[TRIVIAL_LIMIT_AT; WITHIN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Transformation of limit.                                                  *)
(* ------------------------------------------------------------------------- *)


let LIM_TRANSFORM = 
prove
 (`!net f g l.
     ((\x. f x - g x) --> vec 0) net /\ (f --> l) net ==> (g --> l) net`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP LIM_SUB) THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_NEG) THEN MATCH_MP_TAC EQ_IMP THEN
  AP_THM_TAC THEN BINOP_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN
  VECTOR_ARITH_TAC);;


let LIM_TRANSFORM_EVENTUALLY = 
prove
 (`!net f g l.
        eventually (\x. f x = g x) net /\ (f --> l) net ==> (g --> l) net`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[GSYM VECTOR_SUB_EQ] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (MP_TAC o MATCH_MP LIM_EVENTUALLY) MP_TAC) THEN
  MESON_TAC[LIM_TRANSFORM]);;


let LIM_TRANSFORM_WITHIN = 
prove
 (`!f g x s d.
        &0 < d /\
        (!x'. x' IN s /\ &0 < dist(x',x) /\ dist(x',x) < d ==> f(x') = g(x')) /\
        (f --> l) (at x within s)
        ==> (g --> l) (at x within s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  DISCH_TAC THEN DISCH_TAC THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] LIM_TRANSFORM) THEN
  REWRITE_TAC[LIM_WITHIN] THEN REPEAT STRIP_TAC THEN EXISTS_TAC `d:real` THEN
  ASM_SIMP_TAC[VECTOR_SUB_REFL; DIST_REFL]);;


let LIM_TRANSFORM_AT = 
prove
 (`!f g x d.
        &0 < d /\
        (!x'. &0 < dist(x',x) /\ dist(x',x) < d ==> f(x') = g(x')) /\
        (f --> l) (at x)
        ==> (g --> l) (at x)`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN MESON_TAC[LIM_TRANSFORM_WITHIN]);;


let LIM_TRANSFORM_EQ = 
prove
 (`!net f:A->real^N g l.
     ((\x. f x - g x) --> vec 0) net ==> ((f --> l) net <=> (g --> l) net)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN
  DISCH_TAC THEN MATCH_MP_TAC LIM_TRANSFORM THENL
   [EXISTS_TAC `f:A->real^N` THEN ASM_REWRITE_TAC[];
    EXISTS_TAC `g:A->real^N` THEN ASM_REWRITE_TAC[] THEN
    ONCE_REWRITE_TAC[GSYM LIM_NEG_EQ] THEN
    ASM_REWRITE_TAC[VECTOR_NEG_SUB; VECTOR_NEG_0]]);;


let LIM_TRANSFORM_WITHIN_SET = 
prove
 (`!f a s t.
        eventually (\x. x IN s <=> x IN t) (at a)
        ==> ((f --> l) (at a within s) <=> (f --> l) (at a within t))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[EVENTUALLY_AT; LIM_WITHIN] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  EQ_TAC THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e:real`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `min d k:real` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Common case assuming being away from some crucial point like 0.           *)
(* ------------------------------------------------------------------------- *)


let LIM_TRANSFORM_AWAY_WITHIN = 
prove
 (`!f:real^M->real^N g a b s.
        ~(a = b) /\
        (!x. x IN s /\ ~(x = a) /\ ~(x = b) ==> f(x) = g(x)) /\
        (f --> l) (at a within s)
        ==> (g --> l) (at a within s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_TRANSFORM_WITHIN THEN
  MAP_EVERY EXISTS_TAC [`f:real^M->real^N`; `dist(a:real^M,b)`] THEN
  ASM_REWRITE_TAC[GSYM DIST_NZ] THEN X_GEN_TAC `y:real^M` THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_MESON_TAC[DIST_SYM; REAL_LT_REFL]);;


let LIM_TRANSFORM_AWAY_AT = 
prove
 (`!f:real^M->real^N g a b.
        ~(a = b) /\
        (!x. ~(x = a) /\ ~(x = b) ==> f(x) = g(x)) /\
        (f --> l) (at a)
        ==> (g --> l) (at a)`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  MESON_TAC[LIM_TRANSFORM_AWAY_WITHIN]);;

(* ------------------------------------------------------------------------- *)
(* Alternatively, within an open set.                                        *)
(* ------------------------------------------------------------------------- *)


let LIM_TRANSFORM_WITHIN_OPEN = 
prove
 (`!f g:real^M->real^N s a l.
        open s /\ a IN s /\
        (!x. x IN s /\ ~(x = a) ==> f x = g x) /\
        (f --> l) (at a)
        ==> (g --> l) (at a)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_TRANSFORM_AT THEN
  EXISTS_TAC `f:real^M->real^N` THEN ASM_REWRITE_TAC[] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_CONTAINS_BALL]) THEN
  DISCH_THEN(MP_TAC o SPEC `a:real^M`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[SUBSET; IN_BALL] THEN
  ASM_MESON_TAC[DIST_NZ; DIST_SYM]);;


let LIM_TRANSFORM_WITHIN_OPEN_IN = 
prove
 (`!f g:real^M->real^N s t a l.
        open_in (subtopology euclidean t) s /\ a IN s /\
        (!x. x IN s /\ ~(x = a) ==> f x = g x) /\
        (f --> l) (at a within t)
        ==> (g --> l) (at a within t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_TRANSFORM_WITHIN THEN
  EXISTS_TAC `f:real^M->real^N` THEN ASM_REWRITE_TAC[] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_IN_CONTAINS_BALL]) THEN
  DISCH_THEN(MP_TAC o SPEC `a:real^M` o CONJUNCT2) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[SUBSET; IN_INTER; IN_BALL] THEN
  ASM_MESON_TAC[DIST_NZ; DIST_SYM]);;

(* ------------------------------------------------------------------------- *)
(* Another quite common idiom of an explicit conditional in a sequence.      *)
(* ------------------------------------------------------------------------- *)


let LIM_CASES_FINITE_SEQUENTIALLY = 
prove
 (`!f g l. FINITE {n | P n}
           ==> (((\n. if P n then f n else g n) --> l) sequentially <=>
                (g --> l) sequentially)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] LIM_TRANSFORM_EVENTUALLY) THEN
  FIRST_ASSUM(MP_TAC o SPEC `\n:num. n` o MATCH_MP UPPER_BOUND_FINITE_SET) THEN
  REWRITE_TAC[IN_ELIM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `N:num` THEN DISCH_TAC THEN SIMP_TAC[EVENTUALLY_SEQUENTIALLY] THEN
  EXISTS_TAC `N + 1` THEN
  ASM_MESON_TAC[ARITH_RULE `~(x <= n /\ n + 1 <= x)`]);;


let LIM_CASES_COFINITE_SEQUENTIALLY = 
prove
 (`!f g l. FINITE {n | ~P n}
           ==> (((\n. if P n then f n else g n) --> l) sequentially <=>
                (f --> l) sequentially)`,

  ONCE_REWRITE_TAC[TAUT `(if p then x else y) = (if ~p then y else x)`] THEN
  REWRITE_TAC[LIM_CASES_FINITE_SEQUENTIALLY]);;


let LIM_CASES_SEQUENTIALLY = 
prove
 (`!f g l m. (((\n. if m <= n then f n else g n) --> l) sequentially <=>
              (f --> l) sequentially) /\
             (((\n. if m < n then f n else g n) --> l) sequentially <=>
              (f --> l) sequentially) /\
             (((\n. if n <= m then f n else g n) --> l) sequentially <=>
              (g --> l) sequentially) /\
             (((\n. if n < m then f n else g n) --> l) sequentially <=>
              (g --> l) sequentially)`,

(* ------------------------------------------------------------------------- *)
(* A congruence rule allowing us to transform limits assuming not at point.  *)
(* ------------------------------------------------------------------------- *)


let LIM_CONG_WITHIN = 
prove
 (`(!x. ~(x = a) ==> f x = g x)
   ==> (((\x. f x) --> l) (at a within s) <=> ((g --> l) (at a within s)))`,

  REWRITE_TAC[LIM_WITHIN; GSYM DIST_NZ] THEN SIMP_TAC[]);;


let LIM_CONG_AT = 
prove
 (`(!x. ~(x = a) ==> f x = g x)
   ==> (((\x. f x) --> l) (at a) <=> ((g --> l) (at a)))`,

  REWRITE_TAC[LIM_AT; GSYM DIST_NZ] THEN SIMP_TAC[]);;

extend_basic_congs [LIM_CONG_WITHIN; LIM_CONG_AT];;

(* ------------------------------------------------------------------------- *)
(* Useful lemmas on closure and set of possible sequential limits.           *)
(* ------------------------------------------------------------------------- *)


let CLOSURE_SEQUENTIAL = 
prove
 (`!s l:real^N.
     l IN closure(s) <=> ?x. (!n. x(n) IN s) /\ (x --> l) sequentially`,

  REWRITE_TAC[closure; IN_UNION; LIMPT_SEQUENTIAL; IN_ELIM_THM; IN_DELETE] THEN
  REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT
    `((b ==> c) /\ (~a /\ c ==> b)) /\ (a ==> c) ==> (a \/ b <=> c)`) THEN
  CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN DISCH_TAC THEN
  EXISTS_TAC `\n:num. l:real^N` THEN
  ASM_REWRITE_TAC[LIM_CONST]);;


let CLOSED_CONTAINS_SEQUENTIAL_LIMIT = 
prove
 (`!s x l:real^N.
        closed s /\ (!n. x n IN s) /\ (x --> l) sequentially ==> l IN s`,


let CLOSED_SEQUENTIAL_LIMITS = 
prove
 (`!s. closed s <=>
       !x l. (!n. x(n) IN s) /\ (x --> l) sequentially ==> l IN s`,


let CLOSURE_APPROACHABLE = 
prove
 (`!x s. x IN closure(s) <=> !e. &0 < e ==> ?y. y IN s /\ dist(y,x) < e`,

  REWRITE_TAC[closure; LIMPT_APPROACHABLE; IN_UNION; IN_ELIM_THM] THEN
  MESON_TAC[DIST_REFL]);;


let CLOSED_APPROACHABLE = 
prove
 (`!x s. closed s
         ==> ((!e. &0 < e ==> ?y. y IN s /\ dist(y,x) < e) <=> x IN s)`,


let IN_CLOSURE_DELETE = 
prove
 (`!s x:real^N. x IN closure(s DELETE x) <=> x limit_point_of s`,

(* ------------------------------------------------------------------------- *)
(* Some other lemmas about sequences.                                        *)
(* ------------------------------------------------------------------------- *)


let SEQ_OFFSET = 
prove
 (`!f l k. (f --> l) sequentially ==> ((\i. f(i + k)) --> l) sequentially`,

  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  MESON_TAC[ARITH_RULE `N <= n ==> N <= n + k:num`]);;


let SEQ_OFFSET_NEG = 
prove
 (`!f l k. (f --> l) sequentially ==> ((\i. f(i - k)) --> l) sequentially`,

  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  MESON_TAC[ARITH_RULE `N + k <= n ==> N <= n - k:num`]);;


let SEQ_OFFSET_REV = 
prove
 (`!f l k. ((\i. f(i + k)) --> l) sequentially ==> (f --> l) sequentially`,

  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  MESON_TAC[ARITH_RULE `N + k <= n ==> N <= n - k /\ (n - k) + k = n:num`]);;


let SEQ_HARMONIC = 
prove
 (`((\n. lift(inv(&n))) --> vec 0) sequentially`,

  REWRITE_TAC[LIM_SEQUENTIALLY] THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_ASSUM(X_CHOOSE_THEN `N:num` STRIP_ASSUME_TAC o
    GEN_REWRITE_RULE I [REAL_ARCH_INV]) THEN
  EXISTS_TAC `N:num` THEN REPEAT STRIP_TAC THEN
  REWRITE_TAC[dist; VECTOR_SUB_RZERO; NORM_LIFT] THEN
  ASM_REWRITE_TAC[REAL_ABS_INV; REAL_ABS_NUM] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `inv(&N)` THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_INV2 THEN
  ASM_REWRITE_TAC[REAL_OF_NUM_LT; REAL_OF_NUM_LE; LT_NZ]);;

(* ------------------------------------------------------------------------- *)
(* More properties of closed balls.                                          *)
(* ------------------------------------------------------------------------- *)


let CLOSED_CBALL = 
prove
 (`!x:real^N e. closed(cball(x,e))`,

  REWRITE_TAC[CLOSED_SEQUENTIAL_LIMITS; IN_CBALL; dist] THEN
  GEN_TAC THEN GEN_TAC THEN X_GEN_TAC `s:num->real^N` THEN
  X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_NORM_UBOUND) THEN
  EXISTS_TAC `\n. x - (s:num->real^N) n` THEN
  REWRITE_TAC[TRIVIAL_LIMIT_SEQUENTIALLY; EVENTUALLY_SEQUENTIALLY] THEN
  ASM_SIMP_TAC[LIM_SUB; LIM_CONST; SEQUENTIALLY] THEN MESON_TAC[GE_REFL]);;


let IN_INTERIOR_CBALL = 
prove
 (`!x s. x IN interior s <=> ?e. &0 < e /\ cball(x,e) SUBSET s`,


let LIMPT_BALL = 
prove
 (`!x:real^N y e. y limit_point_of ball(x,e) <=> &0 < e /\ y IN cball(x,e)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `&0 < e` THENL
   [ALL_TAC; ASM_MESON_TAC[LIMPT_EMPTY; REAL_NOT_LT; BALL_EQ_EMPTY]] THEN
  ASM_REWRITE_TAC[] THEN EQ_TAC THENL
   [MESON_TAC[CLOSED_CBALL; CLOSED_LIMPT; LIMPT_SUBSET; BALL_SUBSET_CBALL];
    REWRITE_TAC[IN_CBALL; LIMPT_APPROACHABLE; IN_BALL]] THEN
  DISCH_TAC THEN X_GEN_TAC `d:real` THEN DISCH_TAC THEN
  ASM_CASES_TAC `y:real^N = x` THEN ASM_REWRITE_TAC[DIST_NZ] THENL
   [MP_TAC(SPECL [`d:real`; `e:real`] REAL_DOWN2) THEN
    ASM_REWRITE_TAC[] THEN
    GEN_MESON_TAC 0 40 1 [VECTOR_CHOOSE_DIST; DIST_SYM; REAL_LT_IMP_LE];
    ALL_TAC] THEN
  MP_TAC(SPECL [`norm(y:real^N - x)`; `d:real`] REAL_DOWN2) THEN
  RULE_ASSUM_TAC(REWRITE_RULE[DIST_NZ; dist]) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `(y:real^N) - (k / dist(y,x)) % (y - x)` THEN
  REWRITE_TAC[dist; VECTOR_ARITH `(y - c % z) - y = --c % z`] THEN
  REWRITE_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM; REAL_ABS_NEG] THEN
  ASM_SIMP_TAC[REAL_DIV_RMUL; REAL_LT_IMP_NZ] THEN
  REWRITE_TAC[VECTOR_ARITH `x - (y - k % (y - x)) = (&1 - k) % (x - y)`] THEN
  ASM_SIMP_TAC[REAL_ARITH `&0 < k ==> &0 < abs k`; NORM_MUL] THEN
  ASM_SIMP_TAC[REAL_ARITH `&0 < k /\ k < d ==> abs k < d`] THEN
  MATCH_MP_TAC REAL_LTE_TRANS THEN EXISTS_TAC `norm(x:real^N - y)` THEN
  ASM_REWRITE_TAC[] THEN GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_LID] THEN
  MATCH_MP_TAC REAL_LT_RMUL THEN CONJ_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[NORM_SUB]] THEN
  MATCH_MP_TAC(REAL_ARITH `&0 < k /\ k < &1 ==> abs(&1 - k) < &1`) THEN
  ASM_SIMP_TAC[REAL_LT_LDIV_EQ; REAL_LT_RDIV_EQ; REAL_MUL_LZERO;
               REAL_MUL_LID]);;


let CLOSURE_BALL = 
prove
 (`!x:real^N e. &0 < e ==> (closure(ball(x,e)) = cball(x,e))`,

  SIMP_TAC[EXTENSION; closure; IN_ELIM_THM; IN_UNION; LIMPT_BALL] THEN
  REWRITE_TAC[IN_BALL; IN_CBALL] THEN REAL_ARITH_TAC);;


let INTERIOR_BALL = 
prove
 (`!a r. interior(ball(a,r)) = ball(a,r)`,

  SIMP_TAC[INTERIOR_OPEN; OPEN_BALL]);;


let INTERIOR_CBALL = 
prove
 (`!x:real^N e. interior(cball(x,e)) = ball(x,e)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `&0 <= e` THENL
   [ALL_TAC;
    SUBGOAL_THEN `cball(x:real^N,e) = {} /\ ball(x:real^N,e) = {}`
     (fun th -> REWRITE_TAC[th; INTERIOR_EMPTY]) THEN
    REWRITE_TAC[IN_BALL; IN_CBALL; EXTENSION; NOT_IN_EMPTY] THEN
    CONJ_TAC THEN X_GEN_TAC `y:real^N` THEN
    MP_TAC(ISPECL [`x:real^N`; `y:real^N`] DIST_POS_LE) THEN
    POP_ASSUM MP_TAC THEN REAL_ARITH_TAC] THEN
  MATCH_MP_TAC INTERIOR_UNIQUE THEN
  REWRITE_TAC[BALL_SUBSET_CBALL; OPEN_BALL] THEN
  X_GEN_TAC `t:real^N->bool` THEN
  SIMP_TAC[SUBSET; IN_CBALL; IN_BALL; REAL_LT_LE] THEN STRIP_TAC THEN
  X_GEN_TAC `z:real^N` THEN DISCH_TAC THEN DISCH_THEN(SUBST_ALL_TAC o SYM) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `z:real^N` o GEN_REWRITE_RULE I [open_def]) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(X_CHOOSE_THEN `d:real` MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_CASES_TAC `z:real^N = x` THENL
   [FIRST_X_ASSUM SUBST_ALL_TAC THEN
    FIRST_X_ASSUM(X_CHOOSE_TAC `k:real` o MATCH_MP REAL_DOWN) THEN
    SUBGOAL_THEN `?w:real^N. dist(w,x) = k` STRIP_ASSUME_TAC THENL
     [ASM_MESON_TAC[VECTOR_CHOOSE_DIST; DIST_SYM; REAL_LT_IMP_LE];
      ASM_MESON_TAC[REAL_NOT_LE; DIST_REFL; DIST_SYM]];
    RULE_ASSUM_TAC(REWRITE_RULE[DIST_NZ]) THEN
    DISCH_THEN(MP_TAC o SPEC `z + ((d / &2) / dist(z,x)) % (z - x:real^N)`) THEN
    REWRITE_TAC[dist; VECTOR_ADD_SUB; NORM_MUL; REAL_ABS_DIV;
                REAL_ABS_NORM; REAL_ABS_NUM] THEN
    ASM_SIMP_TAC[REAL_DIV_RMUL; GSYM dist; REAL_LT_IMP_NZ] THEN
    ASM_SIMP_TAC[REAL_LT_LDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN
    ASM_REWRITE_TAC[REAL_ARITH `abs d < d * &2 <=> &0 < d`] THEN
    DISCH_THEN(ANTE_RES_THEN MP_TAC) THEN REWRITE_TAC[dist] THEN
    REWRITE_TAC[VECTOR_ARITH `x - (z + k % (z - x)) = (&1 + k) % (x - z)`] THEN
    REWRITE_TAC[REAL_NOT_LE; NORM_MUL] THEN
    GEN_REWRITE_TAC LAND_CONV [GSYM REAL_MUL_LID] THEN
    ONCE_REWRITE_TAC[NORM_SUB] THEN
    ASM_SIMP_TAC[REAL_LT_RMUL_EQ; GSYM dist] THEN
    MATCH_MP_TAC(REAL_ARITH `&0 < x ==> &1 < abs(&1 + x)`) THEN
    ONCE_REWRITE_TAC[DIST_SYM] THEN
    ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; ARITH]]);;


let FRONTIER_BALL = 
prove
 (`!a e. &0 < e ==> frontier(ball(a,e)) = sphere(a,e)`,

  SIMP_TAC[frontier; sphere; CLOSURE_BALL; INTERIOR_OPEN; OPEN_BALL;
           REAL_LT_IMP_LE] THEN
  REWRITE_TAC[EXTENSION; IN_DIFF; IN_ELIM_THM; IN_BALL; IN_CBALL] THEN
  REAL_ARITH_TAC);;


let FRONTIER_CBALL = 
prove
 (`!a e. frontier(cball(a,e)) = sphere(a,e)`,

  SIMP_TAC[frontier; sphere; INTERIOR_CBALL; CLOSED_CBALL; CLOSURE_CLOSED;
           REAL_LT_IMP_LE] THEN
  REWRITE_TAC[EXTENSION; IN_DIFF; IN_ELIM_THM; IN_BALL; IN_CBALL] THEN
  REAL_ARITH_TAC);;


let CBALL_EQ_EMPTY = 
prove
 (`!x e. (cball(x,e) = {}) <=> e < &0`,


let CBALL_EMPTY = 
prove
 (`!x e. e < &0 ==> cball(x,e) = {}`,

  REWRITE_TAC[CBALL_EQ_EMPTY]);;


let CBALL_EQ_SING = 
prove
 (`!x:real^N e. (cball(x,e) = {x}) <=> e = &0`,

  REPEAT GEN_TAC THEN REWRITE_TAC[EXTENSION; IN_CBALL; IN_SING] THEN
  EQ_TAC THENL [ALL_TAC; MESON_TAC[DIST_LE_0]] THEN
  DISCH_THEN(fun th -> MP_TAC(SPEC `x + (e / &2) % basis 1:real^N` th) THEN
                       MP_TAC(SPEC `x:real^N` th)) THEN
  REWRITE_TAC[dist; VECTOR_ARITH `x - (x + e):real^N = --e`;
              VECTOR_ARITH `x + e = x <=> e:real^N = vec 0`] THEN
  REWRITE_TAC[NORM_NEG; NORM_MUL; VECTOR_MUL_EQ_0; NORM_0; VECTOR_SUB_REFL] THEN
  SIMP_TAC[NORM_BASIS; BASIS_NONZERO; LE_REFL; DIMINDEX_GE_1] THEN
  REAL_ARITH_TAC);;


let CBALL_SING = 
prove
 (`!x e. e = &0 ==> cball(x,e) = {x}`,

  REWRITE_TAC[CBALL_EQ_SING]);;


let SPHERE_SING = 
prove
 (`!x e. e = &0 ==> sphere(x,e) = {x}`,

  SIMP_TAC[sphere; DIST_EQ_0; SING_GSPEC]);;


let SPHERE_EQ_SING = 
prove
 (`!a:real^N r x. sphere(a,r) = {x} <=> x = a /\ r = &0`,

  REPEAT GEN_TAC THEN EQ_TAC THEN SIMP_TAC[SPHERE_SING] THEN
  ASM_CASES_TAC `r < &0` THEN ASM_SIMP_TAC[SPHERE_EMPTY; NOT_INSERT_EMPTY] THEN
  ASM_CASES_TAC `r = &0` THEN ASM_SIMP_TAC[SPHERE_SING] THENL
   [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC(SET_RULE
   `!y. (x IN s ==> y IN s /\ ~(y = x)) ==> ~(s = {x})`) THEN
  EXISTS_TAC `a - (x - a):real^N` THEN REWRITE_TAC[IN_SPHERE] THEN
  REPEAT(POP_ASSUM MP_TAC) THEN CONV_TAC NORM_ARITH);;

(* ------------------------------------------------------------------------- *)
(* For points in the interior, localization of limits makes no difference.   *)
(* ------------------------------------------------------------------------- *)


let EVENTUALLY_WITHIN_INTERIOR = 
prove
 (`!p s x.
        x IN interior s
        ==> (eventually p (at x within s) <=> eventually p (at x))`,

  REWRITE_TAC[EVENTUALLY_WITHIN; EVENTUALLY_AT; IN_INTERIOR] THEN
  REPEAT GEN_TAC THEN SIMP_TAC[SUBSET; IN_BALL; LEFT_IMP_FORALL_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EQ_TAC THEN DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `min (d:real) e` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  ASM_MESON_TAC[DIST_SYM]);;


let LIM_WITHIN_INTERIOR = 
prove
 (`!f l s x.
        x IN interior s
        ==> ((f --> l) (at x within s) <=> (f --> l) (at x))`,

  SIMP_TAC[tendsto; EVENTUALLY_WITHIN_INTERIOR]);;


let NETLIMIT_WITHIN_INTERIOR = 
prove
 (`!s x:real^N. x IN interior s ==> netlimit(at x within s) = x`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC NETLIMIT_WITHIN THEN
  REWRITE_TAC[TRIVIAL_LIMIT_WITHIN] THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP(REWRITE_RULE[OPEN_CONTAINS_BALL]
   (SPEC_ALL OPEN_INTERIOR))) THEN
  ASM_MESON_TAC[LIMPT_SUBSET; LIMPT_BALL; CENTRE_IN_CBALL; REAL_LT_IMP_LE;
                SUBSET_TRANS; INTERIOR_SUBSET]);;

(* ------------------------------------------------------------------------- *)
(* A non-singleton connected set is perfect (i.e. has no isolated points).   *)
(* ------------------------------------------------------------------------- *)


let CONNECTED_IMP_PERFECT = 
prove
 (`!s x:real^N.
        connected s /\ ~(?a. s = {a}) /\ x IN s ==> x limit_point_of s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[limit_point_of] THEN
  X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THEN
  MATCH_MP_TAC(TAUT `(~p ==> F) ==> p`) THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `x:real^N` o GEN_REWRITE_RULE I
   [OPEN_CONTAINS_CBALL]) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `{x:real^N}` o
    GEN_REWRITE_RULE I [CONNECTED_CLOPEN]) THEN
  REWRITE_TAC[NOT_IMP] THEN REPEAT CONJ_TAC THENL
   [REWRITE_TAC[OPEN_IN_OPEN] THEN EXISTS_TAC `t:real^N->bool` THEN
    ASM SET_TAC[];
    REWRITE_TAC[CLOSED_IN_CLOSED] THEN
    EXISTS_TAC `cball(x:real^N,e)` THEN REWRITE_TAC[CLOSED_CBALL] THEN
    REWRITE_TAC[EXTENSION; IN_INTER; IN_SING] THEN
    ASM_MESON_TAC[CENTRE_IN_CBALL; SUBSET; REAL_LT_IMP_LE];
    ASM SET_TAC[]]);;


let CONNECTED_IMP_PERFECT_CLOSED = 
prove
 (`!s x. connected s /\ closed s /\ ~(?a. s = {a})
         ==> (x limit_point_of s <=> x IN s)`,

(* ------------------------------------------------------------------------- *)
(* Boundedness.                                                              *)
(* ------------------------------------------------------------------------- *)


let bounded = new_definition
  `bounded s <=> ?a. !x:real^N. x IN s ==> norm(x) <= a`;;


let BOUNDED_EMPTY = 
prove
 (`bounded {}`,

  REWRITE_TAC[bounded; NOT_IN_EMPTY]);;


let BOUNDED_SUBSET = 
prove
 (`!s t. bounded t /\ s SUBSET t ==> bounded s`,

  MESON_TAC[bounded; SUBSET]);;


let BOUNDED_INTERIOR = 
prove
 (`!s:real^N->bool. bounded s ==> bounded(interior s)`,


let BOUNDED_CLOSURE = 
prove
 (`!s:real^N->bool. bounded s ==> bounded(closure s)`,

  REWRITE_TAC[bounded; CLOSURE_SEQUENTIAL] THEN
  GEN_TAC THEN MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
  MESON_TAC[REWRITE_RULE[eventually] LIM_NORM_UBOUND;
            TRIVIAL_LIMIT_SEQUENTIALLY; trivial_limit]);;


let BOUNDED_CLOSURE_EQ = 
prove
 (`!s:real^N->bool. bounded(closure s) <=> bounded s`,

  GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[BOUNDED_CLOSURE] THEN
  MESON_TAC[BOUNDED_SUBSET; CLOSURE_SUBSET]);;


let BOUNDED_CBALL = 
prove
 (`!x:real^N e. bounded(cball(x,e))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[bounded] THEN
  EXISTS_TAC `norm(x:real^N) + e` THEN REWRITE_TAC[IN_CBALL; dist] THEN
  NORM_ARITH_TAC);;


let BOUNDED_BALL = 
prove
 (`!x e. bounded(ball(x,e))`,


let FINITE_IMP_BOUNDED = 
prove
 (`!s:real^N->bool. FINITE s ==> bounded s`,

  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN REWRITE_TAC[BOUNDED_EMPTY] THEN
  REWRITE_TAC[bounded; IN_INSERT] THEN X_GEN_TAC `x:real^N` THEN GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 (X_CHOOSE_TAC `B:real`) STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `norm(x:real^N) + abs B` THEN REPEAT STRIP_TAC THEN
  ASM_MESON_TAC[NORM_POS_LE; REAL_ARITH
   `(y <= b /\ &0 <= x ==> y <= x + abs b) /\ x <= x + abs b`]);;


let BOUNDED_UNION = 
prove
 (`!s t. bounded (s UNION t) <=> bounded s /\ bounded t`,

  REWRITE_TAC[bounded; IN_UNION] THEN MESON_TAC[REAL_LE_MAX]);;


let BOUNDED_UNIONS = 
prove
 (`!f. FINITE f /\ (!s. s IN f ==> bounded s) ==> bounded(UNIONS f)`,

  REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  REWRITE_TAC[UNIONS_0; BOUNDED_EMPTY; IN_INSERT; UNIONS_INSERT] THEN
  MESON_TAC[BOUNDED_UNION]);;


let BOUNDED_POS = 
prove
 (`!s. bounded s <=> ?b. &0 < b /\ !x. x IN s ==> norm(x) <= b`,

  REWRITE_TAC[bounded] THEN
  MESON_TAC[REAL_ARITH `&0 < &1 + abs(y) /\ (x <= y ==> x <= &1 + abs(y))`]);;


let BOUNDED_POS_LT = 
prove
 (`!s. bounded s <=> ?b. &0 < b /\ !x. x IN s ==> norm(x) < b`,

  REWRITE_TAC[bounded] THEN
  MESON_TAC[REAL_LT_IMP_LE;
            REAL_ARITH `&0 < &1 + abs(y) /\ (x <= y ==> x < &1 + abs(y))`]);;


let BOUNDED_INTER = 
prove
 (`!s t. bounded s \/ bounded t ==> bounded (s INTER t)`,


let BOUNDED_DIFF = 
prove
 (`!s t. bounded s ==> bounded (s DIFF t)`,

  MESON_TAC[BOUNDED_SUBSET; SUBSET_DIFF]);;


let BOUNDED_INSERT = 
prove
 (`!x s. bounded(x INSERT s) <=> bounded s`,

  ONCE_REWRITE_TAC[SET_RULE `x INSERT s = {x} UNION s`] THEN
  SIMP_TAC[BOUNDED_UNION; FINITE_IMP_BOUNDED; FINITE_RULES]);;


let BOUNDED_SING = 
prove
 (`!a. bounded {a}`,

  REWRITE_TAC[BOUNDED_INSERT; BOUNDED_EMPTY]);;


let BOUNDED_INTERS = 
prove
 (`!f:(real^N->bool)->bool.
        (?s:real^N->bool. s IN f /\ bounded s) ==> bounded(INTERS f)`,

  REWRITE_TAC[LEFT_IMP_EXISTS_THM; IMP_CONJ] THEN REPEAT GEN_TAC THEN
  DISCH_TAC THEN MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] BOUNDED_SUBSET) THEN
  ASM SET_TAC[]);;


let NOT_BOUNDED_UNIV = 
prove
 (`~(bounded (:real^N))`,

  REWRITE_TAC[BOUNDED_POS; NOT_FORALL_THM; NOT_EXISTS_THM; IN_UNIV;
              DE_MORGAN_THM; REAL_NOT_LE] THEN
  X_GEN_TAC `B:real` THEN ASM_CASES_TAC `&0 < B` THEN ASM_REWRITE_TAC[] THEN
  MP_TAC(SPEC `B + &1` VECTOR_CHOOSE_SIZE) THEN
  ASM_SIMP_TAC[REAL_ARITH `&0 < B ==> &0 <= B + &1`] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REAL_ARITH_TAC);;


let COBOUNDED_IMP_UNBOUNDED = 
prove
 (`!s. bounded((:real^N) DIFF s) ==> ~bounded s`,

  GEN_TAC THEN REWRITE_TAC[TAUT `a ==> ~b <=> ~(a /\ b)`] THEN
  REWRITE_TAC[GSYM BOUNDED_UNION; SET_RULE `UNIV DIFF s UNION s = UNIV`] THEN
  REWRITE_TAC[NOT_BOUNDED_UNIV]);;


let BOUNDED_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s. bounded s /\ linear f ==> bounded(IMAGE f s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[BOUNDED_POS] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (X_CHOOSE_TAC `B1:real`) MP_TAC) THEN
  DISCH_THEN(X_CHOOSE_TAC `B2:real` o MATCH_MP LINEAR_BOUNDED_POS) THEN
  EXISTS_TAC `B2 * B1` THEN ASM_SIMP_TAC[REAL_LT_MUL; FORALL_IN_IMAGE] THEN
  X_GEN_TAC `x:real^M` THEN STRIP_TAC THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `B2 * norm(x:real^M)` THEN
  ASM_SIMP_TAC[REAL_LE_LMUL_EQ]);;


let BOUNDED_LINEAR_IMAGE_EQ = 
prove
 (`!f s. linear f /\ (!x y. f x = f y ==> x = y)
         ==> (bounded (IMAGE f s) <=> bounded s)`,

  MATCH_ACCEPT_TAC(LINEAR_INVARIANT_RULE BOUNDED_LINEAR_IMAGE));;

add_linear_invariants [BOUNDED_LINEAR_IMAGE_EQ];;


let BOUNDED_SCALING = 
prove
 (`!c s. bounded s ==> bounded (IMAGE (\x. c % x) s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC BOUNDED_LINEAR_IMAGE THEN
  ASM_SIMP_TAC[LINEAR_COMPOSE_CMUL; LINEAR_ID]);;


let BOUNDED_NEGATIONS = 
prove
 (`!s. bounded s ==> bounded (IMAGE (--) s)`,

  GEN_TAC THEN
  DISCH_THEN(MP_TAC o SPEC `-- &1` o MATCH_MP BOUNDED_SCALING) THEN
  REWRITE_TAC[bounded; IN_IMAGE; VECTOR_MUL_LNEG; VECTOR_MUL_LID]);;


let BOUNDED_TRANSLATION = 
prove
 (`!a:real^N s. bounded s ==> bounded (IMAGE (\x. a + x) s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[BOUNDED_POS; FORALL_IN_IMAGE] THEN
  DISCH_THEN(X_CHOOSE_TAC `B:real`) THEN
  EXISTS_TAC `B + norm(a:real^N)` THEN POP_ASSUM MP_TAC THEN
  MATCH_MP_TAC MONO_AND THEN CONJ_TAC THENL [NORM_ARITH_TAC; ALL_TAC] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN
  REWRITE_TAC[] THEN NORM_ARITH_TAC);;


let BOUNDED_TRANSLATION_EQ = 
prove
 (`!a s. bounded (IMAGE (\x:real^N. a + x) s) <=> bounded s`,

  REPEAT GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[BOUNDED_TRANSLATION] THEN
  DISCH_THEN(MP_TAC o SPEC `--a:real^N` o MATCH_MP BOUNDED_TRANSLATION) THEN
  REWRITE_TAC[GSYM IMAGE_o; o_DEF; IMAGE_ID;
              VECTOR_ARITH `--a + a + x:real^N = x`]);;

add_translation_invariants [BOUNDED_TRANSLATION_EQ];;


let BOUNDED_DIFFS = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t ==> bounded {x - y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[BOUNDED_POS] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_TAC `B:real`) (X_CHOOSE_TAC `C:real`)) THEN
  EXISTS_TAC `B + C:real` THEN REWRITE_TAC[IN_ELIM_THM] THEN
  CONJ_TAC THENL [ASM_REAL_ARITH_TAC; REPEAT STRIP_TAC] THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC(NORM_ARITH
   `norm x <= a /\ norm y <= b ==> norm(x - y) <= a + b`) THEN
  ASM_SIMP_TAC[]);;


let BOUNDED_SUMS = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t ==> bounded {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[BOUNDED_POS] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_TAC `B:real`) (X_CHOOSE_TAC `C:real`)) THEN
  EXISTS_TAC `B + C:real` THEN REWRITE_TAC[IN_ELIM_THM] THEN
  CONJ_TAC THENL [ASM_REAL_ARITH_TAC; REPEAT STRIP_TAC] THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC(NORM_ARITH
   `norm x <= a /\ norm y <= b ==> norm(x + y) <= a + b`) THEN
  ASM_SIMP_TAC[]);;


let BOUNDED_SUMS_IMAGE = 
prove
 (`!f g t. bounded {f x | x IN t} /\ bounded {g x | x IN t}
           ==> bounded {f x + g x | x IN t}`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP BOUNDED_SUMS) THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] BOUNDED_SUBSET) THEN
  SET_TAC[]);;


let BOUNDED_SUMS_IMAGES = 
prove
 (`!f:A->B->real^N t s.
        FINITE s /\
        (!a. a IN s ==> bounded {f x a | x IN t})
        ==> bounded { vsum s (f x) | x IN t}`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  SIMP_TAC[VSUM_CLAUSES] THEN CONJ_TAC THENL
   [DISCH_THEN(K ALL_TAC) THEN MATCH_MP_TAC BOUNDED_SUBSET THEN
    EXISTS_TAC `{vec 0:real^N}` THEN
    SIMP_TAC[FINITE_IMP_BOUNDED; FINITE_RULES] THEN SET_TAC[];
    ALL_TAC] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC BOUNDED_SUMS_IMAGE THEN
  ASM_SIMP_TAC[IN_INSERT]);;


let BOUNDED_SUBSET_BALL = 
prove
 (`!s x:real^N. bounded(s) ==> ?r. &0 < r /\ s SUBSET ball(x,r)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[BOUNDED_POS] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `&2 * B + norm(x:real^N)` THEN
  ASM_SIMP_TAC[NORM_POS_LE; REAL_ARITH
    `&0 < B /\ &0 <= x ==> &0 < &2 * B + x`] THEN
  REWRITE_TAC[SUBSET] THEN X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN ASM_REWRITE_TAC[IN_BALL] THEN
  UNDISCH_TAC `&0 < B` THEN NORM_ARITH_TAC);;


let BOUNDED_SUBSET_CBALL = 
prove
 (`!s x:real^N. bounded(s) ==> ?r. &0 < r /\ s SUBSET cball(x,r)`,


let UNBOUNDED_INTER_COBOUNDED = 
prove
 (`!s t. ~bounded s /\ bounded((:real^N) DIFF t) ==> ~(s INTER t = {})`,

  REWRITE_TAC[SET_RULE `s INTER t = {} <=> s SUBSET (:real^N) DIFF t`] THEN
  MESON_TAC[BOUNDED_SUBSET]);;


let COBOUNDED_INTER_UNBOUNDED = 
prove
 (`!s t. bounded((:real^N) DIFF s) /\ ~bounded t ==> ~(s INTER t = {})`,

  REWRITE_TAC[SET_RULE `s INTER t = {} <=> t SUBSET (:real^N) DIFF s`] THEN
  MESON_TAC[BOUNDED_SUBSET]);;


let SUBSPACE_BOUNDED_EQ_TRIVIAL = 
prove
 (`!s:real^N->bool. subspace s ==> (bounded s <=> s = {vec 0})`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN SIMP_TAC[BOUNDED_SING] THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE
   `~(s = {a}) ==> a IN s ==> ?b. b IN s /\ ~(b = a)`)) THEN
  ASM_SIMP_TAC[SUBSPACE_0] THEN
  DISCH_THEN(X_CHOOSE_THEN `v:real^N` STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[bounded; NOT_EXISTS_THM] THEN X_GEN_TAC `B:real` THEN
  DISCH_THEN(MP_TAC o SPEC `(B + &1) / norm v % v:real^N`) THEN
  ASM_SIMP_TAC[SUBSPACE_MUL; NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM] THEN
  ASM_SIMP_TAC[REAL_DIV_RMUL; NORM_EQ_0] THEN REAL_ARITH_TAC);;


let BOUNDED_COMPONENTWISE = 
prove
 (`!s:real^N->bool.
        bounded s <=> !i. 1 <= i /\ i <= dimindex(:N)
                          ==> bounded (IMAGE (\x. lift(x$i)) s)`,

  GEN_TAC THEN REWRITE_TAC[BOUNDED_POS; FORALL_IN_IMAGE; NORM_LIFT] THEN
  EQ_TAC THENL [ASM_MESON_TAC[COMPONENT_LE_NORM; REAL_LE_TRANS]; ALL_TAC] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  SIMP_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `b:num->real` THEN
  DISCH_TAC THEN EXISTS_TAC `sum(1..dimindex(:N)) b` THEN CONJ_TAC THENL
   [MATCH_MP_TAC REAL_LET_TRANS THEN
    EXISTS_TAC `sum(1..dimindex(:N)) (\i. &0)` THEN
    SIMP_TAC[SUM_POS_LE_NUMSEG; REAL_POS] THEN
    MATCH_MP_TAC SUM_LT_ALL THEN
    ASM_SIMP_TAC[IN_NUMSEG; FINITE_NUMSEG; NUMSEG_EMPTY] THEN
    REWRITE_TAC[NOT_LT; DIMINDEX_GE_1];
    REPEAT STRIP_TAC THEN
    W(MP_TAC o PART_MATCH lhand NORM_LE_L1 o lhand o snd) THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] REAL_LE_TRANS) THEN
    MATCH_MP_TAC SUM_LE THEN ASM_SIMP_TAC[IN_NUMSEG; FINITE_NUMSEG]]);;

(* ------------------------------------------------------------------------- *)
(* Some theorems on sups and infs using the notion "bounded".                *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_LIFT = 
prove
 (`!s. bounded(IMAGE lift s) <=>  ?a. !x. x IN s ==> abs(x) <= a`,

  REWRITE_TAC[bounded; FORALL_LIFT; NORM_LIFT; LIFT_IN_IMAGE_LIFT]);;


let BOUNDED_HAS_SUP = 
prove
 (`!s. bounded(IMAGE lift s) /\ ~(s = {})
       ==> (!x. x IN s ==> x <= sup s) /\
           (!b. (!x. x IN s ==> x <= b) ==> sup s <= b)`,

  REWRITE_TAC[BOUNDED_LIFT; IMAGE_EQ_EMPTY] THEN
  MESON_TAC[SUP; REAL_ARITH `abs(x) <= a ==> x <= a`]);;


let SUP_INSERT = 
prove
 (`!x s. bounded (IMAGE lift s)
         ==> sup(x INSERT s) = if s = {} then x else max x (sup s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC REAL_SUP_UNIQUE THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[IN_SING] THENL
   [MESON_TAC[REAL_LE_REFL]; ALL_TAC] THEN
  REWRITE_TAC[REAL_LE_MAX; REAL_LT_MAX; IN_INSERT] THEN
  MP_TAC(ISPEC `s:real->bool` BOUNDED_HAS_SUP) THEN ASM_REWRITE_TAC[] THEN
  REPEAT STRIP_TAC THEN ASM_MESON_TAC[REAL_LE_REFL; REAL_NOT_LT]);;


let BOUNDED_HAS_INF = 
prove
 (`!s. bounded(IMAGE lift s) /\ ~(s = {})
       ==> (!x. x IN s ==> inf s <= x) /\
           (!b. (!x. x IN s ==> b <= x) ==> b <= inf s)`,

  REWRITE_TAC[BOUNDED_LIFT; IMAGE_EQ_EMPTY] THEN
  MESON_TAC[INF; REAL_ARITH `abs(x) <= a ==> --a <= x`]);;


let INF_INSERT = 
prove
 (`!x s. bounded (IMAGE lift s)
         ==> inf(x INSERT s) = if s = {} then x else min x (inf s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC REAL_INF_UNIQUE THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[IN_SING] THENL
   [MESON_TAC[REAL_LE_REFL]; ALL_TAC] THEN
  REWRITE_TAC[REAL_MIN_LE; REAL_MIN_LT; IN_INSERT] THEN
  MP_TAC(ISPEC `s:real->bool` BOUNDED_HAS_INF) THEN ASM_REWRITE_TAC[] THEN
  REPEAT STRIP_TAC THEN ASM_MESON_TAC[REAL_LE_REFL; REAL_NOT_LT]);;

(* ------------------------------------------------------------------------- *)
(* Subset and overlapping relations on balls.                                *)
(* ------------------------------------------------------------------------- *)


let SUBSET_BALLS = 
prove
 (`(!a a':real^N r r'.
      ball(a,r) SUBSET ball(a',r') <=> dist(a,a') + r <= r' \/ r <= &0) /\
   (!a a':real^N r r'.
      ball(a,r) SUBSET cball(a',r') <=> dist(a,a') + r <= r' \/ r <= &0) /\
   (!a a':real^N r r'.
      cball(a,r) SUBSET ball(a',r') <=> dist(a,a') + r < r' \/ r < &0) /\
   (!a a':real^N r r'.
      cball(a,r) SUBSET cball(a',r') <=> dist(a,a') + r <= r' \/ r < &0)`,

  
let lemma = prove
   (`(!a':real^N r r'.
       cball(a,r) SUBSET cball(a',r') <=> dist(a,a') + r <= r' \/ r < &0) /\
     (!a':real^N r r'.
       cball(a,r) SUBSET ball(a',r') <=> dist(a,a') + r < r' \/ r < &0)`,
    CONJ_TAC THEN
    (GEOM_ORIGIN_TAC `a':real^N` THEN
    REPEAT GEN_TAC THEN REWRITE_TAC[SUBSET; IN_CBALL; IN_BALL] THEN
    EQ_TAC THENL [REWRITE_TAC[DIST_0]; NORM_ARITH_TAC] THEN
    DISJ_CASES_TAC(REAL_ARITH `r < &0 \/ &0 <= r`) THEN
    ASM_REWRITE_TAC[] THEN DISCH_TAC THEN DISJ1_TAC THEN
    ASM_CASES_TAC `a:real^N = vec 0` THENL
     [FIRST_X_ASSUM(MP_TAC o SPEC `r % basis 1:real^N`) THEN
      ASM_SIMP_TAC[DIST_0; NORM_MUL; NORM_BASIS; DIMINDEX_GE_1; LE_REFL];
      FIRST_X_ASSUM(MP_TAC o SPEC `(&1 + r / norm(a)) % a:real^N`) THEN
      SIMP_TAC[dist; VECTOR_ARITH `a - (&1 + x) % a:real^N = --(x % a)`] THEN
      ASM_SIMP_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM; NORM_NEG; REAL_POS;
                   REAL_LE_DIV; NORM_POS_LE; REAL_ADD_RDISTRIB; REAL_DIV_RMUL;
               NORM_EQ_0; REAL_ARITH `&0 <= x ==> abs(&1 + x) = &1 + x`]] THEN
    UNDISCH_TAC `&0 <= r` THEN NORM_ARITH_TAC))
  and tac = DISCH_THEN(MP_TAC o MATCH_MP SUBSET_CLOSURE) THEN
            ASM_SIMP_TAC[CLOSED_CBALL; CLOSURE_CLOSED; CLOSURE_BALL] in
  REWRITE_TAC[AND_FORALL_THM] THEN GEOM_ORIGIN_TAC `a':real^N` THEN
  REPEAT STRIP_TAC THEN
  (EQ_TAC THENL
    [ALL_TAC; REWRITE_TAC[SUBSET; IN_BALL; IN_CBALL] THEN NORM_ARITH_TAC]) THEN
  MATCH_MP_TAC(SET_RULE
   `(s = {} <=> q) /\ (s SUBSET t /\ ~(s = {}) /\ ~(t = {}) ==> p)
    ==> s SUBSET t ==> p \/ q`) THEN
  REWRITE_TAC[BALL_EQ_EMPTY; CBALL_EQ_EMPTY; REAL_NOT_LE; REAL_NOT_LT] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC STRIP_ASSUME_TAC) THENL
   [tac; tac; ALL_TAC; ALL_TAC] THEN REWRITE_TAC[lemma] THEN
  REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC);;


let INTER_BALLS_EQ_EMPTY = 
prove
 (`(!a b:real^N r s. ball(a,r) INTER ball(b,s) = {} <=>
                     r <= &0 \/ s <= &0 \/ r + s <= dist(a,b)) /\
   (!a b:real^N r s. ball(a,r) INTER cball(b,s) = {} <=>
                     r <= &0 \/ s < &0 \/ r + s <= dist(a,b)) /\
   (!a b:real^N r s. cball(a,r) INTER ball(b,s) = {} <=>
                     r < &0 \/ s <= &0 \/ r + s <= dist(a,b)) /\
   (!a b:real^N r s. cball(a,r) INTER cball(b,s) = {} <=>
                     r < &0 \/ s < &0 \/ r + s < dist(a,b))`,

  REPEAT STRIP_TAC THEN GEOM_ORIGIN_TAC `a:real^N` THEN
  GEOM_BASIS_MULTIPLE_TAC 1 `b:real^N` THEN REPEAT STRIP_TAC THEN
  REWRITE_TAC[EXTENSION; NOT_IN_EMPTY; IN_INTER; IN_CBALL; IN_BALL] THEN
  (EQ_TAC THENL
    [ALL_TAC;
     SPEC_TAC(`b % basis 1:real^N`,`v:real^N`) THEN CONV_TAC NORM_ARITH]) THEN
  DISCH_THEN(MP_TAC o GEN `c:real` o SPEC `c % basis 1:real^N`) THEN
  SIMP_TAC[NORM_MUL; NORM_BASIS; LE_REFL; DIMINDEX_GE_1; dist; NORM_NEG;
           VECTOR_SUB_LZERO; GSYM VECTOR_SUB_RDISTRIB; REAL_MUL_RID] THEN
  ASM_REWRITE_TAC[real_abs] THEN REWRITE_TAC[GSYM real_abs] THEN
  DISCH_THEN(fun th ->
    MP_TAC(SPEC `min b r:real` th) THEN
    MP_TAC(SPEC `max (&0) (b - s:real)` th) THEN
    MP_TAC(SPEC `(r + (b - s)) / &2` th)) THEN
  ASM_REAL_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Every closed set is a G_Delta.                                            *)
(* ------------------------------------------------------------------------- *)


let CLOSED_AS_GDELTA = 
prove
 (`!s:real^N->bool.
        closed s
        ==> ?g. COUNTABLE g /\
                (!u. u IN g ==> open u) /\
                INTERS g = s`,

  REPEAT STRIP_TAC THEN EXISTS_TAC
   `{ UNIONS { ball(x:real^N,inv(&n + &1)) | x IN s} | n IN (:num)}` THEN
  SIMP_TAC[SIMPLE_IMAGE; COUNTABLE_IMAGE; NUM_COUNTABLE] THEN
  SIMP_TAC[FORALL_IN_IMAGE; OPEN_UNIONS; OPEN_BALL] THEN
  MATCH_MP_TAC(SET_RULE
   `closure s = s /\ s SUBSET t /\ t SUBSET closure s
    ==> t = s`) THEN
  ASM_REWRITE_TAC[CLOSURE_EQ] THEN CONJ_TAC THENL
   [REWRITE_TAC[SUBSET_INTERS; FORALL_IN_IMAGE; IN_UNIV] THEN
    X_GEN_TAC `n:num` THEN REWRITE_TAC[UNIONS_IMAGE; SUBSET; IN_ELIM_THM] THEN
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN EXISTS_TAC `x:real^N` THEN
    ASM_REWRITE_TAC[CENTRE_IN_BALL; REAL_LT_INV_EQ] THEN REAL_ARITH_TAC;
    REWRITE_TAC[SUBSET; CLOSURE_APPROACHABLE; INTERS_IMAGE; IN_UNIV] THEN
    X_GEN_TAC `x:real^N` THEN REWRITE_TAC[IN_ELIM_THM; UNIONS_IMAGE] THEN
    DISCH_TAC THEN X_GEN_TAC `e:real` THEN  DISCH_TAC THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [REAL_ARCH_INV]) THEN
    DISCH_THEN(X_CHOOSE_THEN `n:num` STRIP_ASSUME_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `n:num`) THEN REWRITE_TAC[IN_BALL] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `y:real^N` THEN
    MATCH_MP_TAC MONO_AND THEN REWRITE_TAC[] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] REAL_LT_TRANS) THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT]
        REAL_LT_TRANS)) THEN
    MATCH_MP_TAC REAL_LT_INV2 THEN
    REWRITE_TAC[REAL_OF_NUM_ADD; REAL_OF_NUM_LT] THEN ASM_ARITH_TAC]);;

(* ------------------------------------------------------------------------- *)
(* Compactness (the definition is the one based on convegent subsequences).  *)
(* ------------------------------------------------------------------------- *)


let compact = new_definition
  `compact s <=>
        !f:num->real^N.
            (!n. f(n) IN s)
            ==> ?l r. l IN s /\ (!m n:num. m < n ==> r(m) < r(n)) /\
                      ((f o r) --> l) sequentially`;;


let MONOTONE_BIGGER = 
prove
 (`!r. (!m n. m < n ==> r(m) < r(n)) ==> !n:num. n <= r(n)`,

  GEN_TAC THEN DISCH_TAC THEN INDUCT_TAC THEN
  ASM_MESON_TAC[LE_0; ARITH_RULE `n <= m /\ m < p ==> SUC n <= p`; LT]);;


let LIM_SUBSEQUENCE = 
prove
 (`!s r l. (!m n. m < n ==> r(m) < r(n)) /\ (s --> l) sequentially
           ==> (s o r --> l) sequentially`,

  REWRITE_TAC[LIM_SEQUENTIALLY; o_THM] THEN
  MESON_TAC[MONOTONE_BIGGER; LE_TRANS]);;


let MONOTONE_SUBSEQUENCE = 
prove
 (`!s:num->real. ?r:num->num.
           (!m n. m < n ==> r(m) < r(n)) /\
           ((!m n. m <= n ==> s(r(m)) <= s(r(n))) \/
            (!m n. m <= n ==> s(r(n)) <= s(r(m))))`,

  GEN_TAC THEN
  ASM_CASES_TAC `!n:num. ?p. n < p /\ !m. p <= m ==> s(m) <= s(p)` THEN
  POP_ASSUM MP_TAC THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_EXISTS_THM; NOT_IMP; DE_MORGAN_THM] THEN
  REWRITE_TAC[RIGHT_OR_EXISTS_THM; SKOLEM_THM; REAL_NOT_LE; REAL_NOT_LT] THENL
   [ABBREV_TAC `N = 0`; DISCH_THEN(X_CHOOSE_THEN `N:num` MP_TAC)] THEN
  DISCH_THEN(X_CHOOSE_THEN `next:num->num` STRIP_ASSUME_TAC) THEN
  (MP_TAC o prove_recursive_functions_exist num_RECURSION)
   `(r 0 = next(SUC N)) /\ (!n. r(SUC n) = next(r n))` THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN STRIP_TAC THENL
   [SUBGOAL_THEN `!m:num n:num. r n <= m ==> s(m) <= s(r n):real`
    ASSUME_TAC THEN TRY CONJ_TAC THEN TRY DISJ2_TAC THEN
    GEN_TAC THEN INDUCT_TAC THEN ASM_REWRITE_TAC[LT; LE] THEN
    ASM_MESON_TAC[REAL_LE_TRANS; REAL_LE_REFL; LT_IMP_LE; LT_TRANS];
    SUBGOAL_THEN `!n. N < (r:num->num) n` ASSUME_TAC THEN
    TRY(CONJ_TAC THENL [GEN_TAC; DISJ1_TAC THEN GEN_TAC]) THEN
    INDUCT_TAC THEN ASM_REWRITE_TAC[LT; LE] THEN
    TRY STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_MESON_TAC[REAL_LT_REFL; LT_LE; LTE_TRANS; REAL_LE_REFL;
                  REAL_LT_LE; REAL_LE_TRANS; LT]]);;


let CONVERGENT_BOUNDED_INCREASING = 
prove
 (`!s:num->real b. (!m n. m <= n ==> s m <= s n) /\ (!n. abs(s n) <= b)
                   ==> ?l. !e. &0 < e ==> ?N. !n. N <= n ==> abs(s n - l) < e`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPEC `\x. ?n. (s:num->real) n = x` REAL_COMPLETE) THEN
  REWRITE_TAC[] THEN ANTS_TAC THENL
   [ASM_MESON_TAC[REAL_ARITH `abs(x) <= b ==> x <= b`]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `l:real` THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `l - e`) THEN
  ASM_MESON_TAC[REAL_ARITH `&0 < e ==> ~(l <= l - e)`;
      REAL_ARITH `x <= y /\ y <= l /\ ~(x <= l - e) ==> abs(y - l) < e`]);;


let CONVERGENT_BOUNDED_MONOTONE = 
prove
 (`!s:num->real b. (!n. abs(s n) <= b) /\
                   ((!m n. m <= n ==> s m <= s n) \/
                    (!m n. m <= n ==> s n <= s m))
                   ==> ?l. !e. &0 < e ==> ?N. !n. N <= n ==> abs(s n - l) < e`,

  REPEAT STRIP_TAC THENL
   [ASM_MESON_TAC[CONVERGENT_BOUNDED_INCREASING]; ALL_TAC] THEN
  MP_TAC(SPEC `\n. --((s:num->real) n)` CONVERGENT_BOUNDED_INCREASING) THEN
  ASM_REWRITE_TAC[REAL_LE_NEG2; REAL_ABS_NEG] THEN
  ASM_MESON_TAC[REAL_ARITH `abs(x - --l) = abs(--x - l)`]);;


let COMPACT_REAL_LEMMA = 
prove
 (`!s b. (!n:num. abs(s n) <= b)
         ==> ?l r. (!m n:num. m < n ==> r(m) < r(n)) /\
                   !e. &0 < e ==> ?N. !n. N <= n ==> abs(s(r n) - l) < e`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN
  MP_TAC(SPEC `s:num->real` MONOTONE_SUBSEQUENCE) THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN DISCH_TAC THEN ASM_SIMP_TAC[] THEN
  MATCH_MP_TAC CONVERGENT_BOUNDED_MONOTONE THEN ASM_MESON_TAC[]);;


let COMPACT_LEMMA = 
prove
 (`!s. bounded s /\ (!n. (x:num->real^N) n IN s)
       ==> !d. d <= dimindex(:N)
               ==> ?l:real^N r. (!m n. m < n ==> r m < (r:num->num) n) /\
                         !e. &0 < e
                             ==> ?N. !n i. 1 <= i /\ i <= d
                                           ==> N <= n
                                               ==> abs(x(r n)$i - l$i) < e`,

  GEN_TAC THEN REWRITE_TAC[bounded] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (X_CHOOSE_TAC `b:real`) ASSUME_TAC) THEN
  INDUCT_TAC THENL
   [REWRITE_TAC[ARITH_RULE `1 <= i /\ i <= 0 <=> F`; CONJ_ASSOC] THEN
    DISCH_TAC THEN EXISTS_TAC `\n:num. n` THEN REWRITE_TAC[];
    ALL_TAC] THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o check (is_imp o concl)) THEN
  ASM_SIMP_TAC[ARITH_RULE `SUC d <= n ==> d <= n`] THEN STRIP_TAC THEN
  MP_TAC(SPECL [`\n:num. (x:num->real^N) (r n) $ (SUC d)`; `b:real`]
         COMPACT_REAL_LEMMA) THEN
  REWRITE_TAC[] THEN ANTS_TAC THENL
   [ASM_MESON_TAC[REAL_LE_TRANS; COMPONENT_LE_NORM; ARITH_RULE `1 <= SUC n`];
    ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `y:real` (X_CHOOSE_THEN `s:num->num`
        STRIP_ASSUME_TAC)) THEN
  MAP_EVERY EXISTS_TAC
   [`(lambda k. if k = SUC d then y else (l:real^N)$k):real^N`;
    `(r:num->num) o (s:num->num)`] THEN
  ASM_SIMP_TAC[o_THM] THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  REPEAT(FIRST_ASSUM(C UNDISCH_THEN (MP_TAC o SPEC `e:real`) o concl)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(X_CHOOSE_TAC `N1:num`) THEN
  DISCH_THEN(X_CHOOSE_TAC `N2:num`) THEN EXISTS_TAC `N1 + N2:num` THEN
  FIRST_ASSUM(fun th -> SIMP_TAC[LAMBDA_BETA; MATCH_MP(ARITH_RULE
   `SUC d <= n ==> !i. 1 <= i /\ i <= SUC d ==> 1 <= i /\ i <= n`) th]) THEN
  REWRITE_TAC[LE] THEN REPEAT STRIP_TAC THEN
  ASM_REWRITE_TAC[] THEN TRY COND_CASES_TAC THEN
  ASM_MESON_TAC[MONOTONE_BIGGER; LE_TRANS;
    ARITH_RULE `N1 + N2 <= n ==> N2 <= n:num /\ N1 <= n`;
    ARITH_RULE `1 <= i /\ i <= d /\ SUC d <= n
                ==> ~(i = SUC d) /\ 1 <= SUC d /\ d <= n /\ i <= n`]);;


let BOUNDED_CLOSED_IMP_COMPACT = 
prove
 (`!s:real^N->bool. bounded s /\ closed s ==> compact s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[compact] THEN
  X_GEN_TAC `x:num->real^N` THEN DISCH_TAC THEN
  MP_TAC(ISPEC `s:real^N->bool` COMPACT_LEMMA) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o SPEC `dimindex(:N)`) THEN
  REWRITE_TAC[LE_REFL] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `l:real^N` THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `r:num->num` THEN ASM_SIMP_TAC[] THEN
  STRIP_TAC THEN MATCH_MP_TAC(TAUT `(b ==> a) /\ b ==> a /\ b`) THEN
  REPEAT STRIP_TAC THENL
   [FIRST_ASSUM(MATCH_MP_TAC o REWRITE_RULE[CLOSED_SEQUENTIAL_LIMITS]) THEN
    EXISTS_TAC `(x:num->real^N) o (r:num->num)` THEN
    ASM_REWRITE_TAC[o_THM];
    ALL_TAC] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY] THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2 / &(dimindex(:N))`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; DIMINDEX_NONZERO;
               REAL_HALF; ARITH_RULE `0 < n <=> ~(n = 0)`] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  REWRITE_TAC[dist] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC(MATCH_MP (REAL_ARITH `a <= b ==> b < e ==> a < e`)
                        (SPEC_ALL NORM_LE_L1)) THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `sum (1..dimindex(:N))
                  (\k. e / &2 / &(dimindex(:N)))` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC SUM_LE_NUMSEG THEN
    SIMP_TAC[o_THM; LAMBDA_BETA; vector_sub] THEN
    ASM_MESON_TAC[REAL_LT_IMP_LE; LE_TRANS];
    ASM_SIMP_TAC[SUM_CONST_NUMSEG; ADD_SUB; REAL_DIV_LMUL; REAL_OF_NUM_EQ;
                 DIMINDEX_NONZERO; REAL_LE_REFL; REAL_LT_LDIV_EQ; ARITH;
                 REAL_OF_NUM_LT; REAL_ARITH `x < x * &2 <=> &0 < x`]]);;

(* ------------------------------------------------------------------------- *)
(* Completeness.                                                             *)
(* ------------------------------------------------------------------------- *)


let cauchy = new_definition
  `cauchy (s:num->real^N) <=>
     !e. &0 < e ==> ?N. !m n. m >= N /\ n >= N ==> dist(s m,s n) < e`;;


let complete = new_definition
  `complete s <=>
     !f:num->real^N. (!n. f n IN s) /\ cauchy f
                      ==> ?l. l IN s /\ (f --> l) sequentially`;;


let CAUCHY = 
prove
 (`!s:num->real^N.
      cauchy s <=> !e. &0 < e ==> ?N. !n. n >= N ==> dist(s n,s N) < e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[cauchy; GE] THEN EQ_TAC THENL
   [MESON_TAC[LE_REFL]; DISCH_TAC] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  MESON_TAC[DIST_TRIANGLE_HALF_L]);;


let CONVERGENT_IMP_CAUCHY = 
prove
 (`!s l. (s --> l) sequentially ==> cauchy s`,

  REWRITE_TAC[LIM_SEQUENTIALLY; cauchy] THEN
  REPEAT GEN_TAC THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; ARITH] THEN
  ASM_MESON_TAC[GE; LE_REFL; DIST_TRIANGLE_HALF_L]);;


let CAUCHY_IMP_BOUNDED = 
prove
 (`!s:num->real^N. cauchy s ==> bounded {y | ?n. y = s n}`,

  REWRITE_TAC[cauchy; bounded; IN_ELIM_THM] THEN GEN_TAC THEN
  DISCH_THEN(MP_TAC o SPEC `&1`) THEN REWRITE_TAC[REAL_LT_01] THEN
  DISCH_THEN(X_CHOOSE_THEN `N:num` (MP_TAC o SPEC `N:num`)) THEN
  REWRITE_TAC[GE_REFL] THEN DISCH_TAC THEN
  SUBGOAL_THEN `!n:num. N <= n ==> norm(s n :real^N) <= norm(s N) + &1`
  ASSUME_TAC THENL
   [ASM_MESON_TAC[GE; dist; DIST_SYM; NORM_TRIANGLE_SUB;
                  REAL_ARITH `a <= b + c /\ c < &1 ==> a <= b + &1`];
    MP_TAC(ISPECL [`\n:num. norm(s n :real^N)`; `0..N`]
                  UPPER_BOUND_FINITE_SET_REAL) THEN
    SIMP_TAC[FINITE_NUMSEG; IN_NUMSEG; LE_0; LEFT_IMP_EXISTS_THM] THEN
    ASM_MESON_TAC[LE_CASES;
                  REAL_ARITH `x <= a \/ x <= b ==> x <= abs a + abs b`]]);;


let COMPACT_IMP_COMPLETE = 
prove
 (`!s:real^N->bool. compact s ==> complete s`,

  GEN_TAC THEN REWRITE_TAC[complete; compact] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `f:num->real^N` THEN
  DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `r:num->num` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ] LIM_ADD)) THEN
  DISCH_THEN(MP_TAC o SPEC `\n. (f:num->real^N)(n) - f(r n)`) THEN
  DISCH_THEN(MP_TAC o SPEC `vec 0: real^N`) THEN ASM_REWRITE_TAC[o_THM] THEN
  REWRITE_TAC[VECTOR_ADD_RID; VECTOR_SUB_ADD2; ETA_AX] THEN
  DISCH_THEN MATCH_MP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [cauchy]) THEN
  REWRITE_TAC[GE; LIM; SEQUENTIALLY; dist; VECTOR_SUB_RZERO] THEN
  SUBGOAL_THEN `!n:num. n <= r(n)` MP_TAC THENL [INDUCT_TAC; ALL_TAC] THEN
  ASM_MESON_TAC[ LE_TRANS; LE_REFL; LT; LET_TRANS; LE_0; LE_SUC_LT]);;


let COMPLETE_UNIV = 
prove
 (`complete(:real^N)`,

  REWRITE_TAC[complete; IN_UNIV] THEN X_GEN_TAC `x:num->real^N` THEN
  DISCH_TAC THEN FIRST_ASSUM(MP_TAC o MATCH_MP CAUCHY_IMP_BOUNDED) THEN
  DISCH_THEN(ASSUME_TAC o MATCH_MP BOUNDED_CLOSURE) THEN
  MP_TAC(ISPEC `closure {y:real^N | ?n:num. y = x n}`
               COMPACT_IMP_COMPLETE) THEN
  ASM_SIMP_TAC[BOUNDED_CLOSED_IMP_COMPACT; CLOSED_CLOSURE; complete] THEN
  DISCH_THEN(MP_TAC o SPEC `x:num->real^N`) THEN
  ANTS_TAC THENL [ALL_TAC; MESON_TAC[]] THEN
  ASM_REWRITE_TAC[closure; IN_ELIM_THM; IN_UNION] THEN MESON_TAC[]);;


let COMPLETE_EQ_CLOSED = 
prove
 (`!s:real^N->bool. complete s <=> closed s`,

  GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[complete; CLOSED_LIMPT; LIMPT_SEQUENTIAL] THEN
    REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN GEN_TAC THEN
    REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN MATCH_MP_TAC MONO_FORALL THEN
    MESON_TAC[CONVERGENT_IMP_CAUCHY; IN_DELETE; LIM_UNIQUE;
              TRIVIAL_LIMIT_SEQUENTIALLY];
    REWRITE_TAC[complete; CLOSED_SEQUENTIAL_LIMITS] THEN DISCH_TAC THEN
    X_GEN_TAC `f:num->real^N` THEN STRIP_TAC THEN
    MP_TAC(REWRITE_RULE[complete] COMPLETE_UNIV) THEN
    DISCH_THEN(MP_TAC o SPEC `f:num->real^N`) THEN
    ASM_REWRITE_TAC[IN_UNIV] THEN ASM_MESON_TAC[]]);;


let CONVERGENT_EQ_CAUCHY = 
prove
 (`!s. (?l. (s --> l) sequentially) <=> cauchy s`,

  GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[LEFT_IMP_EXISTS_THM; CONVERGENT_IMP_CAUCHY];
    REWRITE_TAC[REWRITE_RULE[complete; IN_UNIV] COMPLETE_UNIV]]);;


let CONVERGENT_IMP_BOUNDED = 
prove
 (`!s l. (s --> l) sequentially ==> bounded (IMAGE s (:num))`,

  REWRITE_TAC[LEFT_FORALL_IMP_THM; CONVERGENT_EQ_CAUCHY] THEN
  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP CAUCHY_IMP_BOUNDED) THEN
  REWRITE_TAC[IMAGE; IN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Total boundedness.                                                        *)
(* ------------------------------------------------------------------------- *)


let COMPACT_IMP_TOTALLY_BOUNDED = 
prove
 (`!s:real^N->bool.
        compact s
        ==> !e. &0 < e ==> ?k. FINITE k /\ k SUBSET s /\
                               s SUBSET (UNIONS(IMAGE (\x. ball(x,e)) k))`,

  GEN_TAC THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM] THEN
  REWRITE_TAC[TAUT `~(a /\ b /\ c) <=> a /\ b ==> ~c`; SUBSET] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN
   `?x:num->real^N. !n. x(n) IN s /\ !m. m < n ==> ~(dist(x(m),x(n)) < e)`
  MP_TAC THENL
   [SUBGOAL_THEN
     `?x:num->real^N.
          !n. x(n) = @y. y IN s /\ !m. m < n ==> ~(dist(x(m),y) < e)`
    MP_TAC THENL
     [MATCH_MP_TAC(MATCH_MP WF_REC WF_num) THEN SIMP_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `x:num->real^N` THEN
    DISCH_TAC THEN MATCH_MP_TAC num_WF THEN X_GEN_TAC `n:num` THEN
    FIRST_X_ASSUM(SUBST1_TAC o SPEC `n:num`) THEN STRIP_TAC THEN
    CONV_TAC SELECT_CONV THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `IMAGE (x:num->real^N) {m | m < n}`) THEN
    SIMP_TAC[FINITE_IMAGE; FINITE_NUMSEG_LT; NOT_FORALL_THM; NOT_IMP] THEN
    REWRITE_TAC[IN_UNIONS; IN_IMAGE; IN_ELIM_THM] THEN ASM_MESON_TAC[IN_BALL];
    ALL_TAC] THEN
  REWRITE_TAC[compact; NOT_FORALL_THM] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `x:num->real^N` THEN  REWRITE_TAC[NOT_IMP; FORALL_AND_THM] THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[NOT_EXISTS_THM] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP CONVERGENT_IMP_CAUCHY) THEN
  REWRITE_TAC[cauchy] THEN DISCH_THEN(MP_TAC o SPEC `e:real`) THEN
  ASM_REWRITE_TAC[o_THM; NOT_EXISTS_THM; NOT_IMP; NOT_FORALL_THM; NOT_IMP] THEN
  X_GEN_TAC `N:num` THEN MAP_EVERY EXISTS_TAC [`N:num`; `SUC N`] THEN
  CONJ_TAC THENL [ARITH_TAC; ASM_MESON_TAC[LT]]);;

(* ------------------------------------------------------------------------- *)
(* Heine-Borel theorem (following Burkill & Burkill vol. 2)                  *)
(* ------------------------------------------------------------------------- *)


let HEINE_BOREL_LEMMA = 
prove
 (`!s:real^N->bool.
      compact s
      ==> !t. s SUBSET (UNIONS t) /\ (!b. b IN t ==> open b)
              ==> ?e. &0 < e /\
                      !x. x IN s ==> ?b. b IN t /\ ball(x,e) SUBSET b`,

  GEN_TAC THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM] THEN
  DISCH_THEN(CHOOSE_THEN (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  DISCH_THEN(MP_TAC o GEN `n:num` o SPEC `&1 / (&n + &1)`) THEN
  SIMP_TAC[REAL_LT_DIV; REAL_LT_01; REAL_ARITH `x <= y ==> x < y + &1`;
   FORALL_AND_THM; REAL_POS; NOT_FORALL_THM; NOT_IMP; SKOLEM_THM; compact] THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN REWRITE_TAC[NOT_EXISTS_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN ASM_REWRITE_TAC[] THEN
  DISCH_TAC THEN MAP_EVERY X_GEN_TAC [`l:real^N`; `r:num->num`] THEN
  STRIP_TAC THEN
  SUBGOAL_THEN `?b:real^N->bool. l IN b /\ b IN t` STRIP_ASSUME_TAC THENL
   [ASM_MESON_TAC[SUBSET; IN_UNIONS]; ALL_TAC] THEN
  SUBGOAL_THEN `?e. &0 < e /\ !z:real^N. dist(z,l) < e ==> z IN b`
  STRIP_ASSUME_TAC THENL [ASM_MESON_TAC[open_def]; ALL_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIM_SEQUENTIALLY]) THEN
  DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN
  SUBGOAL_THEN `&0 < e / &2` (fun th ->
    REWRITE_TAC[th; o_THM] THEN MP_TAC(GEN_REWRITE_RULE I [REAL_ARCH_INV] th))
  THENL [ASM_REWRITE_TAC[REAL_HALF]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `N1:num` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `N2:num` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPECL
   [`(r:num->num)(N1 + N2)`; `b:real^N->bool`]) THEN
  ASM_REWRITE_TAC[SUBSET] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN MATCH_MP_TAC DIST_TRIANGLE_HALF_R THEN
  EXISTS_TAC `(f:num->real^N)(r(N1 + N2:num))` THEN CONJ_TAC THENL
   [ALL_TAC; FIRST_X_ASSUM MATCH_MP_TAC THEN ARITH_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [IN_BALL]) THEN
  MATCH_MP_TAC(REAL_ARITH `a <= b ==> x < a ==> x < b`) THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `inv(&N1)` THEN
  ASM_SIMP_TAC[REAL_LT_IMP_LE] THEN REWRITE_TAC[real_div; REAL_MUL_LID] THEN
  MATCH_MP_TAC REAL_LE_INV2 THEN
  REWRITE_TAC[REAL_OF_NUM_ADD; REAL_OF_NUM_LE; REAL_OF_NUM_LT] THEN
  ASM_MESON_TAC[ARITH_RULE `(~(n = 0) ==> 0 < n)`; LE_ADD; MONOTONE_BIGGER;
                LT_IMP_LE; LE_TRANS]);;


let COMPACT_IMP_HEINE_BOREL = 
prove
 (`!s. compact (s:real^N->bool)
       ==> !f. (!t. t IN f ==> open t) /\ s SUBSET (UNIONS f)
               ==> ?f'. f' SUBSET f /\ FINITE f' /\ s SUBSET (UNIONS f')`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `f:(real^N->bool)->bool` o
    MATCH_MP HEINE_BOREL_LEMMA) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; SUBSET; IN_BALL] THEN
  DISCH_THEN(X_CHOOSE_TAC `B:real^N->real^N->bool`) THEN
  FIRST_ASSUM(MP_TAC o SPEC `e:real` o
    MATCH_MP COMPACT_IMP_TOTALLY_BOUNDED) THEN
  ASM_REWRITE_TAC[UNIONS_IMAGE; SUBSET; IN_ELIM_THM] THEN
  REWRITE_TAC[IN_UNIONS; IN_BALL] THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real^N->bool` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `IMAGE (B:real^N->real^N->bool) k` THEN
  ASM_SIMP_TAC[FINITE_IMAGE; SUBSET; IN_IMAGE; LEFT_IMP_EXISTS_THM] THEN
  ASM_MESON_TAC[IN_BALL]);;

(* ------------------------------------------------------------------------- *)
(* Bolzano-Weierstrass property.                                             *)
(* ------------------------------------------------------------------------- *)


let HEINE_BOREL_IMP_BOLZANO_WEIERSTRASS = 
prove
 (`!s:real^N->bool.
        (!f. (!t. t IN f ==> open t) /\ s SUBSET (UNIONS f)
             ==> ?f'. f' SUBSET f /\ FINITE f' /\ s SUBSET (UNIONS f'))
        ==> !t. INFINITE t /\ t SUBSET s ==> ?x. x IN s /\ x limit_point_of t`,

  REWRITE_TAC[RIGHT_IMP_FORALL_THM; limit_point_of] THEN REPEAT GEN_TAC THEN
  ONCE_REWRITE_TAC[TAUT `a ==> b /\ c ==> d <=> c ==> ~d ==> a ==> ~b`] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_EXISTS_THM; RIGHT_AND_FORALL_THM] THEN
  DISCH_TAC THEN REWRITE_TAC[SKOLEM_THM] THEN
  DISCH_THEN(X_CHOOSE_TAC `f:real^N->real^N->bool`) THEN
  DISCH_THEN(MP_TAC o SPEC
   `{t:real^N->bool | ?x:real^N. x IN s /\ (t = f x)}`) THEN
  REWRITE_TAC[INFINITE; SUBSET; IN_ELIM_THM; IN_UNIONS; NOT_IMP] THEN
  ANTS_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `g:(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC FINITE_SUBSET THEN
  EXISTS_TAC `{x:real^N | x IN t /\ (f(x):real^N->bool) IN g}` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC FINITE_IMAGE_INJ_GENERAL THEN ASM_MESON_TAC[SUBSET];
    SIMP_TAC[SUBSET; IN_ELIM_THM] THEN X_GEN_TAC `u:real^N` THEN
    DISCH_TAC THEN SUBGOAL_THEN `(u:real^N) IN s` ASSUME_TAC THEN
    ASM_MESON_TAC[SUBSET]]);;

(* ------------------------------------------------------------------------- *)
(* Complete the chain of compactness variants.                               *)
(* ------------------------------------------------------------------------- *)


let BOLZANO_WEIERSTRASS_IMP_BOUNDED = 
prove
 (`!s:real^N->bool.
        (!t. INFINITE t /\ t SUBSET s ==> ?x. x limit_point_of t)
        ==> bounded s`,

  GEN_TAC THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  SIMP_TAC[compact; bounded] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_EXISTS_THM; SKOLEM_THM; NOT_IMP] THEN
  REWRITE_TAC[REAL_NOT_LE] THEN
  DISCH_THEN(X_CHOOSE_TAC `beyond:real->real^N`) THEN
  (MP_TAC o prove_recursive_functions_exist num_RECURSION)
   `(f(0) = beyond(&0)) /\
    (!n. f(SUC n) = beyond(norm(f n) + &1):real^N)` THEN
  DISCH_THEN(X_CHOOSE_THEN `x:num->real^N` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `IMAGE (x:num->real^N) UNIV` THEN
  SUBGOAL_THEN
   `!m n. m < n ==> norm((x:num->real^N) m) + &1 < norm(x n)`
  ASSUME_TAC THENL
   [GEN_TAC THEN INDUCT_TAC THEN ASM_REWRITE_TAC[LT] THEN
    ASM_MESON_TAC[REAL_LT_TRANS; REAL_ARITH `b < b + &1`];
    ALL_TAC] THEN
  SUBGOAL_THEN `!m n. ~(m = n) ==> &1 < dist((x:num->real^N) m,x n)`
  ASSUME_TAC THENL
   [REPEAT GEN_TAC THEN REPEAT_TCL DISJ_CASES_THEN ASSUME_TAC
     (SPECL [`m:num`; `n:num`] LT_CASES) THEN
    ASM_MESON_TAC[dist; LT_CASES; NORM_TRIANGLE_SUB; NORM_SUB;
                  REAL_ARITH `x + &1 < y /\ y <= x + d ==> &1 < d`];
    ALL_TAC] THEN
  REPEAT CONJ_TAC THENL
   [ASM_MESON_TAC[INFINITE_IMAGE_INJ; num_INFINITE; DIST_REFL;
                  REAL_ARITH `~(&1 < &0)`];
    REWRITE_TAC[SUBSET; IN_IMAGE; IN_UNIV; LEFT_IMP_EXISTS_THM] THEN
    GEN_TAC THEN INDUCT_TAC THEN ASM_MESON_TAC[];
    ALL_TAC] THEN
  X_GEN_TAC `l:real^N` THEN REWRITE_TAC[LIMPT_APPROACHABLE] THEN
  REWRITE_TAC[IN_IMAGE; IN_UNIV; LEFT_AND_EXISTS_THM] THEN
  ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN REWRITE_TAC[UNWIND_THM2] THEN
  STRIP_TAC THEN FIRST_ASSUM(MP_TAC o SPEC `&1 / &2`) THEN
  CONV_TAC REAL_RAT_REDUCE_CONV THEN
  DISCH_THEN(X_CHOOSE_THEN `k:num` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `dist((x:num->real^N) k,l)`) THEN
  ASM_SIMP_TAC[DIST_POS_LT] THEN
  DISCH_THEN(X_CHOOSE_THEN `m:num` STRIP_ASSUME_TAC) THEN
  ASM_CASES_TAC `m:num = k` THEN
  ASM_MESON_TAC[DIST_TRIANGLE_HALF_L; REAL_LT_TRANS; REAL_LT_REFL]);;


let SEQUENCE_INFINITE_LEMMA = 
prove
 (`!f l. (!n. ~(f(n) = l)) /\ (f --> l) sequentially
         ==> INFINITE {y:real^N | ?n. y = f n}`,

  REWRITE_TAC[INFINITE] THEN REPEAT STRIP_TAC THEN MP_TAC(ISPEC
   `IMAGE (\y:real^N. dist(y,l)) {y | ?n:num. y = f n}` INF_FINITE) THEN
  ASM_SIMP_TAC[GSYM MEMBER_NOT_EMPTY; IN_IMAGE; FINITE_IMAGE; IN_ELIM_THM] THEN
  ASM_MESON_TAC[LIM_SEQUENTIALLY; LE_REFL; REAL_NOT_LE; DIST_POS_LT]);;


let LIMPT_OF_SEQUENCE_SUBSEQUENCE = 
prove
 (`!f:num->real^N l.
        l limit_point_of (IMAGE f (:num))
        ==> ?r. (!m n. m < n ==> r(m) < r(n)) /\ ((f o r) --> l) sequentially`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIMPT_APPROACHABLE]) THEN
  DISCH_THEN(MP_TAC o GEN `n:num` o SPEC
   `inf((inv(&n + &1)) INSERT
    IMAGE (\k. dist((f:num->real^N) k,l))
          {k | k IN 0..n /\ ~(f k = l)})`) THEN
  SIMP_TAC[REAL_LT_INF_FINITE; FINITE_INSERT; NOT_INSERT_EMPTY;
           FINITE_RESTRICT; FINITE_NUMSEG; FINITE_IMAGE] THEN
  REWRITE_TAC[FORALL_IN_INSERT; EXISTS_IN_IMAGE; FORALL_IN_IMAGE; IN_UNIV] THEN
  REWRITE_TAC[REAL_LT_INV_EQ; REAL_ARITH `&0 < &n + &1`] THEN
  SIMP_TAC[FORALL_AND_THM; FORALL_IN_GSPEC; GSYM DIST_NZ; SKOLEM_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `nn:num->num` STRIP_ASSUME_TAC) THEN
  (MP_TAC o prove_recursive_functions_exist num_RECURSION)
   `r 0 = nn 0 /\ (!n. r (SUC n) = nn(r n))` THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `r:num->num` THEN
  STRIP_TAC THEN
  MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
   [MATCH_MP_TAC TRANSITIVE_STEPWISE_LT THEN REWRITE_TAC[LT_TRANS] THEN
    X_GEN_TAC `n:num` THEN ASM_REWRITE_TAC[] THEN
    FIRST_X_ASSUM(MP_TAC o SPECL
     [`(r:num->num) n`; `(nn:num->num)(r(n:num))`]) THEN
    ASM_REWRITE_TAC[IN_NUMSEG; LE_0; REAL_LT_REFL] THEN ARITH_TAC;
    DISCH_THEN(ASSUME_TAC o MATCH_MP MONOTONE_BIGGER)] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  X_GEN_TAC `e:real` THEN GEN_REWRITE_TAC LAND_CONV [REAL_ARCH_INV] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN STRIP_TAC THEN
  MATCH_MP_TAC num_INDUCTION THEN ASM_REWRITE_TAC[CONJUNCT1 LE] THEN
  X_GEN_TAC `n:num` THEN DISCH_THEN(K ALL_TAC) THEN DISCH_TAC THEN
  ASM_REWRITE_TAC[o_THM] THEN MATCH_MP_TAC REAL_LT_TRANS THEN
  EXISTS_TAC `inv(&((r:num->num) n) + &1)` THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC `inv(&N)` THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_LE_INV2 THEN
  ASM_SIMP_TAC[REAL_OF_NUM_LE; REAL_OF_NUM_LT; LE_1; REAL_OF_NUM_ADD] THEN
  MATCH_MP_TAC(ARITH_RULE `N <= SUC n /\ n <= r n ==> N <= r n + 1`) THEN
  ASM_REWRITE_TAC[]);;


let SEQUENCE_UNIQUE_LIMPT = 
prove
 (`!f l l':real^N.
        (f --> l) sequentially /\ l' limit_point_of {y | ?n. y = f n}
        ==> l' = l`,

  REWRITE_TAC[SET_RULE `{y | ?n. y = f n} = IMAGE f (:num)`] THEN
  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP LIMPT_OF_SEQUENCE_SUBSEQUENCE) THEN
  DISCH_THEN(X_CHOOSE_THEN `r:num->num` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_UNIQUE) THEN
  EXISTS_TAC `(f:num->real^N) o (r:num->num)` THEN
  ASM_SIMP_TAC[TRIVIAL_LIMIT_SEQUENTIALLY; LIM_SUBSEQUENCE]);;


let BOLZANO_WEIERSTRASS_IMP_CLOSED = 
prove
 (`!s:real^N->bool.
        (!t. INFINITE t /\ t SUBSET s ==> ?x. x IN s /\ x limit_point_of t)
        ==> closed s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CLOSED_SEQUENTIAL_LIMITS] THEN
  MAP_EVERY X_GEN_TAC [`f:num->real^N`; `l:real^N`] THEN
  DISCH_TAC THEN
  MAP_EVERY (MP_TAC o ISPECL [`f:num->real^N`; `l:real^N`])
   [SEQUENCE_UNIQUE_LIMPT; SEQUENCE_INFINITE_LEMMA] THEN
  MATCH_MP_TAC(TAUT
   `(~d ==> a /\ ~(b /\ c)) ==> (a ==> b) ==> c ==> d`) THEN
  DISCH_TAC THEN CONJ_TAC THENL [ASM_MESON_TAC[]; STRIP_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `{y:real^N | ?n:num. y = f n}`) THEN
  ASM_REWRITE_TAC[NOT_IMP] THEN CONJ_TAC THENL
   [REWRITE_TAC[SUBSET; IN_ELIM_THM];
    ABBREV_TAC `t = {y:real^N | ?n:num. y = f n}`] THEN
  ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Hence express everything as an equivalence.                               *)
(* ------------------------------------------------------------------------- *)


let COMPACT_EQ_HEINE_BOREL = 
prove
 (`!s:real^N->bool.
        compact s <=>
           !f. (!t. t IN f ==> open t) /\ s SUBSET (UNIONS f)
               ==> ?f'. f' SUBSET f /\ FINITE f' /\ s SUBSET (UNIONS f')`,

  GEN_TAC THEN EQ_TAC THEN SIMP_TAC[COMPACT_IMP_HEINE_BOREL] THEN
  DISCH_THEN(MP_TAC o MATCH_MP HEINE_BOREL_IMP_BOLZANO_WEIERSTRASS) THEN
  DISCH_TAC THEN MATCH_MP_TAC BOUNDED_CLOSED_IMP_COMPACT THEN
  ASM_MESON_TAC[BOLZANO_WEIERSTRASS_IMP_BOUNDED;
                BOLZANO_WEIERSTRASS_IMP_CLOSED]);;


let COMPACT_EQ_BOLZANO_WEIERSTRASS = 
prove
 (`!s:real^N->bool.
        compact s <=>
           !t. INFINITE t /\ t SUBSET s ==> ?x. x IN s /\ x limit_point_of t`,


let COMPACT_EQ_BOUNDED_CLOSED = 
prove
 (`!s:real^N->bool. compact s <=> bounded s /\ closed s`,


let COMPACT_IMP_BOUNDED = 
prove
 (`!s. compact s ==> bounded s`,


let COMPACT_IMP_CLOSED = 
prove
 (`!s. compact s ==> closed s`,


let COMPACT_SEQUENCE_WITH_LIMIT = 
prove
 (`!f l:real^N.
        (f --> l) sequentially ==> compact (l INSERT IMAGE f (:num))`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN
  REWRITE_TAC[BOUNDED_INSERT] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[CONVERGENT_IMP_BOUNDED];
    SIMP_TAC[CLOSED_LIMPT; LIMPT_INSERT; IN_INSERT] THEN
    REWRITE_TAC[IMAGE; IN_UNIV] THEN REPEAT STRIP_TAC THEN DISJ1_TAC THEN
    MATCH_MP_TAC SEQUENCE_UNIQUE_LIMPT THEN ASM_MESON_TAC[]]);;


let CLOSED_IN_COMPACT = 
prove
 (`!s t:real^N->bool.
        compact s /\ closed_in (subtopology euclidean s) t
        ==> compact t`,


let CLOSED_IN_COMPACT_EQ = 
prove
 (`!s t. compact s
         ==> (closed_in (subtopology euclidean s) t <=>
              compact t /\ t SUBSET s)`,

(* ------------------------------------------------------------------------- *)
(* A version of Heine-Borel for subtopology.                                 *)
(* ------------------------------------------------------------------------- *)


let COMPACT_EQ_HEINE_BOREL_SUBTOPOLOGY = 
prove
 (`!s:real^N->bool.
        compact s <=>
        (!f. (!t. t IN f ==> open_in(subtopology euclidean s) t) /\
             s SUBSET UNIONS f
             ==> ?f'. f' SUBSET f /\ FINITE f' /\ s SUBSET UNIONS f')`,

  GEN_TAC THEN REWRITE_TAC[COMPACT_EQ_HEINE_BOREL] THEN EQ_TAC THEN
  DISCH_TAC THEN X_GEN_TAC `f:(real^N->bool)->bool` THENL
   [REWRITE_TAC[OPEN_IN_OPEN] THEN
    GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[SKOLEM_THM] THEN
    DISCH_THEN(CONJUNCTS_THEN2
     (X_CHOOSE_TAC `m:(real^N->bool)->(real^N->bool)`) ASSUME_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC
     `IMAGE (m:(real^N->bool)->(real^N->bool)) f`) THEN
    ASM_SIMP_TAC[FORALL_IN_IMAGE] THEN
    ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    DISCH_THEN(X_CHOOSE_THEN `f':(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `IMAGE (\t:real^N->bool. s INTER t) f'` THEN
    ASM_SIMP_TAC[FINITE_IMAGE; UNIONS_IMAGE; SUBSET; FORALL_IN_IMAGE] THEN
    CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [SUBSET_IMAGE]) THEN
    STRIP_TAC THEN ASM_REWRITE_TAC[FORALL_IN_IMAGE] THEN ASM_MESON_TAC[SUBSET];
    DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `{s INTER t:real^N->bool | t IN f}`) THEN
    REWRITE_TAC[SIMPLE_IMAGE; FORALL_IN_IMAGE; OPEN_IN_OPEN; UNIONS_IMAGE] THEN
    ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    ONCE_REWRITE_TAC[TAUT `a /\ b /\ c <=> b /\ a /\ c`] THEN
    REWRITE_TAC[EXISTS_FINITE_SUBSET_IMAGE; UNIONS_IMAGE] THEN
    MATCH_MP_TAC MONO_EXISTS THEN SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* More easy lemmas.                                                         *)
(* ------------------------------------------------------------------------- *)


let COMPACT_CLOSURE = 
prove
 (`!s. compact(closure s) <=> bounded s`,


let BOLZANO_WEIERSTRASS_CONTRAPOS = 
prove
 (`!s t:real^N->bool.
        compact s /\ t SUBSET s /\
        (!x. x IN s ==> ~(x limit_point_of t))
        ==> FINITE t`,

  REWRITE_TAC[COMPACT_EQ_BOLZANO_WEIERSTRASS; INFINITE] THEN MESON_TAC[]);;


let DISCRETE_BOUNDED_IMP_FINITE = 
prove
 (`!s:real^N->bool e.
        &0 < e /\
        (!x y. x IN s /\ y IN s /\ norm(y - x) < e ==> y = x) /\
        bounded s
        ==> FINITE s`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `compact(s:real^N->bool)` MP_TAC THENL
   [ASM_REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN
    ASM_MESON_TAC[DISCRETE_IMP_CLOSED];
    DISCH_THEN(MP_TAC o MATCH_MP COMPACT_IMP_HEINE_BOREL)] THEN
  DISCH_THEN(MP_TAC o SPEC `IMAGE (\x:real^N. ball(x,e)) s`) THEN
  REWRITE_TAC[FORALL_IN_IMAGE; OPEN_BALL; UNIONS_IMAGE; IN_ELIM_THM] THEN
  ANTS_TAC THENL
   [REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN ASM_MESON_TAC[CENTRE_IN_BALL];
    ONCE_REWRITE_TAC[TAUT `a /\ b /\ c <=> b /\ a /\ c`]] THEN
  REWRITE_TAC[EXISTS_FINITE_SUBSET_IMAGE] THEN
  DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `s:real^N->bool = t` (fun th -> ASM_REWRITE_TAC[th]) THEN
  MATCH_MP_TAC SUBSET_ANTISYM THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[SUBSET] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [UNIONS_IMAGE]) THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^N` o GEN_REWRITE_RULE I [SUBSET]) THEN
  ASM_REWRITE_TAC[IN_ELIM_THM; IN_BALL; dist] THEN ASM_MESON_TAC[SUBSET]);;


let BOLZANO_WEIERSTRASS = 
prove
 (`!s:real^N->bool. bounded s /\ INFINITE s ==> ?x. x limit_point_of s`,

  GEN_TAC THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP NO_LIMIT_POINT_IMP_CLOSED) THEN
  STRIP_TAC THEN
  MP_TAC(ISPEC `s:real^N->bool` COMPACT_EQ_BOLZANO_WEIERSTRASS) THEN
  ASM_REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN
  DISCH_THEN(MP_TAC o SPEC `s:real^N->bool`) THEN
  ASM_REWRITE_TAC[SUBSET_REFL] THEN ASM_MESON_TAC[]);;


let BOUNDED_EQ_BOLZANO_WEIERSTRASS = 
prove
 (`!s:real^N->bool.
        bounded s <=> !t. t SUBSET s /\ INFINITE t ==> ?x. x limit_point_of t`,

(* ------------------------------------------------------------------------- *)
(* In particular, some common special cases.                                 *)
(* ------------------------------------------------------------------------- *)


let COMPACT_EMPTY = 
prove
 (`compact {}`,

  REWRITE_TAC[compact; NOT_IN_EMPTY]);;


let COMPACT_UNION = 
prove
 (`!s t. compact s /\ compact t ==> compact (s UNION t)`,


let COMPACT_INTER = 
prove
 (`!s t. compact s /\ compact t ==> compact (s INTER t)`,


let COMPACT_INTER_CLOSED = 
prove
 (`!s t. compact s /\ closed t ==> compact (s INTER t)`,


let CLOSED_INTER_COMPACT = 
prove
 (`!s t. closed s /\ compact t ==> compact (s INTER t)`,


let COMPACT_INTERS = 
prove
 (`!f:(real^N->bool)->bool.
        (!s. s IN f ==> compact s) /\ ~(f = {})
        ==> compact(INTERS f)`,

  SIMP_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_INTERS] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC BOUNDED_INTERS THEN ASM SET_TAC[]);;


let FINITE_IMP_CLOSED = 
prove
 (`!s. FINITE s ==> closed s`,


let FINITE_IMP_CLOSED_IN = 
prove
 (`!s t. FINITE s /\ s SUBSET t ==> closed_in (subtopology euclidean t) s`,


let FINITE_IMP_COMPACT = 
prove
 (`!s. FINITE s ==> compact s`,


let COMPACT_SING = 
prove
 (`!a. compact {a}`,


let COMPACT_INSERT = 
prove
 (`!a s. compact s ==> compact(a INSERT s)`,

  ONCE_REWRITE_TAC[SET_RULE `a INSERT s = {a} UNION s`] THEN
  SIMP_TAC[COMPACT_UNION; COMPACT_SING]);;


let CLOSED_SING = 
prove
 (`!a. closed {a}`,


let CLOSED_IN_SING = 
prove
 (`!u x:real^N. closed_in (subtopology euclidean u) {x} <=> x IN u`,

  SIMP_TAC[CLOSED_SUBSET_EQ; CLOSED_SING] THEN SET_TAC[]);;


let CLOSURE_SING = 
prove
 (`!x:real^N. closure {x} = {x}`,


let CLOSED_INSERT = 
prove
 (`!a s. closed s ==> closed(a INSERT s)`,

  ONCE_REWRITE_TAC[SET_RULE `a INSERT s = {a} UNION s`] THEN
  SIMP_TAC[CLOSED_UNION; CLOSED_SING]);;


let COMPACT_CBALL = 
prove
 (`!x e. compact(cball(x,e))`,


let COMPACT_FRONTIER_BOUNDED = 
prove
 (`!s. bounded s ==> compact(frontier s)`,


let COMPACT_FRONTIER = 
prove
 (`!s. compact s ==> compact (frontier s)`,


let BOUNDED_FRONTIER = 
prove
 (`!s:real^N->bool. bounded s ==> bounded(frontier s)`,


let FRONTIER_SUBSET_COMPACT = 
prove
 (`!s. compact s ==> frontier s SUBSET s`,


let OPEN_DELETE = 
prove
 (`!s x. open s ==> open(s DELETE x)`,

  
let lemma = prove(`s DELETE x = s DIFF {x}`,SET_TAC[]) in
  SIMP_TAC[lemma; OPEN_DIFF; CLOSED_SING]);;


let OPEN_IN_DELETE = 
prove
 (`!u s a:real^N.
        open_in (subtopology euclidean u) s
        ==> open_in (subtopology euclidean u) (s DELETE a)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `(a:real^N) IN s` THENL
   [ONCE_REWRITE_TAC[SET_RULE `s DELETE a = s DIFF {a}`] THEN
    MATCH_MP_TAC OPEN_IN_DIFF THEN ASM_REWRITE_TAC[CLOSED_IN_SING] THEN
    FIRST_X_ASSUM(MP_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN ASM SET_TAC[];
    ASM_SIMP_TAC[SET_RULE `~(a IN s) ==> s DELETE a = s`]]);;


let CLOSED_INTERS_COMPACT = 
prove
 (`!s:real^N->bool.
        closed s <=> !e. compact(cball(vec 0,e) INTER s)`,

  GEN_TAC THEN EQ_TAC THENL
   [SIMP_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_INTER; CLOSED_CBALL;
             BOUNDED_INTER; BOUNDED_CBALL];
    ALL_TAC] THEN
  STRIP_TAC THEN REWRITE_TAC[CLOSED_LIMPT] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `norm(x:real^N) + &1`) THEN
  DISCH_THEN(MP_TAC o MATCH_MP COMPACT_IMP_CLOSED) THEN
  REWRITE_TAC[CLOSED_LIMPT] THEN DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
  REWRITE_TAC[IN_INTER] THEN ANTS_TAC THENL [ALL_TAC; MESON_TAC[]] THEN
  POP_ASSUM MP_TAC THEN REWRITE_TAC[LIMPT_APPROACHABLE] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `min e (&1 / &2)`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; MATCH_MP_TAC MONO_EXISTS] THEN
  X_GEN_TAC `y:real^N` THEN SIMP_TAC[IN_INTER; IN_CBALL] THEN NORM_ARITH_TAC);;


let COMPACT_UNIONS = 
prove
 (`!s. FINITE s /\ (!t. t IN s ==> compact t) ==> compact(UNIONS s)`,


let COMPACT_DIFF = 
prove
 (`!s t. compact s /\ open t ==> compact(s DIFF t)`,

  ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s INTER (UNIV DIFF t)`] THEN
  SIMP_TAC[COMPACT_INTER_CLOSED; GSYM OPEN_CLOSED]);;


let COMPACT_SPHERE = 
prove
 (`!a:real^N r. compact(sphere(a,r))`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[GSYM FRONTIER_CBALL] THEN MATCH_MP_TAC COMPACT_FRONTIER THEN
  REWRITE_TAC[COMPACT_CBALL]);;


let BOUNDED_SPHERE = 
prove
 (`!a:real^N r. bounded(sphere(a,r))`,


let CLOSED_SPHERE = 
prove
 (`!a r. closed(sphere(a,r))`,


let FRONTIER_SING = 
prove
 (`!a:real^N. frontier {a} = {a}`,

  REWRITE_TAC[frontier; CLOSURE_SING; INTERIOR_SING; DIFF_EMPTY]);;

(* ------------------------------------------------------------------------- *)
(* Finite intersection property. I could make it an equivalence in fact.     *)
(* ------------------------------------------------------------------------- *)


let COMPACT_IMP_FIP = 
prove
 (`!s:real^N->bool f.
        compact s /\
        (!t. t IN f ==> closed t) /\
        (!f'. FINITE f' /\ f' SUBSET f ==> ~(s INTER (INTERS f') = {}))
        ==> ~(s INTER (INTERS f) = {})`,

  
let lemma = prove(`(s = UNIV DIFF t) <=> (UNIV DIFF s = t)`,SET_TAC[]) in
  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [COMPACT_EQ_HEINE_BOREL]) THEN
  DISCH_THEN(MP_TAC o SPEC `IMAGE (\t:real^N->bool. UNIV DIFF t) f`) THEN
  ASM_SIMP_TAC[FORALL_IN_IMAGE] THEN
  DISCH_THEN(fun th -> REPEAT STRIP_TAC THEN MP_TAC th) THEN
  ASM_SIMP_TAC[OPEN_DIFF; CLOSED_DIFF; OPEN_UNIV; CLOSED_UNIV; NOT_IMP] THEN
  CONJ_TAC THENL
   [UNDISCH_TAC `(s:real^N->bool) INTER INTERS f = {}` THEN
    ONCE_REWRITE_TAC[SUBSET; EXTENSION] THEN
    REWRITE_TAC[IN_UNIONS; EXISTS_IN_IMAGE] THEN SET_TAC[];
    DISCH_THEN(X_CHOOSE_THEN `g:(real^N->bool)->bool` MP_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `IMAGE (\t:real^N->bool. UNIV DIFF t) g`) THEN
    ASM_CASES_TAC `FINITE(g:(real^N->bool)->bool)` THEN
    ASM_SIMP_TAC[FINITE_IMAGE] THEN ONCE_REWRITE_TAC[SUBSET; EXTENSION] THEN
    REWRITE_TAC[FORALL_IN_IMAGE; IN_INTER; IN_INTERS; IN_IMAGE; IN_DIFF;
                IN_UNIV; NOT_IN_EMPTY; lemma; UNWIND_THM1; IN_UNIONS] THEN
    SET_TAC[]]);;


let CLOSED_IMP_FIP = 
prove
 (`!s:real^N->bool f.
        closed s /\
        (!t. t IN f ==> closed t) /\ (?t. t IN f /\ bounded t) /\
        (!f'. FINITE f' /\ f' SUBSET f ==> ~(s INTER (INTERS f') = {}))
        ==> ~(s INTER (INTERS f) = {})`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN MATCH_MP_TAC(SET_RULE
   `~((s INTER t) INTER u = {}) ==> ~(s INTER u = {})`) THEN
  MATCH_MP_TAC COMPACT_IMP_FIP THEN ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[CLOSED_INTER_COMPACT; COMPACT_EQ_BOUNDED_CLOSED];
    REWRITE_TAC[INTER_ASSOC] THEN ONCE_REWRITE_TAC[GSYM INTERS_INSERT]] THEN
  GEN_TAC THEN STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[FINITE_INSERT; INSERT_SUBSET]);;


let CLOSED_IMP_FIP_COMPACT = 
prove
 (`!s:real^N->bool f.
        closed s /\ (!t. t IN f ==> compact t) /\
        (!f'. FINITE f' /\ f' SUBSET f ==> ~(s INTER (INTERS f') = {}))
        ==> ~(s INTER (INTERS f) = {})`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `f:(real^N->bool)->bool = {}` THEN
  ASM_SIMP_TAC[SUBSET_EMPTY; INTERS_0; INTER_UNIV] THENL
   [MESON_TAC[FINITE_EMPTY]; ALL_TAC] THEN
  STRIP_TAC THEN MATCH_MP_TAC CLOSED_IMP_FIP THEN
  ASM_MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; MEMBER_NOT_EMPTY]);;


let CLOSED_FIP = 
prove
 (`!f. (!t:real^N->bool. t IN f ==> closed t) /\ (?t. t IN f /\ bounded t) /\
       (!f'. FINITE f' /\ f' SUBSET f ==> ~(INTERS f' = {}))
       ==> ~(INTERS f = {})`,

  GEN_TAC THEN DISCH_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `s = {} <=> UNIV INTER s = {}`] THEN
  MATCH_MP_TAC CLOSED_IMP_FIP THEN ASM_REWRITE_TAC[CLOSED_UNIV; INTER_UNIV]);;


let COMPACT_FIP = 
prove
 (`!f. (!t:real^N->bool. t IN f ==> compact t) /\
       (!f'. FINITE f' /\ f' SUBSET f ==> ~(INTERS f' = {}))
       ==> ~(INTERS f = {})`,

  GEN_TAC THEN DISCH_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `s = {} <=> UNIV INTER s = {}`] THEN
  MATCH_MP_TAC CLOSED_IMP_FIP_COMPACT THEN
  ASM_REWRITE_TAC[CLOSED_UNIV; INTER_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Bounded closed nest property (proof does not use Heine-Borel).            *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_CLOSED_NEST = 
prove
 (`!s. (!n. closed(s n)) /\ (!n. ~(s n = {})) /\
       (!m n. m <= n ==> s(n) SUBSET s(m)) /\
       bounded(s 0)
       ==> ?a:real^N. !n:num. a IN s(n)`,

  GEN_TAC THEN REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; SKOLEM_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2
     (X_CHOOSE_TAC `a:num->real^N`) STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `compact(s 0:real^N->bool)` MP_TAC THENL
   [ASM_MESON_TAC[BOUNDED_CLOSED_IMP_COMPACT]; ALL_TAC] THEN
  REWRITE_TAC[compact] THEN
  DISCH_THEN(MP_TAC o SPEC `a:num->real^N`) THEN
  ANTS_TAC THENL [ASM_MESON_TAC[SUBSET; LE_0]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `l:real^N` THEN
  REWRITE_TAC[LIM_SEQUENTIALLY; o_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `r:num->num` STRIP_ASSUME_TAC) THEN
  GEN_REWRITE_TAC I [TAUT `p <=> ~(~p)`] THEN
  GEN_REWRITE_TAC RAND_CONV [NOT_FORALL_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `N:num` MP_TAC) THEN
  MP_TAC(ISPECL [`l:real^N`; `(s:num->real^N->bool) N`]
                CLOSED_APPROACHABLE) THEN
  ASM_MESON_TAC[SUBSET; LE_REFL; LE_TRANS; LE_CASES; MONOTONE_BIGGER]);;

(* ------------------------------------------------------------------------- *)
(* Decreasing case does not even need compactness, just completeness.        *)
(* ------------------------------------------------------------------------- *)


let DECREASING_CLOSED_NEST = 
prove
 (`!s. (!n. closed(s n)) /\ (!n. ~(s n = {})) /\
       (!m n. m <= n ==> s(n) SUBSET s(m)) /\
       (!e. &0 < e ==> ?n. !x y. x IN s(n) /\ y IN s(n) ==> dist(x,y) < e)
       ==> ?a:real^N. !n:num. a IN s(n)`,

  GEN_TAC THEN REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; SKOLEM_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2
     (X_CHOOSE_TAC `a:num->real^N`) STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `?l:real^N. (a --> l) sequentially` MP_TAC THENL
   [ASM_MESON_TAC[cauchy; GE; SUBSET; LE_TRANS; LE_REFL;
                  complete; COMPLETE_UNIV; IN_UNIV];
    ASM_MESON_TAC[LIM_SEQUENTIALLY; CLOSED_APPROACHABLE;
                  SUBSET; LE_REFL; LE_TRANS; LE_CASES]]);;

(* ------------------------------------------------------------------------- *)
(* Strengthen it to the intersection actually being a singleton.             *)
(* ------------------------------------------------------------------------- *)


let DECREASING_CLOSED_NEST_SING = 
prove
 (`!s. (!n. closed(s n)) /\ (!n. ~(s n = {})) /\
       (!m n. m <= n ==> s(n) SUBSET s(m)) /\
       (!e. &0 < e ==> ?n. !x y. x IN s(n) /\ y IN s(n) ==> dist(x,y) < e)
       ==> ?a:real^N. INTERS {t | ?n:num. t = s n} = {a}`,

  GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP DECREASING_CLOSED_NEST) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN
  DISCH_TAC THEN REWRITE_TAC[EXTENSION; IN_INTERS; IN_SING; IN_ELIM_THM] THEN
  ASM_MESON_TAC[DIST_POS_LT; REAL_LT_REFL; SUBSET; LE_CASES]);;

(* ------------------------------------------------------------------------- *)
(* A version for a more general chain, not indexed by N.                     *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_CLOSED_CHAIN = 
prove
 (`!f b:real^N->bool.
        (!s. s IN f ==> closed s /\ ~(s = {})) /\
        (!s t. s IN f /\ t IN f ==> s SUBSET t \/ t SUBSET s) /\
         b IN f /\ bounded b
         ==> ~(INTERS f = {})`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  SUBGOAL_THEN `~(b INTER (INTERS f):real^N->bool = {})` MP_TAC THENL
   [ALL_TAC; SET_TAC[]] THEN
  MATCH_MP_TAC COMPACT_IMP_FIP THEN
  ASM_SIMP_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN
  X_GEN_TAC `u:(real^N->bool)->bool` THEN STRIP_TAC THEN
  SUBGOAL_THEN `?s:real^N->bool. s IN f /\ !t. t IN u ==> s SUBSET t`
  MP_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  UNDISCH_TAC `(u:(real^N->bool)->bool) SUBSET f` THEN
  UNDISCH_TAC `FINITE(u:(real^N->bool)->bool)` THEN
  SPEC_TAC(`u:(real^N->bool)->bool`,`u:(real^N->bool)->bool`) THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MAP_EVERY X_GEN_TAC [`t:real^N->bool`; `u:(real^N->bool)->bool`] THEN
  REWRITE_TAC[INSERT_SUBSET] THEN
  DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC STRIP_ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `s:real^N->bool` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`s:real^N->bool`; `t:real^N->bool`]) THEN
  ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Analogous things directly for compactness.                                *)
(* ------------------------------------------------------------------------- *)


let COMPACT_CHAIN = 
prove
 (`!f:(real^N->bool)->bool.
        (!s. s IN f ==> compact s /\ ~(s = {})) /\
        (!s t. s IN f /\ t IN f ==> s SUBSET t \/ t SUBSET s)
        ==> ~(INTERS f = {})`,

  GEN_TAC THEN REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN STRIP_TAC THEN
  ASM_CASES_TAC `f:(real^N->bool)->bool = {}` THENL
   [ASM_REWRITE_TAC[INTERS_0] THEN SET_TAC[];
    MATCH_MP_TAC BOUNDED_CLOSED_CHAIN THEN ASM SET_TAC[]]);;


let COMPACT_NEST = 
prove
 (`!s. (!n. compact(s n) /\ ~(s n = {})) /\
       (!m n. m <= n ==> s n SUBSET s m)
       ==> ~(INTERS {s n | n IN (:num)} = {})`,

  GEN_TAC THEN STRIP_TAC THEN MATCH_MP_TAC COMPACT_CHAIN THEN
  ASM_SIMP_TAC[FORALL_IN_GSPEC; IN_UNIV; IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN
  MATCH_MP_TAC WLOG_LE THEN ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Cauchy-type criteria for *uniform* convergence.                           *)
(* ------------------------------------------------------------------------- *)


let UNIFORMLY_CONVERGENT_EQ_CAUCHY = 
prove
 (`!P s:num->A->real^N.
         (?l. !e. &0 < e
                  ==> ?N. !n x. N <= n /\ P x ==> dist(s n x,l x) < e) <=>
         (!e. &0 < e
              ==> ?N. !m n x. N <= m /\ N <= n /\ P x
                              ==> dist(s m x,s n x) < e)`,

  REPEAT GEN_TAC THEN EQ_TAC THENL
   [DISCH_THEN(X_CHOOSE_TAC `l:A->real^N`) THEN X_GEN_TAC `e:real` THEN
    DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
    ASM_REWRITE_TAC[REAL_HALF] THEN MESON_TAC[DIST_TRIANGLE_HALF_L];
    ALL_TAC] THEN
  DISCH_TAC THEN
  SUBGOAL_THEN `!x:A. P x ==> cauchy (\n. s n x :real^N)` MP_TAC THENL
   [REWRITE_TAC[cauchy; GE] THEN ASM_MESON_TAC[]; ALL_TAC] THEN
  REWRITE_TAC[GSYM CONVERGENT_EQ_CAUCHY; LIM_SEQUENTIALLY] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `l:A->real^N` THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `N:num` THEN STRIP_TAC THEN
  MAP_EVERY X_GEN_TAC [`n:num`; `x:A`] THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:A`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_TAC `M:num`) THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`n:num`; `N + M:num`; `x:A`]) THEN
  ASM_REWRITE_TAC[LE_ADD] THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `M + N:num`) THEN REWRITE_TAC[LE_ADD] THEN
  ASM_MESON_TAC[DIST_TRIANGLE_HALF_L; DIST_SYM]);;


let UNIFORMLY_CONVERGENT_EQ_CAUCHY_ALT = 
prove
 (`!P s:num->A->real^N.
         (?l. !e. &0 < e
                  ==> ?N. !n x. N <= n /\ P x ==> dist(s n x,l x) < e) <=>
         (!e. &0 < e
              ==> ?N. !m n x. N <= m /\ N <= n /\ m < n /\ P x
                              ==> dist(s m x,s n x) < e)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[UNIFORMLY_CONVERGENT_EQ_CAUCHY] THEN
  EQ_TAC THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e:real`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN DISCH_TAC THEN
  ASM_SIMP_TAC[] THEN MATCH_MP_TAC WLOG_LT THEN
  ASM_SIMP_TAC[DIST_REFL] THEN MESON_TAC[DIST_SYM]);;


let UNIFORMLY_CAUCHY_IMP_UNIFORMLY_CONVERGENT = 
prove
 (`!P (s:num->A->real^N) l.
    (!e. &0 < e
         ==> ?N. !m n x. N <= m /\ N <= n /\ P x ==> dist(s m x,s n x) < e) /\
    (!x. P x ==> !e. &0 < e ==> ?N. !n. N <= n ==> dist(s n x,l x) < e)
    ==> (!e. &0 < e ==> ?N. !n x. N <= n /\ P x ==> dist(s n x,l x) < e)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[GSYM UNIFORMLY_CONVERGENT_EQ_CAUCHY] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (X_CHOOSE_TAC `l':A->real^N`) ASSUME_TAC) THEN
  SUBGOAL_THEN `!x. P x ==> (l:A->real^N) x = l' x` MP_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[]] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC(ISPEC `sequentially` LIM_UNIQUE) THEN
  EXISTS_TAC `\n. (s:num->A->real^N) n x` THEN
  REWRITE_TAC[LIM_SEQUENTIALLY; TRIVIAL_LIMIT_SEQUENTIALLY] THEN
  ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Define continuity over a net to take in restrictions of the set.          *)
(* ------------------------------------------------------------------------- *)

parse_as_infix ("continuous",(12,"right"));;


let continuous = new_definition
  `f continuous net <=> (f --> f(netlimit net)) net`;;


let CONTINUOUS_TRIVIAL_LIMIT = 
prove
 (`!f net. trivial_limit net ==> f continuous net`,

  SIMP_TAC[continuous; LIM]);;


let CONTINUOUS_WITHIN = 
prove
 (`!f x:real^M. f continuous (at x within s) <=> (f --> f(x)) (at x within s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous] THEN
  ASM_CASES_TAC `trivial_limit(at (x:real^M) within s)` THENL
   [ASM_REWRITE_TAC[LIM]; ASM_SIMP_TAC[NETLIMIT_WITHIN]]);;


let CONTINUOUS_AT = 
prove
 (`!f (x:real^N). f continuous (at x) <=> (f --> f(x)) (at x)`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[CONTINUOUS_WITHIN; IN_UNIV]);;


let CONTINUOUS_AT_WITHIN = 
prove
 (`!f:real^M->real^N x s.
        f continuous (at x) ==> f continuous (at x within s)`,


let CONTINUOUS_WITHIN_CLOSED_NONTRIVIAL = 
prove
 (`!a s. closed s /\ ~(a IN s) ==> f continuous (at a within s)`,

  ASM_SIMP_TAC[continuous; LIM; LIM_WITHIN_CLOSED_TRIVIAL]);;


let CONTINUOUS_TRANSFORM_WITHIN = 
prove
 (`!f g:real^M->real^N s x d.
        &0 < d /\ x IN s /\
        (!x'. x' IN s /\ dist(x',x) < d ==> f(x') = g(x')) /\
        f continuous (at x within s)
        ==> g continuous (at x within s)`,

  REWRITE_TAC[CONTINUOUS_WITHIN] THEN
  MESON_TAC[LIM_TRANSFORM_WITHIN; DIST_REFL]);;


let CONTINUOUS_TRANSFORM_AT = 
prove
 (`!f g:real^M->real^N x d.
        &0 < d /\ (!x'. dist(x',x) < d ==> f(x') = g(x')) /\
        f continuous (at x)
        ==> g continuous (at x)`,

  REWRITE_TAC[CONTINUOUS_AT] THEN
  MESON_TAC[LIM_TRANSFORM_AT; DIST_REFL]);;


let CONTINUOUS_TRANSFORM_WITHIN_OPEN = 
prove
 (`!f g:real^M->real^N s a.
        open s /\ a IN s /\
        (!x. x IN s ==> f x = g x) /\
        f continuous at a
        ==> g continuous at a`,


let CONTINUOUS_TRANSFORM_WITHIN_OPEN_IN = 
prove
 (`!f g:real^M->real^N s t a.
        open_in (subtopology euclidean t) s /\ a IN s /\
        (!x. x IN s ==> f x = g x) /\
        f continuous (at a within t)
        ==> g continuous (at a within t)`,

(* ------------------------------------------------------------------------- *)
(* Derive the epsilon-delta forms, which we often use as "definitions"       *)
(* ------------------------------------------------------------------------- *)


let continuous_within = 
prove
 (`f continuous (at x within s) <=>
        !e. &0 < e
            ==> ?d. &0 < d /\
                    !x'. x' IN s /\ dist(x',x) < d ==> dist(f(x'),f(x)) < e`,

  REWRITE_TAC[CONTINUOUS_WITHIN; LIM_WITHIN] THEN
  REWRITE_TAC[GSYM DIST_NZ] THEN MESON_TAC[DIST_REFL]);;


let continuous_at = 
prove
 (`f continuous (at x) <=>
        !e. &0 < e ==> ?d. &0 < d /\
                           !x'. dist(x',x) < d ==> dist(f(x'),f(x)) < e`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[continuous_within; IN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Versions in terms of open balls.                                          *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_BALL = 
prove
 (`!f s x. f continuous (at x within s) <=>
                !e. &0 < e
                    ==> ?d. &0 < d /\
                            IMAGE f (ball(x,d) INTER s) SUBSET ball(f x,e)`,


let CONTINUOUS_AT_BALL = 
prove
 (`!f x. f continuous (at x) <=>
                !e. &0 < e
                    ==> ?d. &0 < d /\
                            IMAGE f (ball(x,d)) SUBSET ball(f x,e)`,

  SIMP_TAC[SUBSET; FORALL_IN_IMAGE; IN_BALL; continuous_at] THEN
  MESON_TAC[DIST_SYM]);;

(* ------------------------------------------------------------------------- *)
(* For setwise continuity, just start from the epsilon-delta definitions.    *)
(* ------------------------------------------------------------------------- *)

parse_as_infix ("continuous_on",(12,"right"));;
parse_as_infix ("uniformly_continuous_on",(12,"right"));;


let continuous_on = new_definition
  `f continuous_on s <=>
        !x. x IN s ==> !e. &0 < e
                           ==> ?d. &0 < d /\
                                   !x'. x' IN s /\ dist(x',x) < d
                                        ==> dist(f(x'),f(x)) < e`;;


let uniformly_continuous_on = new_definition
  `f uniformly_continuous_on s <=>
        !e. &0 < e
            ==> ?d. &0 < d /\
                    !x x'. x IN s /\ x' IN s /\ dist(x',x) < d
                           ==> dist(f(x'),f(x)) < e`;;

(* ------------------------------------------------------------------------- *)
(* Some simple consequential lemmas.                                         *)
(* ------------------------------------------------------------------------- *)


let UNIFORMLY_CONTINUOUS_IMP_CONTINUOUS = 
prove
 (`!f s. f uniformly_continuous_on s ==> f continuous_on s`,

  REWRITE_TAC[uniformly_continuous_on; continuous_on] THEN MESON_TAC[]);;


let CONTINUOUS_AT_IMP_CONTINUOUS_ON = 
prove
 (`!f s. (!x. x IN s ==> f continuous (at x)) ==> f continuous_on s`,

  REWRITE_TAC[continuous_at; continuous_on] THEN MESON_TAC[]);;


let CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN = 
prove
 (`!f s. f continuous_on s <=> !x. x IN s ==> f continuous (at x within s)`,


let CONTINUOUS_ON = 
prove
 (`!f (s:real^N->bool).
        f continuous_on s <=> !x. x IN s ==> (f --> f(x)) (at x within s)`,


let CONTINUOUS_ON_EQ_CONTINUOUS_AT = 
prove
 (`!f:real^M->real^N s.
      open s ==> (f continuous_on s <=> (!x. x IN s ==> f continuous (at x)))`,


let CONTINUOUS_WITHIN_SUBSET = 
prove
 (`!f s t x. f continuous (at x within s) /\ t SUBSET s
             ==> f continuous (at x within t)`,

   REWRITE_TAC[CONTINUOUS_WITHIN] THEN MESON_TAC[LIM_WITHIN_SUBSET]);;


let CONTINUOUS_ON_SUBSET = 
prove
 (`!f s t. f continuous_on s /\ t SUBSET s ==> f continuous_on t`,

  REWRITE_TAC[CONTINUOUS_ON] THEN MESON_TAC[SUBSET; LIM_WITHIN_SUBSET]);;


let UNIFORMLY_CONTINUOUS_ON_SUBSET = 
prove
 (`!f s t. f uniformly_continuous_on s /\ t SUBSET s
           ==> f uniformly_continuous_on t`,

  REWRITE_TAC[uniformly_continuous_on] THEN
  MESON_TAC[SUBSET; LIM_WITHIN_SUBSET]);;


let CONTINUOUS_ON_INTERIOR = 
prove
 (`!f:real^M->real^N s x.
        f continuous_on s /\ x IN interior(s) ==> f continuous at x`,

  REWRITE_TAC[interior; IN_ELIM_THM] THEN
  MESON_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_AT; CONTINUOUS_ON_SUBSET]);;


let CONTINUOUS_ON_EQ = 
prove
 (`!f g s. (!x. x IN s ==> f(x) = g(x)) /\ f continuous_on s
           ==> g continuous_on s`,

  SIMP_TAC[continuous_on; IMP_CONJ]);;


let UNIFORMLY_CONTINUOUS_ON_EQ = 
prove
 (`!f g s.
        (!x. x IN s ==> f x = g x) /\ f uniformly_continuous_on s
        ==> g uniformly_continuous_on s`,


let CONTINUOUS_ON_SING = 
prove
 (`!f:real^M->real^N a. f continuous_on {a}`,

  SIMP_TAC[continuous_on; IN_SING; FORALL_UNWIND_THM2; DIST_REFL] THEN
  MESON_TAC[]);;


let CONTINUOUS_ON_EMPTY = 
prove
 (`!f:real^M->real^N. f continuous_on {}`,


let CONTINUOUS_ON_NO_LIMPT = 
prove
 (`!f:real^M->real^N s.
     ~(?x. x limit_point_of s) ==> f continuous_on s`,

  REWRITE_TAC[continuous_on; LIMPT_APPROACHABLE] THEN MESON_TAC[DIST_REFL]);;


let CONTINUOUS_ON_FINITE = 
prove
 (`!f:real^M->real^N s. FINITE s ==> f continuous_on s`,


let CONTRACTION_IMP_CONTINUOUS_ON = 
prove
 (`!f:real^M->real^N.
        (!x y. x IN s /\ y IN s ==> dist(f x,f y) <= dist(x,y))
        ==> f continuous_on s`,

  SIMP_TAC[continuous_on] THEN MESON_TAC[REAL_LET_TRANS]);;


let ISOMETRY_ON_IMP_CONTINUOUS_ON = 
prove
 (`!f:real^M->real^N.
        (!x y. x IN s /\ y IN s ==> dist(f x,f y) = dist(x,y))
        ==> f continuous_on s`,

(* ------------------------------------------------------------------------- *)
(* Characterization of various kinds of continuity in terms of sequences.    *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_SEQUENTIALLY = 
prove
 (`!f a:real^N.
        f continuous (at a within s) <=>
                !x. (!n. x(n) IN s) /\ (x --> a) sequentially
                     ==> ((f o x) --> f(a)) sequentially`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_within] THEN EQ_TAC THENL
   [REWRITE_TAC[LIM_SEQUENTIALLY; o_THM] THEN MESON_TAC[]; ALL_TAC] THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  DISCH_THEN(MP_TAC o GEN `n:num` o SPEC `&1 / (&n + &1)`) THEN
  SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; REAL_OF_NUM_LE; REAL_POS; ARITH;
       REAL_ARITH `&0 <= n ==> &0 < n + &1`; NOT_FORALL_THM; SKOLEM_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[NOT_IMP; FORALL_AND_THM] THEN
  X_GEN_TAC `y:num->real^N` THEN REWRITE_TAC[LIM_SEQUENTIALLY; o_THM] THEN
  STRIP_TAC THEN CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[LE_REFL]] THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC FORALL_POS_MONO_1 THEN
  CONJ_TAC THENL [ASM_MESON_TAC[REAL_LT_TRANS]; ALL_TAC] THEN
  X_GEN_TAC `n:num` THEN EXISTS_TAC `n:num` THEN X_GEN_TAC `m:num` THEN
  DISCH_TAC THEN MATCH_MP_TAC REAL_LTE_TRANS THEN
  EXISTS_TAC `&1 / (&m + &1)` THEN ASM_REWRITE_TAC[] THEN
  ASM_SIMP_TAC[REAL_LE_INV2; real_div; REAL_ARITH `&0 <= x ==> &0 < x + &1`;
               REAL_POS; REAL_MUL_LID; REAL_LE_RADD; REAL_OF_NUM_LE]);;


let CONTINUOUS_AT_SEQUENTIALLY = 
prove
 (`!f a:real^N.
        f continuous (at a) <=>
              !x. (x --> a) sequentially
                  ==> ((f o x) --> f(a)) sequentially`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[CONTINUOUS_WITHIN_SEQUENTIALLY; IN_UNIV]);;


let CONTINUOUS_ON_SEQUENTIALLY = 
prove
 (`!f s:real^N->bool.
        f continuous_on s <=>
              !x a. a IN s /\ (!n. x(n) IN s) /\ (x --> a) sequentially
                    ==> ((f o x) --> f(a)) sequentially`,


let UNIFORMLY_CONTINUOUS_ON_SEQUENTIALLY = 
prove
 (`!f s:real^N->bool.
        f uniformly_continuous_on s <=>
              !x y. (!n. x(n) IN s) /\ (!n. y(n) IN s) /\
                    ((\n. x(n) - y(n)) --> vec 0) sequentially
                    ==> ((\n. f(x(n)) - f(y(n))) --> vec 0) sequentially`,

  REPEAT GEN_TAC THEN REWRITE_TAC[uniformly_continuous_on] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY; dist; VECTOR_SUB_RZERO] THEN
  EQ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; NOT_EXISTS_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  DISCH_THEN(MP_TAC o GEN `n:num` o SPEC `&1 / (&n + &1)`) THEN
  SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; REAL_OF_NUM_LE; REAL_POS; ARITH;
       REAL_ARITH `&0 <= n ==> &0 < n + &1`; NOT_FORALL_THM; SKOLEM_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `x:num->real^N` THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `y:num->real^N` THEN
  REWRITE_TAC[NOT_IMP; FORALL_AND_THM] THEN STRIP_TAC THEN
  ASM_REWRITE_TAC[] THEN ONCE_REWRITE_TAC[NORM_SUB] THEN CONJ_TAC THENL
   [MATCH_MP_TAC FORALL_POS_MONO_1 THEN
    CONJ_TAC THENL [ASM_MESON_TAC[REAL_LT_TRANS]; ALL_TAC] THEN
    X_GEN_TAC `n:num` THEN EXISTS_TAC `n:num` THEN X_GEN_TAC `m:num` THEN
    DISCH_TAC THEN MATCH_MP_TAC REAL_LTE_TRANS THEN
    EXISTS_TAC `&1 / (&m + &1)` THEN ASM_REWRITE_TAC[] THEN
    ASM_SIMP_TAC[REAL_LE_INV2; real_div; REAL_ARITH `&0 <= x ==> &0 < x + &1`;
                 REAL_POS; REAL_MUL_LID; REAL_LE_RADD; REAL_OF_NUM_LE];
    EXISTS_TAC `e:real` THEN ASM_REWRITE_TAC[] THEN
    EXISTS_TAC `\x:num. x` THEN ASM_REWRITE_TAC[LE_REFL]]);;


let LIM_CONTINUOUS_FUNCTION = 
prove
 (`!f net g l.
        f continuous (at l) /\ (g --> l) net ==> ((\x. f(g x)) --> f l) net`,

  REWRITE_TAC[tendsto; continuous_at; eventually] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Combination results for pointwise continuity.                             *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_CONST = 
prove
 (`!net c. (\x. c) continuous net`,

  REWRITE_TAC[continuous; LIM_CONST]);;


let CONTINUOUS_CMUL = 
prove
 (`!f c net. f continuous net ==> (\x. c % f(x)) continuous net`,

  REWRITE_TAC[continuous; LIM_CMUL]);;


let CONTINUOUS_NEG = 
prove
 (`!f net. f continuous net ==> (\x. --(f x)) continuous net`,

  REWRITE_TAC[continuous; LIM_NEG]);;


let CONTINUOUS_ADD = 
prove
 (`!f g net. f continuous net /\ g continuous net
           ==> (\x. f(x) + g(x)) continuous net`,

  REWRITE_TAC[continuous; LIM_ADD]);;


let CONTINUOUS_SUB = 
prove
 (`!f g net. f continuous net /\ g continuous net
           ==> (\x. f(x) - g(x)) continuous net`,

  REWRITE_TAC[continuous; LIM_SUB]);;


let CONTINUOUS_ABS = 
prove
 (`!(f:A->real^N) net.
        f continuous net
        ==> (\x. (lambda i. abs(f(x)$i)):real^N) continuous net`,

  REWRITE_TAC[continuous; LIM_ABS]);;


let CONTINUOUS_MAX = 
prove
 (`!(f:A->real^N) (g:A->real^N) net.
        f continuous net /\ g continuous net
        ==> (\x. (lambda i. max (f(x)$i) (g(x)$i)):real^N) continuous net`,

  REWRITE_TAC[continuous; LIM_MAX]);;


let CONTINUOUS_MIN = 
prove
 (`!(f:A->real^N) (g:A->real^N) net.
        f continuous net /\ g continuous net
        ==> (\x. (lambda i. min (f(x)$i) (g(x)$i)):real^N) continuous net`,

  REWRITE_TAC[continuous; LIM_MIN]);;


let CONTINUOUS_VSUM = 
prove
 (`!net f s. FINITE s /\ (!a. a IN s ==> (f a) continuous net)
             ==> (\x. vsum s (\a. f a x)) continuous net`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  SIMP_TAC[FORALL_IN_INSERT; NOT_IN_EMPTY; VSUM_CLAUSES;
           CONTINUOUS_CONST; CONTINUOUS_ADD; ETA_AX]);;

(* ------------------------------------------------------------------------- *)
(* Same thing for setwise continuity.                                        *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_ON_CONST = 
prove
 (`!s c. (\x. c) continuous_on s`,


let CONTINUOUS_ON_CMUL = 
prove
 (`!f c s. f continuous_on s ==> (\x. c % f(x)) continuous_on s`,


let CONTINUOUS_ON_NEG = 
prove
 (`!f s. f continuous_on s
         ==> (\x. --(f x)) continuous_on s`,


let CONTINUOUS_ON_ADD = 
prove
 (`!f g s. f continuous_on s /\ g continuous_on s
           ==> (\x. f(x) + g(x)) continuous_on s`,


let CONTINUOUS_ON_SUB = 
prove
 (`!f g s. f continuous_on s /\ g continuous_on s
           ==> (\x. f(x) - g(x)) continuous_on s`,


let CONTINUOUS_ON_ABS = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s
        ==> (\x. (lambda i. abs(f(x)$i)):real^N) continuous_on s`,


let CONTINUOUS_ON_MAX = 
prove
 (`!f:real^M->real^N g:real^M->real^N s.
        f continuous_on s /\ g continuous_on s
        ==> (\x. (lambda i. max (f(x)$i) (g(x)$i)):real^N)
            continuous_on s`,


let CONTINUOUS_ON_MIN = 
prove
 (`!f:real^M->real^N g:real^M->real^N s.
        f continuous_on s /\ g continuous_on s
        ==> (\x. (lambda i. min (f(x)$i) (g(x)$i)):real^N)
            continuous_on s`,


let CONTINUOUS_ON_VSUM = 
prove
 (`!t f s. FINITE s /\ (!a. a IN s ==> (f a) continuous_on t)
             ==> (\x. vsum s (\a. f a x)) continuous_on t`,

(* ------------------------------------------------------------------------- *)
(* Same thing for uniform continuity, using sequential formulations.         *)
(* ------------------------------------------------------------------------- *)


let UNIFORMLY_CONTINUOUS_ON_CONST = 
prove
 (`!s c. (\x. c) uniformly_continuous_on s`,


let LINEAR_UNIFORMLY_CONTINUOUS_ON = 
prove
 (`!f:real^M->real^N s. linear f ==> f uniformly_continuous_on s`,

  REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[uniformly_continuous_on; dist; GSYM LINEAR_SUB] THEN
  FIRST_ASSUM(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC o
        MATCH_MP LINEAR_BOUNDED_POS) THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN EXISTS_TAC `e / B:real` THEN
  ASM_SIMP_TAC[REAL_LT_DIV] THEN
  MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^M`] THEN STRIP_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `B * norm(y - x:real^M)` THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[REAL_LT_RDIV_EQ; REAL_MUL_SYM]);;


let UNIFORMLY_CONTINUOUS_ON_COMPOSE = 
prove
 (`!f g s. f uniformly_continuous_on s /\
           g uniformly_continuous_on (IMAGE f s)
           ==> (g o f) uniformly_continuous_on s`,

  
let lemma = prove
   (`(!y. ((?x. (y = f x) /\ P x) /\ Q y ==> R y)) <=>
     (!x. P x /\ Q (f x) ==> R (f x))`,
    MESON_TAC[]) in
  REPEAT GEN_TAC THEN
  REWRITE_TAC[uniformly_continuous_on; o_THM; IN_IMAGE] THEN
  ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN REWRITE_TAC[lemma] THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c <=> b /\ a /\ c`] THEN
  ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN REWRITE_TAC[lemma] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  MATCH_MP_TAC MONO_FORALL THEN
  X_GEN_TAC `e:real` THEN ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[]);;


let BILINEAR_UNIFORMLY_CONTINUOUS_ON_COMPOSE = 
prove
 (`!f:real^M->real^N g (h:real^N->real^P->real^Q) s.
           f uniformly_continuous_on s /\ g uniformly_continuous_on s /\
           bilinear h /\ bounded(IMAGE f s) /\ bounded(IMAGE g s)
           ==> (\x. h (f x) (g x)) uniformly_continuous_on s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[uniformly_continuous_on; dist] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `!a b c d. (h:real^N->real^P->real^Q) a b - h c d =
              h (a - c) b + h c (b - d)`
   (fun th -> ONCE_REWRITE_TAC[th])
  THENL
   [FIRST_ASSUM(fun th -> REWRITE_TAC[MATCH_MP BILINEAR_LSUB th]) THEN
    FIRST_ASSUM(fun th -> REWRITE_TAC[MATCH_MP BILINEAR_RSUB th]) THEN
    VECTOR_ARITH_TAC;
    ALL_TAC] THEN
  FIRST_X_ASSUM(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC o
    MATCH_MP BILINEAR_BOUNDED_POS) THEN
  UNDISCH_TAC `bounded(IMAGE (g:real^M->real^P) s)` THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
  REWRITE_TAC[BOUNDED_POS; FORALL_IN_IMAGE] THEN
  DISCH_THEN(X_CHOOSE_THEN `B1:real` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `B2:real` STRIP_ASSUME_TAC) THEN
  UNDISCH_TAC `(g:real^M->real^P) uniformly_continuous_on s` THEN
  UNDISCH_TAC `(f:real^M->real^N) uniformly_continuous_on s` THEN
  REWRITE_TAC[uniformly_continuous_on] THEN
  DISCH_THEN(MP_TAC o SPEC `e / &2 / &2 / B / B2`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_HALF; dist] THEN
  DISCH_THEN(X_CHOOSE_THEN `d1:real` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(MP_TAC o SPEC `e / &2 / &2 / B / B1`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_HALF; dist] THEN
  DISCH_THEN(X_CHOOSE_THEN `d2:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `min d1 d2` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^M`] THEN STRIP_TAC THEN
  REPEAT(FIRST_X_ASSUM(MP_TAC o SPECL [`x:real^M`; `y:real^M`])) THEN
  ASM_REWRITE_TAC[] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN EXISTS_TAC
   `B * e / &2 / &2 / B / B2 * B2 + B * B1 * e / &2 / &2 / B / B1` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC(NORM_ARITH
     `norm(x) <= a /\ norm(y) <= b ==> norm(x + y:real^N) <= a + b`) THEN
    CONJ_TAC THEN
    FIRST_X_ASSUM(fun th -> W(MP_TAC o PART_MATCH lhand th o lhand o snd)) THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] REAL_LE_TRANS) THEN
    MATCH_MP_TAC REAL_LE_LMUL THEN ASM_SIMP_TAC[REAL_LT_IMP_LE] THEN
    MATCH_MP_TAC REAL_LE_MUL2 THEN
    ASM_SIMP_TAC[REAL_LT_IMP_LE; NORM_POS_LE];
    ASM_SIMP_TAC[REAL_DIV_RMUL; REAL_DIV_LMUL; REAL_LT_IMP_NZ] THEN
    ASM_REAL_ARITH_TAC]);;


let UNIFORMLY_CONTINUOUS_ON_MUL = 
prove
 (`!f g:real^M->real^N s.
        (lift o f) uniformly_continuous_on s /\ g uniformly_continuous_on s /\
        bounded(IMAGE (lift o f) s) /\ bounded(IMAGE g s)
        ==>  (\x. f x % g x) uniformly_continuous_on s`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL
   [`lift o (f:real^M->real)`; `g:real^M->real^N`;
    `\c (v:real^N). drop c % v`; `s:real^M->bool`]
        BILINEAR_UNIFORMLY_CONTINUOUS_ON_COMPOSE) THEN
  ASM_REWRITE_TAC[o_THM; LIFT_DROP] THEN DISCH_THEN MATCH_MP_TAC THEN
  REWRITE_TAC[bilinear; linear; DROP_ADD; DROP_CMUL] THEN VECTOR_ARITH_TAC);;


let UNIFORMLY_CONTINUOUS_ON_CMUL = 
prove
 (`!f c s. f uniformly_continuous_on s
           ==> (\x. c % f(x)) uniformly_continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[UNIFORMLY_CONTINUOUS_ON_SEQUENTIALLY] THEN
  REPEAT(MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN
  DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_CMUL) THEN
  ASM_SIMP_TAC[VECTOR_SUB_LDISTRIB; VECTOR_MUL_RZERO]);;


let UNIFORMLY_CONTINUOUS_ON_VMUL = 
prove
 (`!s:real^M->bool c v:real^N.
      (lift o c) uniformly_continuous_on s
      ==> (\x. c x % v) uniformly_continuous_on s`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(MP_TAC o ISPEC `\x. (drop x % v:real^N)` o MATCH_MP
   (REWRITE_RULE[IMP_CONJ] UNIFORMLY_CONTINUOUS_ON_COMPOSE)) THEN
  REWRITE_TAC[o_DEF; LIFT_DROP] THEN DISCH_THEN MATCH_MP_TAC THEN
  MATCH_MP_TAC LINEAR_UNIFORMLY_CONTINUOUS_ON THEN
  MATCH_MP_TAC LINEAR_VMUL_DROP THEN REWRITE_TAC[LINEAR_ID]);;


let UNIFORMLY_CONTINUOUS_ON_NEG = 
prove
 (`!f s. f uniformly_continuous_on s
         ==> (\x. --(f x)) uniformly_continuous_on s`,

  ONCE_REWRITE_TAC[VECTOR_NEG_MINUS1] THEN
  REWRITE_TAC[UNIFORMLY_CONTINUOUS_ON_CMUL]);;


let UNIFORMLY_CONTINUOUS_ON_ADD = 
prove
 (`!f g s. f uniformly_continuous_on s /\ g uniformly_continuous_on s
           ==> (\x. f(x) + g(x)) uniformly_continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[UNIFORMLY_CONTINUOUS_ON_SEQUENTIALLY] THEN
  REWRITE_TAC[AND_FORALL_THM] THEN
  REPEAT(MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN
  DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[o_DEF] THEN DISCH_THEN(MP_TAC o MATCH_MP LIM_ADD) THEN
  MATCH_MP_TAC EQ_IMP THEN
  REWRITE_TAC[VECTOR_ADD_LID] THEN AP_THM_TAC THEN BINOP_TAC THEN
  REWRITE_TAC[FUN_EQ_THM] THEN VECTOR_ARITH_TAC);;


let UNIFORMLY_CONTINUOUS_ON_SUB = 
prove
 (`!f g s. f uniformly_continuous_on s /\ g uniformly_continuous_on s
           ==> (\x. f(x) - g(x)) uniformly_continuous_on s`,


let UNIFORMLY_CONTINUOUS_ON_VSUM = 
prove
 (`!t f s. FINITE s /\ (!a. a IN s ==> (f a) uniformly_continuous_on t)
             ==> (\x. vsum s (\a. f a x)) uniformly_continuous_on t`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN
  SIMP_TAC[FORALL_IN_INSERT; NOT_IN_EMPTY; VSUM_CLAUSES;
       UNIFORMLY_CONTINUOUS_ON_CONST; UNIFORMLY_CONTINUOUS_ON_ADD; ETA_AX]);;

(* ------------------------------------------------------------------------- *)
(* Identity function is continuous in every sense.                           *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_ID = 
prove
 (`!a s. (\x. x) continuous (at a within s)`,

  REWRITE_TAC[continuous_within] THEN MESON_TAC[]);;


let CONTINUOUS_AT_ID = 
prove
 (`!a. (\x. x) continuous (at a)`,

  REWRITE_TAC[continuous_at] THEN MESON_TAC[]);;


let CONTINUOUS_ON_ID = 
prove
 (`!s. (\x. x) continuous_on s`,

  REWRITE_TAC[continuous_on] THEN MESON_TAC[]);;


let UNIFORMLY_CONTINUOUS_ON_ID = 
prove
 (`!s. (\x. x) uniformly_continuous_on s`,

  REWRITE_TAC[uniformly_continuous_on] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Continuity of all kinds is preserved under composition.                   *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_COMPOSE = 
prove
 (`!f g x s. f continuous (at x within s) /\
             g continuous (at (f x) within IMAGE f s)
             ==> (g o f) continuous (at x within s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_within; o_THM; IN_IMAGE] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  ASM_MESON_TAC[]);;


let CONTINUOUS_AT_COMPOSE = 
prove
 (`!f g x. f continuous (at x) /\ g continuous (at (f x))
           ==> (g o f) continuous (at x)`,


let CONTINUOUS_ON_COMPOSE = 
prove
 (`!f g s. f continuous_on s /\ g continuous_on (IMAGE f s)
           ==> (g o f) continuous_on s`,

(* ------------------------------------------------------------------------- *)
(* Continuity in terms of open preimages.                                    *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_OPEN = 
prove
 (`!f:real^M->real^N x u.
     f continuous (at x within u) <=>
        !t. open t /\ f(x) IN t
            ==> ?s. open s /\ x IN s /\
                    !x'. x' IN s /\ x' IN u ==> f(x') IN t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_within] THEN EQ_TAC THENL
   [DISCH_TAC THEN X_GEN_TAC `t:real^N->bool` THEN
    DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
    GEN_REWRITE_TAC LAND_CONV [open_def] THEN
    DISCH_THEN(MP_TAC o SPEC `(f:real^M->real^N) x`) THEN
    ASM_MESON_TAC[IN_BALL; DIST_SYM; OPEN_BALL; CENTRE_IN_BALL; DIST_SYM];
    DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `ball((f:real^M->real^N) x,e)`) THEN
    ASM_SIMP_TAC[OPEN_BALL; CENTRE_IN_BALL] THEN
    MESON_TAC[open_def; IN_BALL; REAL_LT_TRANS; DIST_SYM]]);;


let CONTINUOUS_AT_OPEN = 
prove
 (`!f:real^M->real^N x.
     f continuous (at x) <=>
        !t. open t /\ f(x) IN t
            ==> ?s. open s /\ x IN s /\
                    !x'. x' IN s ==> f(x') IN t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_at] THEN EQ_TAC THENL
   [DISCH_TAC THEN X_GEN_TAC `t:real^N->bool` THEN
    DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
    GEN_REWRITE_TAC LAND_CONV [open_def] THEN
    DISCH_THEN(MP_TAC o SPEC `(f:real^M->real^N) x`) THEN
    ASM_MESON_TAC[IN_BALL; DIST_SYM; OPEN_BALL; CENTRE_IN_BALL];
    DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `ball((f:real^M->real^N) x,e)`) THEN
    ASM_SIMP_TAC[OPEN_BALL; CENTRE_IN_BALL] THEN
    MESON_TAC[open_def; IN_BALL; REAL_LT_TRANS; DIST_SYM]]);;


let CONTINUOUS_ON_OPEN_GEN = 
prove
 (`!f:real^M->real^N s t.
    IMAGE f s SUBSET t
    ==> (f continuous_on s <=>
         !u. open_in (subtopology euclidean t) u
             ==> open_in (subtopology euclidean s) {x | x IN s /\ f x IN u})`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[continuous_on] THEN EQ_TAC THENL
   [REWRITE_TAC[open_in; SUBSET; IN_ELIM_THM] THEN
    DISCH_TAC THEN X_GEN_TAC `u:real^N->bool` THEN STRIP_TAC THEN
    CONJ_TAC THENL [ASM_MESON_TAC[DIST_REFL]; ALL_TAC] THEN
    X_GEN_TAC `x:real^M` THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `(f:real^M->real^N) x`) THEN ASM SET_TAC[];
    DISCH_TAC THEN X_GEN_TAC `x:real^M` THEN
    DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o
      SPEC `ball((f:real^M->real^N) x,e) INTER t`) THEN
    ANTS_TAC THENL
     [ASM_MESON_TAC[OPEN_IN_OPEN; INTER_COMM; OPEN_BALL]; ALL_TAC] THEN
    REWRITE_TAC[open_in; SUBSET; IN_INTER; IN_ELIM_THM; IN_BALL; IN_IMAGE] THEN
    REWRITE_TAC[AND_FORALL_THM] THEN DISCH_THEN(MP_TAC o SPEC `x:real^M`) THEN
    RULE_ASSUM_TAC(REWRITE_RULE[SUBSET; FORALL_IN_IMAGE]) THEN
    ASM_MESON_TAC[DIST_REFL; DIST_SYM]]);;


let CONTINUOUS_ON_OPEN = 
prove
 (`!f:real^M->real^N s.
      f continuous_on s <=>
        !t. open_in (subtopology euclidean (IMAGE f s)) t
            ==> open_in (subtopology euclidean s) {x | x IN s /\ f(x) IN t}`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_OPEN_GEN THEN
  REWRITE_TAC[SUBSET_REFL]);;


let CONTINUOUS_OPEN_IN_PREIMAGE_GEN = 
prove
 (`!f:real^M->real^N s t u.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        open_in (subtopology euclidean t) u
        ==> open_in (subtopology euclidean s) {x | x IN s /\ f x IN u}`,

  MESON_TAC[CONTINUOUS_ON_OPEN_GEN]);;


let CONTINUOUS_ON_IMP_OPEN_IN = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\
        open_in (subtopology euclidean (IMAGE f s)) t
        ==> open_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  MESON_TAC[CONTINUOUS_ON_OPEN]);;

(* ------------------------------------------------------------------------- *)
(* Similarly in terms of closed sets.                                        *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_ON_CLOSED_GEN = 
prove
 (`!f:real^M->real^N s t.
    IMAGE f s SUBSET t
    ==> (f continuous_on s <=>
         !u. closed_in (subtopology euclidean t) u
             ==> closed_in (subtopology euclidean s)
                           {x | x IN s /\ f x IN u})`,

  REPEAT STRIP_TAC THEN FIRST_ASSUM(fun th ->
    ONCE_REWRITE_TAC[MATCH_MP CONTINUOUS_ON_OPEN_GEN th]) THEN
  EQ_TAC THEN DISCH_TAC THEN X_GEN_TAC `u:real^N->bool` THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `t DIFF u:real^N->bool`) THENL
   [REWRITE_TAC[closed_in]; REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ]] THEN
  REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[SUBSET_RESTRICT] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]);;


let CONTINUOUS_ON_CLOSED = 
prove
 (`!f:real^M->real^N s.
      f continuous_on s <=>
        !t. closed_in (subtopology euclidean (IMAGE f s)) t
            ==> closed_in (subtopology euclidean s) {x | x IN s /\ f(x) IN t}`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_CLOSED_GEN THEN
  REWRITE_TAC[SUBSET_REFL]);;


let CONTINUOUS_CLOSED_IN_PREIMAGE_GEN = 
prove
 (`!f:real^M->real^N s t u.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        closed_in (subtopology euclidean t) u
        ==> closed_in (subtopology euclidean s) {x | x IN s /\ f x IN u}`,


let CONTINUOUS_ON_IMP_CLOSED_IN = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\
        closed_in (subtopology euclidean (IMAGE f s)) t
        ==> closed_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  MESON_TAC[CONTINUOUS_ON_CLOSED]);;

(* ------------------------------------------------------------------------- *)
(* Half-global and completely global cases.                                  *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_OPEN_IN_PREIMAGE = 
prove
 (`!f s t.
         f continuous_on s /\ open t
         ==> open_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  REPEAT STRIP_TAC THEN ONCE_REWRITE_TAC[SET_RULE
   `x IN s /\ f x IN t <=> x IN s /\ f x IN (t INTER IMAGE f s)`] THEN
  FIRST_ASSUM(MATCH_MP_TAC o REWRITE_RULE[CONTINUOUS_ON_OPEN]) THEN
  ONCE_REWRITE_TAC[INTER_COMM] THEN MATCH_MP_TAC OPEN_IN_OPEN_INTER THEN
  ASM_REWRITE_TAC[]);;


let CONTINUOUS_CLOSED_IN_PREIMAGE = 
prove
 (`!f s t.
         f continuous_on s /\ closed t
         ==> closed_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  REPEAT STRIP_TAC THEN ONCE_REWRITE_TAC[SET_RULE
   `x IN s /\ f x IN t <=> x IN s /\ f x IN (t INTER IMAGE f s)`] THEN
  FIRST_ASSUM(MATCH_MP_TAC o REWRITE_RULE[CONTINUOUS_ON_CLOSED]) THEN
  ONCE_REWRITE_TAC[INTER_COMM] THEN MATCH_MP_TAC CLOSED_IN_CLOSED_INTER THEN
  ASM_REWRITE_TAC[]);;


let CONTINUOUS_OPEN_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
     f continuous_on s /\ open s /\ open t
     ==> open {x | x IN s /\ f(x) IN t}`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONTINUOUS_ON_OPEN]) THEN
  REWRITE_TAC [OPEN_IN_OPEN] THEN
  DISCH_THEN(MP_TAC o SPEC `IMAGE (f:real^M->real^N) s INTER t`) THEN
  ANTS_TAC THENL
   [EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC [];
    STRIP_TAC THEN
    SUBGOAL_THEN `{x | x IN s /\ (f:real^M->real^N) x IN t} =
                 s INTER t'` SUBST1_TAC THENL
    [ASM SET_TAC []; ASM_MESON_TAC [OPEN_INTER]]]);;


let CONTINUOUS_CLOSED_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
     f continuous_on s /\ closed s /\ closed t
     ==> closed {x | x IN s /\ f(x) IN t}`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONTINUOUS_ON_CLOSED]) THEN
  REWRITE_TAC [CLOSED_IN_CLOSED] THEN
  DISCH_THEN(MP_TAC o SPEC `IMAGE (f:real^M->real^N) s INTER t`) THEN
  ANTS_TAC THENL
   [EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC [];
    STRIP_TAC THEN
    SUBGOAL_THEN `{x | x IN s /\ (f:real^M->real^N) x IN t} =
                 s INTER t'` SUBST1_TAC THENL
    [ASM SET_TAC []; ASM_MESON_TAC [CLOSED_INTER]]]);;


let CONTINUOUS_OPEN_PREIMAGE_UNIV = 
prove
 (`!f:real^M->real^N s.
        (!x. f continuous (at x)) /\ open s ==> open {x | f(x) IN s}`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPECL [`f:real^M->real^N`; `(:real^M)`; `s:real^N->bool`]
    CONTINUOUS_OPEN_PREIMAGE) THEN
  ASM_SIMP_TAC[OPEN_UNIV; IN_UNIV; CONTINUOUS_AT_IMP_CONTINUOUS_ON]);;


let CONTINUOUS_CLOSED_PREIMAGE_UNIV = 
prove
 (`!f:real^M->real^N s.
        (!x. f continuous (at x)) /\ closed s ==> closed {x | f(x) IN s}`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPECL [`f:real^M->real^N`; `(:real^M)`; `s:real^N->bool`]
    CONTINUOUS_CLOSED_PREIMAGE) THEN
  ASM_SIMP_TAC[CLOSED_UNIV; IN_UNIV; CONTINUOUS_AT_IMP_CONTINUOUS_ON]);;


let CONTINUOUS_OPEN_IN_PREIMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
    f continuous_on s <=>
    !t. open t ==> open_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  REPEAT GEN_TAC THEN EQ_TAC THEN SIMP_TAC[CONTINUOUS_OPEN_IN_PREIMAGE] THEN
  REWRITE_TAC[CONTINUOUS_ON_OPEN] THEN DISCH_TAC THEN
  X_GEN_TAC `t:real^N->bool` THEN GEN_REWRITE_TAC LAND_CONV [OPEN_IN_OPEN] THEN
  DISCH_THEN(X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `u:real^N->bool`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN SET_TAC[]);;


let CONTINUOUS_CLOSED_IN_PREIMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
    f continuous_on s <=>
    !t. closed t
        ==> closed_in (subtopology euclidean s) {x | x IN s /\ f x IN t}`,

  REPEAT GEN_TAC THEN EQ_TAC THEN SIMP_TAC[CONTINUOUS_CLOSED_IN_PREIMAGE] THEN
  REWRITE_TAC[CONTINUOUS_ON_CLOSED] THEN DISCH_TAC THEN
  X_GEN_TAC `t:real^N->bool` THEN
  GEN_REWRITE_TAC LAND_CONV [CLOSED_IN_CLOSED] THEN
  DISCH_THEN(X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `u:real^N->bool`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Linear functions are (uniformly) continuous on any set.                   *)
(* ------------------------------------------------------------------------- *)


let LINEAR_LIM_0 = 
prove
 (`!f. linear f ==> (f --> vec 0) (at (vec 0))`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[LIM_AT] THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP LINEAR_BOUNDED_POS) THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN EXISTS_TAC `e / B` THEN
  ASM_SIMP_TAC[REAL_LT_DIV] THEN REWRITE_TAC[dist; VECTOR_SUB_RZERO] THEN
  ASM_MESON_TAC[REAL_MUL_SYM; REAL_LET_TRANS; REAL_LT_RDIV_EQ]);;


let LINEAR_CONTINUOUS_AT = 
prove
 (`!f:real^M->real^N a. linear f ==> f continuous (at a)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPEC `\x. (f:real^M->real^N) (a + x) - f(a)` LINEAR_LIM_0) THEN
  ANTS_TAC THENL
   [POP_ASSUM MP_TAC THEN SIMP_TAC[linear] THEN
    REPEAT STRIP_TAC THEN VECTOR_ARITH_TAC;
    ALL_TAC] THEN
  REWRITE_TAC[GSYM LIM_NULL; CONTINUOUS_AT] THEN
  GEN_REWRITE_TAC RAND_CONV [LIM_AT_ZERO] THEN SIMP_TAC[]);;


let LINEAR_CONTINUOUS_WITHIN = 
prove
 (`!f:real^M->real^N s x. linear f ==> f continuous (at x within s)`,


let LINEAR_CONTINUOUS_ON = 
prove
 (`!f:real^M->real^N s. linear f ==> f continuous_on s`,


let LINEAR_CONTINUOUS_COMPOSE = 
prove
 (`!net f:A->real^N g:real^N->real^P.
        f continuous net /\ linear g ==> (\x. g(f x)) continuous net`,

  REWRITE_TAC[continuous; LIM_LINEAR]);;


let LINEAR_CONTINUOUS_ON_COMPOSE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s.
        f continuous_on s /\ linear g ==> (\x. g(f x)) continuous_on s`,


let CONTINUOUS_LIFT_COMPONENT_COMPOSE = 
prove
 (`!net f:A->real^N i. f continuous net ==> (\x. lift(f x$i)) continuous net`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `linear(\x:real^N. lift (x$i))` MP_TAC THENL
   [REWRITE_TAC[LINEAR_LIFT_COMPONENT]; REWRITE_TAC[GSYM IMP_CONJ_ALT]] THEN
  REWRITE_TAC[LINEAR_CONTINUOUS_COMPOSE]);;


let CONTINUOUS_ON_LIFT_COMPONENT_COMPOSE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s
        ==> (\x. lift (f x$i)) continuous_on s`,

(* ------------------------------------------------------------------------- *)
(* Also bilinear functions, in composition form.                             *)
(* ------------------------------------------------------------------------- *)


let BILINEAR_CONTINUOUS_COMPOSE = 
prove
 (`!net f:A->real^M g:A->real^N h:real^M->real^N->real^P.
        f continuous net /\ g continuous net /\ bilinear h
        ==> (\x. h (f x) (g x)) continuous net`,

  REWRITE_TAC[continuous; LIM_BILINEAR]);;


let BILINEAR_CONTINUOUS_ON_COMPOSE = 
prove
 (`!f g h s. f continuous_on s /\ g continuous_on s /\ bilinear h
             ==> (\x. h (f x) (g x)) continuous_on s`,


let BILINEAR_DOT = 
prove
 (`bilinear (\x y:real^N. lift(x dot y))`,

  REWRITE_TAC[bilinear; linear; DOT_LADD; DOT_RADD; DOT_LMUL; DOT_RMUL] THEN
  REWRITE_TAC[LIFT_ADD; LIFT_CMUL]);;


let CONTINUOUS_LIFT_DOT2 = 
prove
 (`!net f g:A->real^N.
        f continuous net /\ g continuous net
        ==> (\x. lift(f x dot g x)) continuous net`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP (MATCH_MP (REWRITE_RULE
   [TAUT `p /\ q /\ r ==> s <=> r ==> p /\ q ==> s`]
  BILINEAR_CONTINUOUS_COMPOSE) BILINEAR_DOT)) THEN REWRITE_TAC[]);;


let CONTINUOUS_ON_LIFT_DOT2 = 
prove
 (`!f:real^M->real^N g s.
        f continuous_on s /\ g continuous_on s
        ==> (\x. lift(f x dot g x)) continuous_on s`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP (MATCH_MP (REWRITE_RULE
   [TAUT `p /\ q /\ r ==> s <=> r ==> p /\ q ==> s`]
  BILINEAR_CONTINUOUS_ON_COMPOSE) BILINEAR_DOT)) THEN REWRITE_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Preservation of compactness and connectedness under continuous function.  *)
(* ------------------------------------------------------------------------- *)


let COMPACT_CONTINUOUS_IMAGE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s /\ compact s ==> compact(IMAGE f s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_on; compact] THEN
  STRIP_TAC THEN X_GEN_TAC `y:num->real^N` THEN
  REWRITE_TAC[IN_IMAGE; SKOLEM_THM; FORALL_AND_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `x:num->real^M` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:num->real^M`) THEN ASM_REWRITE_TAC[] THEN
  ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `r:num->num` THEN
  DISCH_THEN(X_CHOOSE_THEN `l:real^M` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `(f:real^M->real^N) l` THEN ASM_REWRITE_TAC[] THEN
  CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `l:real^M`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIM_SEQUENTIALLY]) THEN
  DISCH_THEN(MP_TAC o SPEC `d:real`) THEN ASM_REWRITE_TAC[o_THM] THEN
  ASM_MESON_TAC[]);;


let COMPACT_TRANSLATION = 
prove
 (`!s a:real^N. compact s ==> compact (IMAGE (\x. a + x) s)`,


let COMPACT_TRANSLATION_EQ = 
prove
 (`!a s. compact (IMAGE (\x:real^N. a + x) s) <=> compact s`,

  REPEAT GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[COMPACT_TRANSLATION] THEN
  DISCH_THEN(MP_TAC o ISPEC `--a:real^N` o MATCH_MP COMPACT_TRANSLATION) THEN
  REWRITE_TAC[GSYM IMAGE_o; o_DEF; IMAGE_ID;
              VECTOR_ARITH `--a + a + x:real^N = x`]);;

add_translation_invariants [COMPACT_TRANSLATION_EQ];;


let COMPACT_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s. compact s /\ linear f ==> compact(IMAGE f s)`,


let COMPACT_LINEAR_IMAGE_EQ = 
prove
 (`!f s. linear f /\ (!x y. f x = f y ==> x = y)
         ==> (compact (IMAGE f s) <=> compact s)`,

  MATCH_ACCEPT_TAC(LINEAR_INVARIANT_RULE COMPACT_LINEAR_IMAGE));;

add_linear_invariants [COMPACT_LINEAR_IMAGE_EQ];;


let CONNECTED_CONTINUOUS_IMAGE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s /\ connected s ==> connected(IMAGE f s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_ON_OPEN] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  REWRITE_TAC[CONNECTED_CLOPEN; NOT_FORALL_THM; NOT_IMP; DE_MORGAN_THM] THEN
  REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(fun th -> MP_TAC(SPEC `t:real^N->bool` th) THEN
    MP_TAC(SPEC `IMAGE (f:real^M->real^N) s DIFF t` th)) THEN
  ASM_REWRITE_TAC[] THEN
  SUBGOAL_THEN `{x | x IN s /\ (f:real^M->real^N) x IN IMAGE f s DIFF t} =
                s DIFF {x | x IN s /\ f x IN t}`
  SUBST1_TAC THENL
   [UNDISCH_TAC `t SUBSET IMAGE (f:real^M->real^N) s` THEN
    REWRITE_TAC[EXTENSION; IN_IMAGE; IN_DIFF; IN_ELIM_THM; SUBSET] THEN
    MESON_TAC[];
    REPEAT STRIP_TAC THEN
    EXISTS_TAC `{x | x IN s /\ (f:real^M->real^N) x IN t}` THEN
    ASM_REWRITE_TAC[] THEN POP_ASSUM_LIST(MP_TAC o end_itlist CONJ) THEN
    REWRITE_TAC[IN_IMAGE; SUBSET; IN_ELIM_THM; NOT_IN_EMPTY; EXTENSION] THEN
    MESON_TAC[]]);;


let CONNECTED_TRANSLATION = 
prove
 (`!a s. connected s ==> connected (IMAGE (\x:real^N. a + x) s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_ADD; CONTINUOUS_ON_ID; CONTINUOUS_ON_CONST]);;


let CONNECTED_TRANSLATION_EQ = 
prove
 (`!a s. connected (IMAGE (\x:real^N. a + x) s) <=> connected s`,

  REPEAT GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[CONNECTED_TRANSLATION] THEN
  DISCH_THEN(MP_TAC o ISPEC `--a:real^N` o MATCH_MP CONNECTED_TRANSLATION) THEN
  REWRITE_TAC[GSYM IMAGE_o; o_DEF; IMAGE_ID;
              VECTOR_ARITH `--a + a + x:real^N = x`]);;

add_translation_invariants [CONNECTED_TRANSLATION_EQ];;


let CONNECTED_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s. connected s /\ linear f ==> connected(IMAGE f s)`,


let CONNECTED_LINEAR_IMAGE_EQ = 
prove
 (`!f s. linear f /\ (!x y. f x = f y ==> x = y)
         ==> (connected (IMAGE f s) <=> connected s)`,

  MATCH_ACCEPT_TAC(LINEAR_INVARIANT_RULE CONNECTED_LINEAR_IMAGE));;

add_linear_invariants [CONNECTED_LINEAR_IMAGE_EQ];;

(* ------------------------------------------------------------------------- *)
(* Preservation properties for pasted sets (Cartesian products).             *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        bounded (s PCROSS t) <=>
        s = {} \/ t = {} \/ bounded s /\ bounded t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[PCROSS] THEN
  ASM_CASES_TAC `s:real^M->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  REWRITE_TAC[SET_RULE `{f x y |x,y| F} = {}`; BOUNDED_EMPTY] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM MEMBER_NOT_EMPTY]) THEN
  REWRITE_TAC[bounded; FORALL_PASTECART; IN_ELIM_PASTECART_THM] THEN
  ASM_MESON_TAC[NORM_LE_PASTECART; REAL_LE_TRANS; NORM_PASTECART_LE;
                REAL_LE_ADD2]);;


let BOUNDED_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
     bounded s /\ bounded t ==> bounded (s PCROSS t)`,

  SIMP_TAC[BOUNDED_PCROSS_EQ]);;


let CLOSED_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        closed (s PCROSS t) <=>
        s = {} \/ t = {} \/ closed s /\ closed t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[PCROSS] THEN MAP_EVERY ASM_CASES_TAC
   [`s:real^M->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[NOT_IN_EMPTY; CLOSED_EMPTY; SET_RULE
   `{f x y |x,y| F} = {}`] THEN
  REWRITE_TAC[CLOSED_SEQUENTIAL_LIMITS; LIM_SEQUENTIALLY] THEN
  REWRITE_TAC[FORALL_PASTECART; IN_ELIM_PASTECART_THM] THEN
  REWRITE_TAC[IN_ELIM_THM; SKOLEM_THM; FORALL_AND_THM] THEN
  ONCE_REWRITE_TAC[GSYM FUN_EQ_THM] THEN
  REWRITE_TAC[LEFT_AND_EXISTS_THM; LEFT_IMP_EXISTS_THM] THEN
  SIMP_TAC[TAUT `((p /\ q) /\ r) /\ s ==> t <=> r ==> p /\ q /\ s ==> t`] THEN
  ONCE_REWRITE_TAC[MESON[]
   `(!a b c d e. P a b c d e) <=> (!d e b c a. P a b c d e)`] THEN
  REWRITE_TAC[FORALL_UNWIND_THM2] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM MEMBER_NOT_EMPTY]) THEN EQ_TAC THENL
   [GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV)
     [TAUT `p ==> q /\ r <=> (p ==> q) /\ (p ==> r)`; FORALL_AND_THM] THEN
    MATCH_MP_TAC MONO_AND THEN CONJ_TAC THENL
     [ALL_TAC; GEN_REWRITE_TAC LAND_CONV [SWAP_FORALL_THM]] THEN
    MATCH_MP_TAC MONO_FORALL THEN REPEAT STRIP_TAC THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN MATCH_MP_TAC(MESON[]
     `(?x. P x (\n. x)) ==> (?s x. P x s)`) THEN
    ASM_MESON_TAC[DIST_PASTECART_CANCEL];
    ONCE_REWRITE_TAC[MESON[]
     `(!x l. P x l) /\ (!y m. Q y m) <=> (!x y l m. P x l /\ Q y m)`] THEN
    REPEAT(MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN
    REWRITE_TAC[dist; PASTECART_SUB] THEN
    ASM_MESON_TAC[NORM_LE_PASTECART; REAL_LET_TRANS]]);;


let CLOSED_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
     closed s /\ closed t ==> closed (s PCROSS t)`,

  SIMP_TAC[CLOSED_PCROSS_EQ]);;


let COMPACT_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        compact (s PCROSS t) <=>
        s = {} \/ t = {} \/ compact s /\ compact t`,


let COMPACT_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
     compact s /\ compact t ==> compact (s PCROSS t)`,

  SIMP_TAC[COMPACT_PCROSS_EQ]);;


let OPEN_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        open (s PCROSS t) <=>
        s = {} \/ t = {} \/ open s /\ open t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[PCROSS] THEN
  ASM_CASES_TAC `s:real^M->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  REWRITE_TAC[SET_RULE `{f x y |x,y| F} = {}`; OPEN_EMPTY] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM MEMBER_NOT_EMPTY]) THEN
  EQ_TAC THENL
   [REWRITE_TAC[open_def; FORALL_PASTECART; IN_ELIM_PASTECART_THM] THEN
    ASM_MESON_TAC[DIST_PASTECART_CANCEL];
    REWRITE_TAC[OPEN_CLOSED] THEN STRIP_TAC THEN
    SUBGOAL_THEN
     `UNIV DIFF {pastecart x y | x IN s /\ y IN t} =
      {pastecart x y | x IN ((:real^M) DIFF s) /\ y IN (:real^N)} UNION
      {pastecart x y | x IN (:real^M) /\ y IN ((:real^N) DIFF t)}`
    SUBST1_TAC THENL
     [REWRITE_TAC[EXTENSION; IN_DIFF; IN_UNION; FORALL_PASTECART; IN_UNIV] THEN
      REWRITE_TAC[IN_ELIM_THM; PASTECART_EQ; FSTCART_PASTECART;
                  SNDCART_PASTECART] THEN MESON_TAC[];
      SIMP_TAC[GSYM PCROSS] THEN MATCH_MP_TAC CLOSED_UNION THEN CONJ_TAC THEN
      MATCH_MP_TAC CLOSED_PCROSS THEN ASM_REWRITE_TAC[CLOSED_UNIV]]]);;


let OPEN_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        open s /\ open t ==> open (s PCROSS t)`,

  SIMP_TAC[OPEN_PCROSS_EQ]);;


let OPEN_IN_PCROSS = 
prove
 (`!s s':real^M->bool t t':real^N->bool.
        open_in (subtopology euclidean s) s' /\
        open_in (subtopology euclidean t) t'
        ==> open_in (subtopology euclidean (s PCROSS t)) (s' PCROSS t')`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_OPEN] THEN DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `s'':real^M->bool` STRIP_ASSUME_TAC)
   (X_CHOOSE_THEN `t'':real^N->bool` STRIP_ASSUME_TAC)) THEN
  EXISTS_TAC `(s'':real^M->bool) PCROSS (t'':real^N->bool)` THEN
  ASM_SIMP_TAC[OPEN_PCROSS; EXTENSION; FORALL_PASTECART] THEN
  REWRITE_TAC[IN_INTER; PASTECART_IN_PCROSS] THEN ASM SET_TAC[]);;


let PASTECART_IN_INTERIOR_SUBTOPOLOGY = 
prove
 (`!s t u x:real^M y:real^N.
     pastecart x y IN u /\ open_in (subtopology euclidean (s PCROSS t)) u
     ==> ?v w. open_in (subtopology euclidean s) v /\ x IN v /\
               open_in (subtopology euclidean t) w /\ y IN w /\
               (v PCROSS w) SUBSET u`,

  REWRITE_TAC[open_in; FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`x:real^M`; `y:real^N`]) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `ball(x:real^M,e / &2) INTER s` THEN
  EXISTS_TAC `ball(y:real^N,e / &2) INTER t` THEN
  SUBGOAL_THEN `(x:real^M) IN s /\ (y:real^N) IN t` STRIP_ASSUME_TAC THENL
   [ASM_MESON_TAC[SUBSET; PASTECART_IN_PCROSS]; ALL_TAC] THEN
  ASM_SIMP_TAC[INTER_SUBSET; IN_INTER; CENTRE_IN_BALL; REAL_HALF] THEN
  REWRITE_TAC[IN_BALL] THEN REPEAT(CONJ_TAC THENL
   [MESON_TAC[REAL_SUB_LT; NORM_ARITH
     `dist(x,y) < e /\ dist(z,y) < e - dist(x,y)
      ==> dist(x:real^N,z) < e`];
    ALL_TAC]) THEN
  REWRITE_TAC[SUBSET; FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
  REWRITE_TAC[IN_BALL; IN_INTER] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_REWRITE_TAC[dist; PASTECART_SUB] THEN
  W(MP_TAC o PART_MATCH lhand NORM_PASTECART_LE o lhand o snd) THEN
  REWRITE_TAC[GSYM(ONCE_REWRITE_RULE[DIST_SYM] dist)] THEN
  ASM_REAL_ARITH_TAC);;


let OPEN_IN_PCROSS_EQ = 
prove
 (`!s s':real^M->bool t t':real^N->bool.
        open_in (subtopology euclidean (s PCROSS t)) (s' PCROSS t') <=>
        s' = {} \/ t' = {} \/
        open_in (subtopology euclidean s) s' /\
        open_in (subtopology euclidean t) t'`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s':real^M->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; OPEN_IN_EMPTY] THEN
  ASM_CASES_TAC `t':real^N->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; OPEN_IN_EMPTY] THEN
  EQ_TAC THEN REWRITE_TAC[OPEN_IN_PCROSS] THEN REPEAT STRIP_TAC THENL
   [ONCE_REWRITE_TAC[OPEN_IN_SUBOPEN] THEN
    X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
    UNDISCH_TAC `~(t':real^N->bool = {})` THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
    DISCH_THEN(X_CHOOSE_TAC `y:real^N`);
    ONCE_REWRITE_TAC[OPEN_IN_SUBOPEN] THEN
    X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
    UNDISCH_TAC `~(s':real^M->bool = {})` THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
    DISCH_THEN(X_CHOOSE_TAC `x:real^M`)] THEN
   MP_TAC(ISPECL
     [`s:real^M->bool`; `t:real^N->bool`;
      `(s':real^M->bool) PCROSS (t':real^N->bool)`;
      `x:real^M`; `y:real^N`] PASTECART_IN_INTERIOR_SUBTOPOLOGY) THEN
  ASM_REWRITE_TAC[SUBSET; FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
  MESON_TAC[]);;


let INTERIOR_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        interior (s PCROSS t) = (interior s) PCROSS (interior t)`,

  REPEAT GEN_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
   [REWRITE_TAC[SUBSET; FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
    MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^N`] THEN DISCH_TAC THEN
    MP_TAC(ISPECL [`(:real^M)`; `(:real^N)`;
         `interior((s:real^M->bool) PCROSS (t:real^N->bool))`;
         `x:real^M`; `y:real^N`] PASTECART_IN_INTERIOR_SUBTOPOLOGY) THEN
    REWRITE_TAC[UNIV_PCROSS_UNIV; SUBTOPOLOGY_UNIV; GSYM OPEN_IN] THEN
    ASM_REWRITE_TAC[OPEN_INTERIOR] THEN STRIP_TAC THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP (MESON[INTERIOR_SUBSET; SUBSET_TRANS]
      `s SUBSET interior t ==> s SUBSET t`)) THEN
    REWRITE_TAC[SUBSET_PCROSS] THEN
    ASM_MESON_TAC[NOT_IN_EMPTY; INTERIOR_MAXIMAL; SUBSET];
    MATCH_MP_TAC INTERIOR_MAXIMAL THEN
    SIMP_TAC[OPEN_PCROSS; OPEN_INTERIOR; PCROSS_MONO; INTERIOR_SUBSET]]);;

(* ------------------------------------------------------------------------- *)
(* Quotient maps are occasionally useful.                                    *)
(* ------------------------------------------------------------------------- *)


let QUASICOMPACT_OPEN_CLOSED = 
prove
 (`!f:real^M->real^N s t.
    IMAGE f s SUBSET t
    ==> ((!u. u SUBSET t
              ==> (open_in (subtopology euclidean s)
                           {x | x IN s /\ f x IN u}
                   ==> open_in (subtopology euclidean t) u)) <=>
         (!u. u SUBSET t
              ==> (closed_in (subtopology euclidean s)
                             {x | x IN s /\ f x IN u}
                   ==> closed_in (subtopology euclidean t) u)))`,

  SIMP_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN
  X_GEN_TAC `u:real^N->bool` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `t DIFF u:real^N->bool`) THEN
  ASM_SIMP_TAC[SET_RULE `u SUBSET t ==> t DIFF (t DIFF u) = u`] THEN
  (ANTS_TAC THENL [SET_TAC[]; REPEAT STRIP_TAC]) THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN REWRITE_TAC[SUBSET_RESTRICT] THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (MESON[]
   `open_in top x ==> x = y ==> open_in top y`)) THEN
  ASM SET_TAC[]);;


let QUOTIENT_MAP_IMP_CONTINUOUS_OPEN = 
prove
 (`!f:real^M->real^N s t.
     IMAGE f s SUBSET t /\
     (!u. u SUBSET t
          ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
               open_in (subtopology euclidean t) u))
     ==> f continuous_on s`,


let QUOTIENT_MAP_IMP_CONTINUOUS_CLOSED = 
prove
 (`!f:real^M->real^N s t.
     IMAGE f s SUBSET t /\
     (!u. u SUBSET t
          ==> (closed_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
               closed_in (subtopology euclidean t) u))
     ==> f continuous_on s`,


let OPEN_MAP_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N s.
    f continuous_on s /\
    (!t. open_in (subtopology euclidean s) t
         ==> open_in (subtopology euclidean (IMAGE f s)) (IMAGE f t))
    ==> !t. t SUBSET IMAGE f s
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN t} <=>
                 open_in (subtopology euclidean (IMAGE f s)) t)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THENL
   [SUBGOAL_THEN
     `t = IMAGE f {x | x IN s /\ (f:real^M->real^N) x IN t}`
    SUBST1_TAC THENL [ASM SET_TAC[]; ASM_SIMP_TAC[]];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONTINUOUS_ON_OPEN]) THEN
    ASM_SIMP_TAC[]]);;


let CLOSED_MAP_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N s.
    f continuous_on s /\
    (!t. closed_in (subtopology euclidean s) t
         ==> closed_in (subtopology euclidean (IMAGE f s)) (IMAGE f t))
    ==> !t. t SUBSET IMAGE f s
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN t} <=>
                 open_in (subtopology euclidean (IMAGE f s)) t)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC
     `s DIFF {x | x IN s /\ (f:real^M->real^N) x IN t}`) THEN
    ANTS_TAC THENL
     [MATCH_MP_TAC CLOSED_IN_DIFF THEN
      ASM_SIMP_TAC[CLOSED_IN_SUBTOPOLOGY_REFL;
                   TOPSPACE_EUCLIDEAN; SUBSET_UNIV];
      REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
      DISCH_THEN(MP_TAC o CONJUNCT2) THEN MATCH_MP_TAC EQ_IMP THEN
      AP_TERM_TAC THEN ASM SET_TAC[]];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONTINUOUS_ON_OPEN]) THEN
    ASM_SIMP_TAC[]]);;


let CONTINUOUS_RIGHT_INVERSE_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N g s t.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        g continuous_on t /\ IMAGE g t SUBSET s /\
        (!y. y IN t ==> f(g y) = y)
        ==> (!u. u SUBSET t
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                 open_in (subtopology euclidean t) u))`,

  REWRITE_TAC[CONTINUOUS_ON_OPEN] THEN REPEAT STRIP_TAC THEN EQ_TAC THENL
   [DISCH_TAC THEN FIRST_ASSUM(MP_TAC o SPEC `(IMAGE (g:real^N->real^M) t)
       INTER
       {x | x IN s /\ (f:real^M->real^N) x IN u}`) THEN
    ANTS_TAC THENL
     [FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_IN_OPEN]) THEN
      REWRITE_TAC[OPEN_IN_OPEN] THEN MATCH_MP_TAC MONO_EXISTS THEN
      ASM SET_TAC[];
      MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]];
    DISCH_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
    SUBGOAL_THEN `IMAGE (f:real^M->real^N) s = t`
     (fun th -> ASM_REWRITE_TAC[th]) THEN
    ASM SET_TAC[]]);;


let CONTINUOUS_LEFT_INVERSE_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N g s.
        f continuous_on s /\ g continuous_on (IMAGE f s) /\
        (!x. x IN s ==> g(f x) = x)
        ==> (!u. u SUBSET (IMAGE f s)
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                 open_in (subtopology euclidean (IMAGE f s)) u))`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC CONTINUOUS_RIGHT_INVERSE_IMP_QUOTIENT_MAP THEN
  EXISTS_TAC `g:real^N->real^M` THEN
  ASM_REWRITE_TAC[] THEN ASM SET_TAC[]);;


let QUOTIENT_MAP_OPEN_CLOSED = 
prove
 (`!f:real^M->real^N s t.
    IMAGE f s SUBSET t
    ==> ((!u. u SUBSET t
              ==> (open_in (subtopology euclidean s)
                           {x | x IN s /\ f x IN u} <=>
                   open_in (subtopology euclidean t) u)) <=>
         (!u. u SUBSET t
              ==> (closed_in (subtopology euclidean s)
                             {x | x IN s /\ f x IN u} <=>
                   closed_in (subtopology euclidean t) u)))`,

  SIMP_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN
  X_GEN_TAC `u:real^N->bool` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `t DIFF u:real^N->bool`) THEN
  ASM_SIMP_TAC[SET_RULE `u SUBSET t ==> t DIFF (t DIFF u) = u`] THEN
  (ANTS_TAC THENL [SET_TAC[]; DISCH_THEN(SUBST1_TAC o SYM)]) THEN
  REWRITE_TAC[SUBSET_RESTRICT] THEN AP_TERM_TAC THEN ASM SET_TAC[]);;


let CONTINUOUS_ON_COMPOSE_QUOTIENT = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
      IMAGE f s SUBSET t /\ IMAGE g t SUBSET u /\
      (!v. v SUBSET t
           ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN v} <=>
                open_in (subtopology euclidean t) v)) /\
      (g o f) continuous_on s
      ==> g continuous_on t`,

  REPEAT GEN_TAC THEN
  REPLICATE_TAC 3 (DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  FIRST_ASSUM(fun th -> REWRITE_TAC[MATCH_MP CONTINUOUS_ON_OPEN_GEN th]) THEN
  SUBGOAL_THEN
   `IMAGE ((g:real^N->real^P) o (f:real^M->real^N)) s SUBSET u`
   (fun th -> REWRITE_TAC[MATCH_MP CONTINUOUS_ON_OPEN_GEN th])
  THENL [REWRITE_TAC[IMAGE_o] THEN ASM SET_TAC[]; DISCH_TAC] THEN
  X_GEN_TAC `v:real^P->bool` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `v:real^P->bool`) THEN
  ASM_REWRITE_TAC[o_THM] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `{x | x IN t /\ (g:real^N->real^P) x IN v}`) THEN
  ASM_REWRITE_TAC[SUBSET_RESTRICT] THEN DISCH_THEN(SUBST1_TAC o SYM) THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (MESON[]
   `open_in top s ==> s = t ==> open_in top t`)) THEN
  ASM SET_TAC[]);;


let LIFT_TO_QUOTIENT_SPACE = 
prove
 (`!f:real^M->real^N h:real^M->real^P s t u.
        IMAGE f s = t /\
        (!v. v SUBSET t
           ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN v} <=>
                open_in (subtopology euclidean t) v)) /\
        h continuous_on s /\ IMAGE h s = u /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> h x = h y)
        ==> ?g. g continuous_on t /\ IMAGE g t = u /\
                !x. x IN s ==> h(x) = g(f x)`,

  REPEAT GEN_TAC THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[FUNCTION_FACTORS_LEFT_GEN] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^N->real^P` THEN
  DISCH_TAC THEN CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  MATCH_MP_TAC CONTINUOUS_ON_COMPOSE_QUOTIENT THEN MAP_EVERY EXISTS_TAC
   [`f:real^M->real^N`; `s:real^M->bool`; `u:real^P->bool`] THEN
  ASM_SIMP_TAC[SUBSET_REFL] THEN CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT]
    CONTINUOUS_ON_EQ)) THEN
  ASM_REWRITE_TAC[o_THM]);;


let QUOTIENT_MAP_COMPOSE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        IMAGE f s SUBSET t /\
        (!v. v SUBSET t
           ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN v} <=>
                open_in (subtopology euclidean t) v)) /\
        (!v. v SUBSET u
           ==> (open_in (subtopology euclidean t) {x | x IN t /\ g x IN v} <=>
                open_in (subtopology euclidean u) v))
        ==> !v. v SUBSET u
                ==> (open_in (subtopology euclidean s)
                             {x | x IN s /\ (g o f) x IN v} <=>
                     open_in (subtopology euclidean u) v)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[o_THM] THEN
  SUBGOAL_THEN
   `{x | x IN s /\ (g:real^N->real^P) ((f:real^M->real^N) x) IN v} =
    {x | x IN s /\ f x IN {x | x IN t /\ g x IN v}}`
  SUBST1_TAC THENL [ASM SET_TAC[]; ASM_SIMP_TAC[SUBSET_RESTRICT]]);;


let QUOTIENT_MAP_FROM_COMPOSITION = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        g continuous_on t /\ IMAGE g t SUBSET u /\
        (!v. v SUBSET u
             ==> (open_in (subtopology euclidean s)
                          {x | x IN s /\ (g o f) x IN v} <=>
                  open_in (subtopology euclidean u) v))
        ==> !v. v SUBSET u
                ==> (open_in (subtopology euclidean t)
                              {x | x IN t /\ g x IN v} <=>
                     open_in (subtopology euclidean u) v)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN STRIP_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `v:real^P->bool`) THEN
    ASM_REWRITE_TAC[o_THM] THEN DISCH_THEN(SUBST1_TAC o SYM) THEN
    SUBGOAL_THEN
     `{x | x IN s /\ (g:real^N->real^P) ((f:real^M->real^N) x) IN v} =
      {x | x IN s /\ f x IN {x | x IN t /\ g x IN v}}`
    SUBST1_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[];
    MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `u:real^P->bool` THEN ASM_REWRITE_TAC[]]);;


let QUOTIENT_MAP_FROM_SUBSET = 
prove
 (`!f:real^M->real^N s t u.
        f continuous_on t /\ IMAGE f t SUBSET u /\
        s SUBSET t /\ IMAGE f s = u /\
        (!v. v SUBSET u
             ==> (open_in (subtopology euclidean s)
                          {x | x IN s /\ f x IN v} <=>
                  open_in (subtopology euclidean u) v))
        ==> !v. v SUBSET u
                ==> (open_in (subtopology euclidean t)
                             {x | x IN t /\ f x IN v} <=>
                     open_in (subtopology euclidean u) v)`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC QUOTIENT_MAP_FROM_COMPOSITION THEN
  MAP_EVERY EXISTS_TAC [`\x:real^M. x`; `s:real^M->bool`] THEN
  ASM_REWRITE_TAC[CONTINUOUS_ON_ID; IMAGE_ID; o_THM]);;


let QUOTIENT_MAP_RESTRICT = 
prove
 (`!f:real^M->real^N s t c.
     IMAGE f s SUBSET t /\
     (!u. u SUBSET t
        ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
             open_in (subtopology euclidean t) u)) /\
     (open_in (subtopology euclidean t) c \/
      closed_in (subtopology euclidean t) c)
     ==> !u. u SUBSET c
             ==> (open_in (subtopology euclidean {x | x IN s /\ f x IN c})
                          {x | x IN {x | x IN s /\ f x IN c} /\ f x IN u} <=>
                  open_in (subtopology euclidean c) u)`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  DISCH_THEN(fun th -> MP_TAC th THEN MP_TAC (MATCH_MP
   (REWRITE_RULE[IMP_CONJ_ALT] QUOTIENT_MAP_IMP_CONTINUOUS_OPEN) th)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^M->real^N) {x | x IN s /\ f x IN c} SUBSET c`
  ASSUME_TAC THENL [SET_TAC[]; ALL_TAC] THEN
  FIRST_X_ASSUM DISJ_CASES_TAC THENL
   [FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET);
    ASM_SIMP_TAC[QUOTIENT_MAP_OPEN_CLOSED] THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET)] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `u:real^N->bool` THEN
  DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN
  (ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  (MATCH_MP_TAC EQ_IMP THEN BINOP_TAC THENL
    [MATCH_MP_TAC(MESON[] `t = s /\ (P s <=> Q s) ==> (P s <=> Q t)`) THEN
     CONJ_TAC THENL [ASM SET_TAC[]; REWRITE_TAC[IN_ELIM_THM]];
     ALL_TAC]) THEN
  (EQ_TAC THENL
    [MATCH_MP_TAC(ONCE_REWRITE_RULE[IMP_CONJ_ALT] OPEN_IN_SUBSET_TRANS) ORELSE
     MATCH_MP_TAC(ONCE_REWRITE_RULE[IMP_CONJ_ALT] CLOSED_IN_SUBSET_TRANS);
     MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] OPEN_IN_TRANS) ORELSE
     MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] CLOSED_IN_TRANS)]) THEN
  (MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE_GEN ORELSE
   MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE_GEN ORELSE ASM_SIMP_TAC[]) THEN
  ASM SET_TAC[]);;


let CONNECTED_MONOTONE_QUOTIENT_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
      f continuous_on s /\ IMAGE f s = t /\
      (!u. u SUBSET t
           ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                open_in (subtopology euclidean t) u)) /\
      (!y. y IN t ==> connected {x | x IN s /\ f x = y}) /\
      connected t
      ==> connected s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[connected; NOT_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`u:real^M->bool`; `v:real^M->bool`] THEN STRIP_TAC THEN
  UNDISCH_TAC `connected(t:real^N->bool)` THEN SIMP_TAC[CONNECTED_OPEN_IN] THEN
  MAP_EVERY EXISTS_TAC
   [`IMAGE (f:real^M->real^N) (s INTER u)`;
    `IMAGE (f:real^M->real^N) (s INTER v)`] THEN
  ASM_REWRITE_TAC[IMAGE_EQ_EMPTY] THEN
  SUBGOAL_THEN
   `IMAGE (f:real^M->real^N) (s INTER u) INTER IMAGE f (s INTER v) = {}`
  ASSUME_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY] THEN
    X_GEN_TAC `y:real^N` THEN STRIP_TAC  THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN
    ANTS_TAC THENL [ASM SET_TAC[]; REWRITE_TAC[connected]] THEN
    MAP_EVERY EXISTS_TAC [`u:real^M->bool`; `v:real^M->bool`] THEN
    ASM SET_TAC[];
    ALL_TAC] THEN
  ONCE_REWRITE_TAC[CONJ_ASSOC] THEN
  CONJ_TAC THENL [CONJ_TAC; ASM SET_TAC[]] THEN
  FIRST_X_ASSUM(fun th ->
   W(MP_TAC o PART_MATCH (rand o rand) th o snd)) THEN
  (ANTS_TAC THENL [ASM SET_TAC[]; DISCH_THEN(SUBST1_TAC o SYM)]) THEN
  MATCH_MP_TAC(MESON[]
   `{x | x IN s /\ f x IN IMAGE f u} = u /\ open_in top u
    ==> open_in top {x | x IN s /\ f x IN IMAGE f u}`) THEN
  ASM_SIMP_TAC[OPEN_IN_OPEN_INTER] THEN ASM SET_TAC[]);;


let CONNECTED_MONOTONE_QUOTIENT_PREIMAGE_GEN = 
prove
 (`!f:real^M->real^N s t c.
      IMAGE f s = t /\
      (!u. u SUBSET t
           ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                open_in (subtopology euclidean t) u)) /\
      (!y. y IN t ==> connected {x | x IN s /\ f x = y}) /\
      (open_in (subtopology euclidean t) c \/
       closed_in (subtopology euclidean t) c) /\
      connected c
      ==> connected {x | x IN s /\ f x IN c}`,

  REPEAT GEN_TAC THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  MATCH_MP_TAC(ONCE_REWRITE_RULE[IMP_CONJ]
   (REWRITE_RULE[CONJ_ASSOC] CONNECTED_MONOTONE_QUOTIENT_PREIMAGE)) THEN
  SUBGOAL_THEN `(c:real^N->bool) SUBSET t` ASSUME_TAC THENL
   [ASM_MESON_TAC[OPEN_IN_IMP_SUBSET; CLOSED_IN_IMP_SUBSET]; ALL_TAC] THEN
  EXISTS_TAC `f:real^M->real^N` THEN REPEAT CONJ_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT]
      QUOTIENT_MAP_IMP_CONTINUOUS_OPEN)) THEN
    ASM_REWRITE_TAC[SUBSET_REFL] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] CONTINUOUS_ON_SUBSET) THEN
    REWRITE_TAC[SUBSET_RESTRICT];
    ASM SET_TAC[];
    MATCH_MP_TAC QUOTIENT_MAP_RESTRICT THEN
    ASM_MESON_TAC[SUBSET_REFL];
    X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN
    ANTS_TAC THENL [ASM SET_TAC[]; MATCH_MP_TAC EQ_IMP] THEN
    AP_TERM_TAC THEN ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* More properties of open and closed maps.                                  *)
(* ------------------------------------------------------------------------- *)


let OPEN_MAP_RESTRICT = 
prove
 (`!f:real^M->real^N s t t'.
        (!u. open_in (subtopology euclidean s) u
             ==> open_in (subtopology euclidean t) (IMAGE f u)) /\
        t' SUBSET t
        ==> !u. open_in (subtopology euclidean {x | x IN s /\ f x IN t'}) u
                ==> open_in (subtopology euclidean t') (IMAGE f u)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_OPEN] THEN
  REWRITE_TAC[LEFT_IMP_EXISTS_THM; IMP_CONJ] THEN
  ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN
  REWRITE_TAC[RIGHT_FORALL_IMP_THM; FORALL_UNWIND_THM2] THEN
  REPEAT DISCH_TAC THEN X_GEN_TAC `c:real^M->bool` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `c:real^M->bool`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN ASM SET_TAC[]);;


let CLOSED_MAP_RESTRICT = 
prove
 (`!f:real^M->real^N s t t'.
        (!u. closed_in (subtopology euclidean s) u
             ==> closed_in (subtopology euclidean t) (IMAGE f u)) /\
        t' SUBSET t
        ==> !u. closed_in (subtopology euclidean {x | x IN s /\ f x IN t'}) u
                ==> closed_in (subtopology euclidean t') (IMAGE f u)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  REWRITE_TAC[LEFT_IMP_EXISTS_THM; IMP_CONJ] THEN
  ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN
  REWRITE_TAC[RIGHT_FORALL_IMP_THM; FORALL_UNWIND_THM2] THEN
  REPEAT DISCH_TAC THEN X_GEN_TAC `c:real^M->bool` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `c:real^M->bool`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN ASM SET_TAC[]);;


let QUOTIENT_MAP_OPEN_MAP_EQ = 
prove
 (`!f:real^M->real^N s t.
       IMAGE f s SUBSET t /\
       (!u. u SUBSET t
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                 open_in (subtopology euclidean t) u))
       ==> ((!k. open_in (subtopology euclidean s) k
                 ==> open_in (subtopology euclidean t) (IMAGE f k)) <=>
            (!k. open_in (subtopology euclidean s) k
                 ==> open_in (subtopology euclidean s)
                               {x | x IN s /\ f x IN IMAGE f k}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN
  X_GEN_TAC `k:real^M->bool` THEN STRIP_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `IMAGE (f:real^M->real^N) k`) THEN
  ASM_SIMP_TAC[IMAGE_SUBSET] THEN DISCH_THEN MATCH_MP_TAC THEN ASM SET_TAC[]);;


let QUOTIENT_MAP_CLOSED_MAP_EQ = 
prove
 (`!f:real^M->real^N s t.
       IMAGE f s SUBSET t /\
       (!u. u SUBSET t
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                 open_in (subtopology euclidean t) u))
       ==> ((!k. closed_in (subtopology euclidean s) k
                 ==> closed_in (subtopology euclidean t) (IMAGE f k)) <=>
            (!k. closed_in (subtopology euclidean s) k
                 ==> closed_in (subtopology euclidean s)
                               {x | x IN s /\ f x IN IMAGE f k}))`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ASM_SIMP_TAC[QUOTIENT_MAP_OPEN_CLOSED] THEN
  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN
  X_GEN_TAC `k:real^M->bool` THEN STRIP_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `IMAGE (f:real^M->real^N) k`) THEN
  ASM_SIMP_TAC[IMAGE_SUBSET] THEN DISCH_THEN MATCH_MP_TAC THEN ASM SET_TAC[]);;


let CLOSED_MAP_IMP_OPEN_MAP = 
prove
 (`!f:real^M->real^N s t.
        IMAGE f s = t /\
        (!u. closed_in (subtopology euclidean s) u
                ==> closed_in (subtopology euclidean t) (IMAGE f u)) /\
        (!u. open_in (subtopology euclidean s) u
             ==> open_in (subtopology euclidean s)
                         {x | x IN s /\ f x IN IMAGE f u})
        ==> (!u. open_in (subtopology euclidean s) u
                 ==> open_in (subtopology euclidean t) (IMAGE f u))`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
    `IMAGE (f:real^M->real^N) u =
     t DIFF IMAGE f (s DIFF {x | x IN s /\ f x IN IMAGE f u})`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN ASM SET_TAC[];
    MATCH_MP_TAC OPEN_IN_DIFF THEN REWRITE_TAC[OPEN_IN_REFL] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    MATCH_MP_TAC CLOSED_IN_DIFF THEN REWRITE_TAC[OPEN_IN_REFL] THEN
    ASM_SIMP_TAC[CLOSED_IN_REFL]]);;


let OPEN_MAP_IMP_CLOSED_MAP = 
prove
 (`!f:real^M->real^N s t.
        IMAGE f s = t /\
        (!u. open_in (subtopology euclidean s) u
                ==> open_in (subtopology euclidean t) (IMAGE f u)) /\
        (!u. closed_in (subtopology euclidean s) u
             ==> closed_in (subtopology euclidean s)
                         {x | x IN s /\ f x IN IMAGE f u})
        ==> (!u. closed_in (subtopology euclidean s) u
                 ==> closed_in (subtopology euclidean t) (IMAGE f u))`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
    `IMAGE (f:real^M->real^N) u =
     t DIFF IMAGE f (s DIFF {x | x IN s /\ f x IN IMAGE f u})`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN ASM SET_TAC[];
    MATCH_MP_TAC CLOSED_IN_DIFF THEN REWRITE_TAC[CLOSED_IN_REFL] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    MATCH_MP_TAC OPEN_IN_DIFF THEN REWRITE_TAC[CLOSED_IN_REFL] THEN
    ASM_SIMP_TAC[OPEN_IN_REFL]]);;


let OPEN_MAP_FROM_COMPOSITION_SURJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s = t /\ IMAGE g t SUBSET u /\
        (!k. open_in (subtopology euclidean s) k
             ==> open_in (subtopology euclidean u) (IMAGE (g o f) k))
        ==> (!k. open_in (subtopology euclidean t) k
                 ==> open_in (subtopology euclidean u) (IMAGE g k))`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `IMAGE g k = IMAGE ((g:real^N->real^P) o (f:real^M->real^N))
                      {x | x IN s /\ f(x) IN k}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
    REWRITE_TAC[IMAGE_o] THEN ASM SET_TAC[];
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[SUBSET_REFL]]);;


let CLOSED_MAP_FROM_COMPOSITION_SURJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s = t /\ IMAGE g t SUBSET u /\
        (!k. closed_in (subtopology euclidean s) k
             ==> closed_in (subtopology euclidean u) (IMAGE (g o f) k))
        ==> (!k. closed_in (subtopology euclidean t) k
                 ==> closed_in (subtopology euclidean u) (IMAGE g k))`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `IMAGE g k = IMAGE ((g:real^N->real^P) o (f:real^M->real^N))
                      {x | x IN s /\ f(x) IN k}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
    REWRITE_TAC[IMAGE_o] THEN ASM SET_TAC[];
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[SUBSET_REFL]]);;


let OPEN_MAP_FROM_COMPOSITION_INJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        IMAGE f s SUBSET t /\ IMAGE g t SUBSET u /\
        g continuous_on t /\ (!x y. x IN t /\ y IN t /\ g x = g y ==> x = y) /\
        (!k. open_in (subtopology euclidean s) k
             ==> open_in (subtopology euclidean u) (IMAGE (g o f) k))
        ==> (!k. open_in (subtopology euclidean s) k
                 ==> open_in (subtopology euclidean t) (IMAGE f k))`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `IMAGE f k = {x | x IN t /\
                    g(x) IN IMAGE ((g:real^N->real^P) o (f:real^M->real^N)) k}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
    REWRITE_TAC[IMAGE_o] THEN ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `u:real^P->bool` THEN ASM_SIMP_TAC[]]);;


let CLOSED_MAP_FROM_COMPOSITION_INJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        IMAGE f s SUBSET t /\ IMAGE g t SUBSET u /\
        g continuous_on t /\ (!x y. x IN t /\ y IN t /\ g x = g y ==> x = y) /\
        (!k. closed_in (subtopology euclidean s) k
             ==> closed_in (subtopology euclidean u) (IMAGE (g o f) k))
        ==> (!k. closed_in (subtopology euclidean s) k
                 ==> closed_in (subtopology euclidean t) (IMAGE f k))`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `IMAGE f k = {x | x IN t /\
                    g(x) IN IMAGE ((g:real^N->real^P) o (f:real^M->real^N)) k}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
    REWRITE_TAC[IMAGE_o] THEN ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `u:real^P->bool` THEN ASM_SIMP_TAC[]]);;


let OPEN_MAP_CLOSED_SUPERSET_PREIMAGE = 
prove
 (`!f:real^M->real^N s t u w.
        (!k. open_in (subtopology euclidean s) k
             ==> open_in (subtopology euclidean t) (IMAGE f k)) /\
        closed_in (subtopology euclidean s) u /\
        w SUBSET t /\ {x | x IN s /\ f(x) IN w} SUBSET u
        ==> ?v. closed_in (subtopology euclidean t) v /\
                w SUBSET v /\
                {x | x IN s /\ f(x) IN v} SUBSET u`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `t DIFF IMAGE (f:real^M->real^N) (s DIFF u)` THEN
  CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  MATCH_MP_TAC CLOSED_IN_DIFF THEN REWRITE_TAC[CLOSED_IN_REFL] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[OPEN_IN_DIFF; OPEN_IN_REFL]);;


let OPEN_MAP_CLOSED_SUPERSET_PREIMAGE_EQ = 
prove
 (`!f:real^M->real^N s t.
       IMAGE f s SUBSET t
       ==> ((!k. open_in (subtopology euclidean s) k
                 ==> open_in (subtopology euclidean t) (IMAGE f k)) <=>
            (!u w. closed_in (subtopology euclidean s) u /\
                   w SUBSET t /\ {x | x IN s /\ f(x) IN w} SUBSET u
                   ==> ?v. closed_in (subtopology euclidean t) v /\
                           w SUBSET v /\ {x | x IN s /\ f(x) IN v} SUBSET u))`,

  REPEAT(STRIP_TAC ORELSE EQ_TAC) THEN
  ASM_SIMP_TAC[OPEN_MAP_CLOSED_SUPERSET_PREIMAGE] THEN
  FIRST_X_ASSUM(MP_TAC o SPECL
   [`s DIFF k:real^M->bool`; `t DIFF IMAGE (f:real^M->real^N) k`]) THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
  ASM_SIMP_TAC[CLOSED_IN_DIFF; CLOSED_IN_REFL] THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `v:real^N->bool` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `IMAGE (f:real^M->real^N) k = t DIFF v` SUBST1_TAC THENL
   [ASM SET_TAC[]; ASM_SIMP_TAC[OPEN_IN_DIFF; OPEN_IN_REFL]]);;


let CLOSED_MAP_OPEN_SUPERSET_PREIMAGE = 
prove
 (`!f:real^M->real^N s t u w.
        (!k. closed_in (subtopology euclidean s) k
             ==> closed_in (subtopology euclidean t) (IMAGE f k)) /\
        open_in (subtopology euclidean s) u /\
        w SUBSET t /\ {x | x IN s /\ f(x) IN w} SUBSET u
        ==> ?v. open_in (subtopology euclidean t) v /\
                w SUBSET v /\
                {x | x IN s /\ f(x) IN v} SUBSET u`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `t DIFF IMAGE (f:real^M->real^N) (s DIFF u)` THEN
  CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  MATCH_MP_TAC OPEN_IN_DIFF THEN REWRITE_TAC[OPEN_IN_REFL] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[CLOSED_IN_DIFF; CLOSED_IN_REFL]);;


let CLOSED_MAP_OPEN_SUPERSET_PREIMAGE_EQ = 
prove
 (`!f:real^M->real^N s t.
       IMAGE f s SUBSET t
       ==> ((!k. closed_in (subtopology euclidean s) k
                 ==> closed_in (subtopology euclidean t) (IMAGE f k)) <=>
            (!u w. open_in (subtopology euclidean s) u /\
                   w SUBSET t /\ {x | x IN s /\ f(x) IN w} SUBSET u
                   ==> ?v. open_in (subtopology euclidean t) v /\
                           w SUBSET v /\ {x | x IN s /\ f(x) IN v} SUBSET u))`,

  REPEAT(STRIP_TAC ORELSE EQ_TAC) THEN
  ASM_SIMP_TAC[CLOSED_MAP_OPEN_SUPERSET_PREIMAGE] THEN
  FIRST_X_ASSUM(MP_TAC o SPECL
   [`s DIFF k:real^M->bool`; `t DIFF IMAGE (f:real^M->real^N) k`]) THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
  ASM_SIMP_TAC[OPEN_IN_DIFF; OPEN_IN_REFL] THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `v:real^N->bool` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `IMAGE (f:real^M->real^N) k = t DIFF v` SUBST1_TAC THENL
   [ASM SET_TAC[]; ASM_SIMP_TAC[CLOSED_IN_DIFF; CLOSED_IN_REFL]]);;


let CLOSED_MAP_OPEN_SUPERSET_PREIMAGE_POINT = 
prove
 (`!f:real^M->real^N s t.
       IMAGE f s SUBSET t
       ==> ((!k. closed_in (subtopology euclidean s) k
                 ==> closed_in (subtopology euclidean t) (IMAGE f k)) <=>
            (!u y. open_in (subtopology euclidean s) u /\
                   y IN t /\ {x | x IN s /\ f(x) = y} SUBSET u
                   ==> ?v. open_in (subtopology euclidean t) v /\
                           y IN v /\ {x | x IN s /\ f(x) IN v} SUBSET u))`,

  REPEAT STRIP_TAC THEN ASM_SIMP_TAC[CLOSED_MAP_OPEN_SUPERSET_PREIMAGE_EQ] THEN
  EQ_TAC THEN DISCH_TAC THENL
   [MAP_EVERY X_GEN_TAC [`u:real^M->bool`; `y:real^N`] THEN
    STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPECL  [`u:real^M->bool`; `{y:real^N}`]) THEN
    ASM_REWRITE_TAC[SING_SUBSET; IN_SING];
    MAP_EVERY X_GEN_TAC [`u:real^M->bool`; `w:real^N->bool`] THEN
    STRIP_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `u:real^M->bool`) THEN
    GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `vv:real^N->real^N->bool` THEN DISCH_TAC THEN
    EXISTS_TAC `UNIONS {(vv:real^N->real^N->bool) y | y IN w}` THEN
    CONJ_TAC THENL
     [MATCH_MP_TAC OPEN_IN_UNIONS THEN REWRITE_TAC[FORALL_IN_GSPEC] THEN
      ASM SET_TAC[];
      REWRITE_TAC[UNIONS_GSPEC] THEN
      CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      REWRITE_TAC[SUBSET; IN_ELIM_THM; RIGHT_AND_EXISTS_THM;
                  LEFT_IMP_EXISTS_THM] THEN
      MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^N`] THEN STRIP_TAC THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN ASM SET_TAC[]]]);;


let CONNECTED_OPEN_MONOTONE_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!c. open_in (subtopology euclidean s) c
             ==> open_in (subtopology euclidean t) (IMAGE f c)) /\
        (!y. y IN t ==> connected {x | x IN s /\ f x = y})
        ==> !c. connected c /\ c SUBSET t
                ==> connected {x | x IN s /\ f x IN c}`,

  REPEAT STRIP_TAC THEN FIRST_ASSUM(MP_TAC o SPEC `c:real^N->bool` o MATCH_MP
   (ONCE_REWRITE_RULE[IMP_CONJ] OPEN_MAP_RESTRICT)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN MP_TAC(ISPECL
   [`f:real^M->real^N`; `{x | x IN s /\ (f:real^M->real^N) x IN c}`]
   OPEN_MAP_IMP_QUOTIENT_MAP) THEN
  SUBGOAL_THEN `IMAGE f {x | x IN s /\ (f:real^M->real^N) x IN c} = c`
  ASSUME_TAC THENL [ASM SET_TAC[]; ASM_REWRITE_TAC[]] THEN ANTS_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
      CONTINUOUS_ON_SUBSET)) THEN SET_TAC[];
    DISCH_TAC] THEN
  MATCH_MP_TAC CONNECTED_MONOTONE_QUOTIENT_PREIMAGE THEN
  MAP_EVERY EXISTS_TAC [`f:real^M->real^N`; `c:real^N->bool`] THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
      CONTINUOUS_ON_SUBSET)) THEN SET_TAC[];
    SIMP_TAC[SET_RULE
     `y IN c ==> {x | x IN {x | x IN s /\ f x IN c} /\ f x = y} =
                 {x | x IN s /\ f x = y}`] THEN
   ASM SET_TAC[]]);;


let CONNECTED_CLOSED_MONOTONE_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!c. closed_in (subtopology euclidean s) c
             ==> closed_in (subtopology euclidean t) (IMAGE f c)) /\
        (!y. y IN t ==> connected {x | x IN s /\ f x = y})
        ==> !c. connected c /\ c SUBSET t
                ==> connected {x | x IN s /\ f x IN c}`,

  REPEAT STRIP_TAC THEN FIRST_ASSUM(MP_TAC o SPEC `c:real^N->bool` o MATCH_MP
   (ONCE_REWRITE_RULE[IMP_CONJ] CLOSED_MAP_RESTRICT)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN MP_TAC(ISPECL
   [`f:real^M->real^N`; `{x | x IN s /\ (f:real^M->real^N) x IN c}`]
   CLOSED_MAP_IMP_QUOTIENT_MAP) THEN
  SUBGOAL_THEN `IMAGE f {x | x IN s /\ (f:real^M->real^N) x IN c} = c`
  ASSUME_TAC THENL [ASM SET_TAC[]; ASM_REWRITE_TAC[]] THEN ANTS_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
      CONTINUOUS_ON_SUBSET)) THEN SET_TAC[];
    DISCH_TAC] THEN
  MATCH_MP_TAC CONNECTED_MONOTONE_QUOTIENT_PREIMAGE THEN
  MAP_EVERY EXISTS_TAC [`f:real^M->real^N`; `c:real^N->bool`] THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
      CONTINUOUS_ON_SUBSET)) THEN SET_TAC[];
    SIMP_TAC[SET_RULE
     `y IN c ==> {x | x IN {x | x IN s /\ f x IN c} /\ f x = y} =
                 {x | x IN s /\ f x = y}`] THEN
   ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Proper maps, including projections out of compact sets.                   *)
(* ------------------------------------------------------------------------- *)


let PROPER_MAP = 
prove
 (`!f:real^M->real^N s t.
    IMAGE f s SUBSET t
    ==> ((!k. k SUBSET t /\ compact k ==> compact {x | x IN s /\ f x IN k}) <=>
         (!k. closed_in (subtopology euclidean s) k
              ==> closed_in (subtopology euclidean t) (IMAGE f k)) /\
         (!a. a IN t ==> compact {x | x IN s /\ f x = a}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [REPEAT STRIP_TAC THENL
     [ALL_TAC;
      ONCE_REWRITE_TAC[SET_RULE `x = a <=> x IN {a}`] THEN
      FIRST_X_ASSUM MATCH_MP_TAC THEN
      ASM_REWRITE_TAC[SING_SUBSET; COMPACT_SING]] THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
    REWRITE_TAC[CLOSED_IN_LIMPT] THEN
    CONJ_TAC THENL [ASM SET_TAC[]; X_GEN_TAC `y:real^N`] THEN
    REWRITE_TAC[LIMPT_SEQUENTIAL_INJ; IN_DELETE] THEN
    REWRITE_TAC[IN_IMAGE; LEFT_AND_EXISTS_THM; SKOLEM_THM] THEN
    ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN
    REWRITE_TAC[GSYM CONJ_ASSOC; FORALL_AND_THM] THEN
    ONCE_REWRITE_TAC[GSYM FUN_EQ_THM] THEN
    REWRITE_TAC[UNWIND_THM2; FUN_EQ_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `x:num->real^M` STRIP_ASSUME_TAC) THEN
    SUBGOAL_THEN
     `~(INTERS {{a | a IN k /\
                     (f:real^M->real^N) a IN
                     (y INSERT IMAGE (\i. f(x(n + i))) (:num))} |
                n IN (:num)} = {})`
    MP_TAC THENL
     [MATCH_MP_TAC COMPACT_FIP THEN CONJ_TAC THENL
       [REWRITE_TAC[FORALL_IN_GSPEC; IN_UNIV] THEN X_GEN_TAC `n:num` THEN
        FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CLOSED_IN_CLOSED]) THEN
        DISCH_THEN(X_CHOOSE_THEN `c:real^M->bool` STRIP_ASSUME_TAC) THEN
        ASM_REWRITE_TAC[SET_RULE
         `{x | x IN s INTER k /\ P x} = k INTER {x | x IN s /\ P x}`] THEN
        MATCH_MP_TAC CLOSED_INTER_COMPACT THEN ASM_REWRITE_TAC[] THEN
        FIRST_X_ASSUM MATCH_MP_TAC THEN
        CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
        MATCH_MP_TAC COMPACT_SEQUENCE_WITH_LIMIT THEN
        FIRST_ASSUM(MP_TAC o SPEC `n:num` o MATCH_MP SEQ_OFFSET) THEN
        REWRITE_TAC[ADD_SYM];
        REWRITE_TAC[SIMPLE_IMAGE; FORALL_FINITE_SUBSET_IMAGE] THEN
        X_GEN_TAC `i:num->bool` THEN STRIP_TAC THEN
        FIRST_ASSUM(MP_TAC o ISPEC `\n:num. n` o MATCH_MP
          UPPER_BOUND_FINITE_SET) THEN
        REWRITE_TAC[] THEN DISCH_THEN(X_CHOOSE_TAC `m:num`) THEN
        REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; INTERS_IMAGE; IN_ELIM_THM] THEN
        EXISTS_TAC `(x:num->real^M) m` THEN
        X_GEN_TAC `p:num` THEN DISCH_TAC THEN
        CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
        REWRITE_TAC[IN_INSERT; IN_IMAGE; IN_UNIV] THEN DISJ2_TAC THEN
        EXISTS_TAC `m - p:num` THEN
        ASM_MESON_TAC[ARITH_RULE `p <= m ==> p + m - p:num = m`]];
      REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN MATCH_MP_TAC MONO_EXISTS THEN
      X_GEN_TAC `x:real^M` THEN
      REWRITE_TAC[INTERS_GSPEC; IN_ELIM_THM; IN_UNIV] THEN
      DISCH_THEN(fun th -> LABEL_TAC "*" th THEN MP_TAC(SPEC `0` th)) THEN
      REWRITE_TAC[ADD_CLAUSES; IN_INSERT; IN_IMAGE; IN_UNIV] THEN
      DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (DISJ_CASES_THEN MP_TAC)) THEN
      ASM_SIMP_TAC[] THEN DISCH_THEN(X_CHOOSE_TAC `i:num`) THEN
      REMOVE_THEN "*" (MP_TAC o SPEC `i + 1`) THEN
      ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
      ASM_REWRITE_TAC[IN_INSERT; IN_IMAGE; IN_UNIV] THEN ARITH_TAC];
    STRIP_TAC THEN X_GEN_TAC `k:real^N->bool` THEN STRIP_TAC THEN
    REWRITE_TAC[COMPACT_EQ_HEINE_BOREL] THEN
    X_GEN_TAC `c:(real^M->bool)->bool` THEN STRIP_TAC THEN
    SUBGOAL_THEN
     `!a. a IN k
          ==> ?g. g SUBSET c /\ FINITE g /\
                  {x | x IN s /\ (f:real^M->real^N) x = a} SUBSET UNIONS g`
    MP_TAC THENL
     [X_GEN_TAC `a:real^N` THEN DISCH_TAC THEN UNDISCH_THEN
       `!a. a IN t ==> compact {x | x IN s /\ (f:real^M->real^N) x = a}`
       (MP_TAC o SPEC `a:real^N`) THEN
      ANTS_TAC THENL [ASM SET_TAC[]; REWRITE_TAC[COMPACT_EQ_HEINE_BOREL]] THEN
      DISCH_THEN MATCH_MP_TAC THEN ASM_REWRITE_TAC[] THEN ASM SET_TAC[];
      GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
      REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
      X_GEN_TAC `uu:real^N->(real^M->bool)->bool` THEN
      DISCH_THEN(LABEL_TAC "*")] THEN
    SUBGOAL_THEN
     `!a. a IN k
          ==> ?v. open v /\ a IN v /\
                 {x | x IN s /\ (f:real^M->real^N) x IN v} SUBSET UNIONS(uu a)`
    MP_TAC THENL
     [REPEAT STRIP_TAC THEN
      UNDISCH_THEN
       `!k. closed_in (subtopology euclidean s) k
            ==> closed_in (subtopology euclidean t)
                          (IMAGE (f:real^M->real^N) k)`
       (MP_TAC o SPEC `(s:real^M->bool) DIFF UNIONS(uu(a:real^N))`) THEN
      SIMP_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN ANTS_TAC THENL
       [CONJ_TAC THENL [SET_TAC[]; ALL_TAC] THEN
        REWRITE_TAC[SET_RULE `s DIFF (s DIFF t) = s INTER t`] THEN
        MATCH_MP_TAC OPEN_IN_OPEN_INTER THEN
        MATCH_MP_TAC OPEN_UNIONS THEN ASM SET_TAC[];
        DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
        REWRITE_TAC[OPEN_IN_OPEN] THEN MATCH_MP_TAC MONO_EXISTS THEN
        X_GEN_TAC `v:real^N->bool` THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
        REPEAT(FIRST_X_ASSUM(MP_TAC o SPEC `a:real^N`)) THEN
        ASM_REWRITE_TAC[] THEN REPEAT
         ((ANTS_TAC THENL [ASM SET_TAC[]; DISCH_TAC]) ORELSE STRIP_TAC)
        THENL [ALL_TAC; ASM SET_TAC[]] THEN
        FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [EXTENSION]) THEN
        DISCH_THEN(MP_TAC o SPEC `a:real^N`) THEN ASM SET_TAC[]];
      GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
      REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
      X_GEN_TAC `vv:real^N->(real^N->bool)` THEN
      DISCH_THEN(LABEL_TAC "+")] THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [COMPACT_EQ_HEINE_BOREL]) THEN
    DISCH_THEN(MP_TAC o SPEC `IMAGE (vv:real^N->(real^N->bool)) k`) THEN
    ANTS_TAC THENL [ASM SET_TAC[]; REWRITE_TAC[LEFT_IMP_EXISTS_THM]] THEN
    ONCE_REWRITE_TAC[TAUT `p /\ q /\ r ==> s <=> q /\ p ==> r ==> s`] THEN
    REWRITE_TAC[FORALL_FINITE_SUBSET_IMAGE] THEN
    X_GEN_TAC `j:real^N->bool` THEN REPEAT STRIP_TAC THEN
    EXISTS_TAC `UNIONS(IMAGE (uu:real^N->(real^M->bool)->bool) j)` THEN
    REPEAT CONJ_TAC THENL
     [ASM SET_TAC[];
      ASM_SIMP_TAC[FINITE_UNIONS; FORALL_IN_IMAGE; FINITE_IMAGE] THEN
      ASM SET_TAC[];
      REWRITE_TAC[UNIONS_IMAGE; SUBSET; IN_UNIONS; IN_ELIM_THM] THEN
      ASM SET_TAC[]]]);;


let COMPACT_CONTINUOUS_IMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y)
        ==> (f continuous_on s <=>
             !t. compact t /\ t SUBSET s ==> compact(IMAGE f t))`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [MESON_TAC[COMPACT_CONTINUOUS_IMAGE; CONTINUOUS_ON_SUBSET]; DISCH_TAC] THEN
  FIRST_X_ASSUM(X_CHOOSE_TAC `g:real^N->real^M` o
    GEN_REWRITE_RULE I [INJECTIVE_ON_LEFT_INVERSE]) THEN
  REWRITE_TAC[CONTINUOUS_ON_CLOSED] THEN
  X_GEN_TAC `u:real^N->bool` THEN DISCH_TAC THEN
  MP_TAC(ISPECL [`g:real^N->real^M`; `IMAGE (f:real^M->real^N) s`;
                 `s:real^M->bool`] PROPER_MAP) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC(TAUT `(q ==> s) /\ p ==> (p <=> q /\ r) ==> s`) THEN
  REPEAT STRIP_TAC THENL
   [SUBGOAL_THEN
     `{x | x IN s /\ (f:real^M->real^N) x IN u} = IMAGE g u`
     (fun th -> ASM_MESON_TAC[th]);
    SUBGOAL_THEN
     `{x | x IN IMAGE f s /\ (g:real^N->real^M) x IN k} = IMAGE f k`
     (fun th -> ASM_SIMP_TAC[th])] THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN ASM SET_TAC[]);;


let PROPER_MAP_FROM_COMPACT = 
prove
 (`!f:real^M->real^N s k.
        f continuous_on s /\ IMAGE f s SUBSET t /\ compact s /\
        closed_in (subtopology euclidean t) k
        ==> compact {x | x IN s /\ f x IN k}`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC CLOSED_IN_COMPACT THEN EXISTS_TAC `s:real^M->bool` THEN
  ASM_MESON_TAC[CONTINUOUS_CLOSED_IN_PREIMAGE_GEN]);;


let PROPER_MAP_COMPOSE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        IMAGE f s SUBSET t /\
        (!k. k SUBSET t /\ compact k ==> compact {x | x IN s /\ f x IN k}) /\
        (!k. k SUBSET u /\ compact k ==> compact {x | x IN t /\ g x IN k})
        ==> !k. k SUBSET u /\ compact k
                ==> compact {x | x IN s /\ (g o f) x IN k}`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[o_THM] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `k:real^P->bool`) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `{x | x IN t /\ (g:real^N->real^P) x IN k}`) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; MATCH_MP_TAC EQ_IMP] THEN
  AP_TERM_TAC THEN ASM SET_TAC[]);;


let PROPER_MAP_FROM_COMPOSITION_LEFT = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s = t /\
        g continuous_on t /\ IMAGE g t SUBSET u /\
        (!k. k SUBSET u /\ compact k
             ==> compact {x | x IN s /\ (g o f) x IN k})
        ==> !k. k SUBSET u /\ compact k ==> compact {x | x IN t /\ g x IN k}`,

  REWRITE_TAC[o_THM] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `k:real^P->bool`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o ISPEC `f:real^M->real^N` o MATCH_MP
   (REWRITE_RULE[IMP_CONJ_ALT] COMPACT_CONTINUOUS_IMAGE)) THEN
  ANTS_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        CONTINUOUS_ON_SUBSET)) THEN SET_TAC[];
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]]);;


let PROPER_MAP_FROM_COMPOSITION_RIGHT = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        g continuous_on t /\ IMAGE g t SUBSET u /\
        (!k. k SUBSET u /\ compact k
             ==> compact {x | x IN s /\ (g o f) x IN k})
        ==> !k. k SUBSET t /\ compact k ==> compact {x | x IN s /\ f x IN k}`,

  
let lemma = prove
   (`!s t. closed_in (subtopology euclidean s) t ==> compact s ==> compact t`,
    MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; BOUNDED_SUBSET;
              CLOSED_IN_CLOSED_EQ]) in
  REWRITE_TAC[o_THM] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `IMAGE (g:real^N->real^P) k`) THEN
  ANTS_TAC THENL
   [CONJ_TAC THENL [ASM SET_TAC[]; MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE] THEN
    ASM_MESON_TAC[CONTINUOUS_ON_SUBSET];
    MATCH_MP_TAC lemma THEN
    MATCH_MP_TAC CLOSED_IN_SUBSET_TRANS THEN
    EXISTS_TAC `s:real^M->bool` THEN
    CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
    MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE_GEN THEN
    EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC CLOSED_SUBSET THEN ASM_SIMP_TAC[COMPACT_IMP_CLOSED]]);;


let PROPER_MAP_FSTCART = 
prove
 (`!s:real^M->bool t:real^N->bool k.
        compact t /\ k SUBSET s /\ compact k
        ==> compact {z | z IN s PCROSS t /\ fstcart z IN k}`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `{z | z IN s PCROSS t /\ fstcart z IN k} =
    (k:real^M->bool) PCROSS (t:real^N->bool)`
   (fun th -> ASM_SIMP_TAC[th; COMPACT_PCROSS]) THEN
  REWRITE_TAC[EXTENSION; FORALL_PASTECART; IN_ELIM_THM;
              PASTECART_IN_PCROSS; FSTCART_PASTECART] THEN
  ASM SET_TAC[]);;


let CLOSED_MAP_FSTCART = 
prove
 (`!s:real^M->bool t:real^N->bool c.
        compact t /\ closed_in (subtopology euclidean (s PCROSS t)) c
        ==> closed_in (subtopology euclidean s) (IMAGE fstcart c)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`fstcart:real^(M,N)finite_sum->real^M`;
                 `(s:real^M->bool) PCROSS (t:real^N->bool)`;
                 `s:real^M->bool`]
        PROPER_MAP) THEN
  ASM_SIMP_TAC[PROPER_MAP_FSTCART; IMAGE_FSTCART_PCROSS] THEN
  ASM SET_TAC[]);;


let PROPER_MAP_SNDCART = 
prove
 (`!s:real^M->bool t:real^N->bool k.
        compact s /\ k SUBSET t /\ compact k
        ==> compact {z | z IN s PCROSS t /\ sndcart z IN k}`,

  REPEAT STRIP_TAC THEN SUBGOAL_THEN
   `{z | z IN s PCROSS t /\ sndcart z IN k} =
    (s:real^M->bool) PCROSS (k:real^N->bool)`
   (fun th -> ASM_SIMP_TAC[th; COMPACT_PCROSS]) THEN
  REWRITE_TAC[EXTENSION; FORALL_PASTECART; IN_ELIM_THM;
              PASTECART_IN_PCROSS; SNDCART_PASTECART] THEN
  ASM SET_TAC[]);;


let CLOSED_MAP_SNDCART = 
prove
 (`!s:real^M->bool t:real^N->bool c.
        compact s /\ closed_in (subtopology euclidean (s PCROSS t)) c
        ==> closed_in (subtopology euclidean t) (IMAGE sndcart c)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`sndcart:real^(M,N)finite_sum->real^N`;
                 `(s:real^M->bool) PCROSS (t:real^N->bool)`;
                 `t:real^N->bool`]
        PROPER_MAP) THEN
  ASM_SIMP_TAC[PROPER_MAP_SNDCART; IMAGE_SNDCART_PCROSS] THEN
  ASM SET_TAC[]);;


let CLOSED_IN_COMPACT_PROJECTION = 
prove
 (`!s:real^M->bool t:real^N->bool u.
    compact s /\ closed_in (subtopology euclidean (s PCROSS t)) u
    ==> closed_in (subtopology euclidean t)
                  {y | ?x. x IN s /\ pastecart x y IN u}`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_MAP_SNDCART) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET o CONJUNCT2) THEN
  REWRITE_TAC[EXTENSION; SUBSET; IN_IMAGE; FORALL_PASTECART; EXISTS_PASTECART;
              PASTECART_IN_PCROSS; IN_ELIM_THM; SNDCART_PASTECART] THEN
  SET_TAC[]);;


let CLOSED_COMPACT_PROJECTION = 
prove
 (`!s:real^M->bool t:real^(M,N)finite_sum->bool.
      compact s /\ closed t ==> closed {y | ?x. x IN s /\ pastecart x y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `{y | ?x:real^M. x IN s /\ pastecart x y IN t} =
    {y | ?x. x IN s /\ pastecart x y IN ((s PCROSS (:real^N)) INTER t)}`
  SUBST1_TAC THENL
   [REWRITE_TAC[PASTECART_IN_PCROSS; IN_UNIV; IN_INTER] THEN SET_TAC[];
    MATCH_MP_TAC CLOSED_IN_CLOSED_TRANS THEN
    EXISTS_TAC `(:real^N)` THEN REWRITE_TAC[CLOSED_UNIV] THEN
    MATCH_MP_TAC CLOSED_IN_COMPACT_PROJECTION THEN
    ASM_REWRITE_TAC[] THEN MATCH_MP_TAC CLOSED_SUBSET THEN
    ASM_SIMP_TAC[CLOSED_INTER; CLOSED_UNIV; CLOSED_PCROSS; COMPACT_IMP_CLOSED;
                 INTER_SUBSET]]);;


let TUBE_LEMMA = 
prove
 (`!s:real^M->bool t:real^N->bool u a.
        compact s /\ ~(s = {}) /\ {pastecart x a | x IN s} SUBSET u /\
        open_in(subtopology euclidean (s PCROSS t)) u
        ==> ?v. open_in (subtopology euclidean t) v /\ a IN v /\
                (s PCROSS v) SUBSET u`,

  REPEAT GEN_TAC THEN REWRITE_TAC[PCROSS] THEN
  REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ] THEN
  REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT; PCROSS]
        CLOSED_IN_COMPACT_PROJECTION)) THEN
  ASM_REWRITE_TAC[IN_ELIM_PASTECART_THM; IN_DIFF] THEN
  REWRITE_TAC[GSYM CONJ_ASSOC] THEN MATCH_MP_TAC(MESON[]
   `(closed_in top t ==> s DIFF (s DIFF t) = t) /\
    s DIFF t SUBSET s /\ P(s DIFF t)
    ==> closed_in top t
        ==> ?v. v SUBSET s /\ closed_in top (s DIFF v) /\ P v`) THEN
  REWRITE_TAC[SET_RULE `s DIFF (s DIFF t) = t <=> t SUBSET s`] THEN
  REWRITE_TAC[SUBSET_DIFF] THEN
  SIMP_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
  REWRITE_TAC[IN_DIFF; IN_ELIM_THM] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_GSPEC] THEN
  CONJ_TAC THENL [ALL_TAC; MESON_TAC[]] THEN
  REPEAT(FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [SUBSET])) THEN
  REWRITE_TAC[FORALL_IN_GSPEC; IN_SING; FORALL_PASTECART] THEN
  REWRITE_TAC[IN_ELIM_PASTECART_THM] THEN ASM_MESON_TAC[MEMBER_NOT_EMPTY]);;


let TUBE_LEMMA_GEN = 
prove
 (`!s t t' u:real^(M,N)finite_sum->bool.
        compact s /\ ~(s = {}) /\ t SUBSET t' /\
        s PCROSS t SUBSET u /\
        open_in (subtopology euclidean (s PCROSS t')) u
        ==> ?v. open_in (subtopology euclidean t') v /\
                t SUBSET v /\
                s PCROSS v SUBSET u`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `!a. a IN t ==> ?v. open_in (subtopology euclidean t') v /\ a IN v /\
                       (s:real^M->bool) PCROSS (v:real^N->bool) SUBSET u`
  MP_TAC THENL
   [REPEAT STRIP_TAC THEN MATCH_MP_TAC TUBE_LEMMA THEN
    ASM_REWRITE_TAC[SUBSET; FORALL_IN_GSPEC] THEN REPEAT STRIP_TAC THEN
    REPEAT STRIP_TAC THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o REWRITE_RULE[SUBSET]) THEN
    ASM_REWRITE_TAC[PASTECART_IN_PCROSS];
    GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `vv:real^N->real^N->bool` THEN DISCH_TAC THEN
    EXISTS_TAC `UNIONS (IMAGE (vv:real^N->real^N->bool) t)` THEN
    ASM_SIMP_TAC[OPEN_IN_UNIONS; FORALL_IN_IMAGE] THEN
    REWRITE_TAC[SUBSET; UNIONS_IMAGE; IN_ELIM_THM; FORALL_IN_PCROSS] THEN
    CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    MAP_EVERY X_GEN_TAC [`a:real^M`; `b:real^N`] THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (X_CHOOSE_TAC `c:real^N`)) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N`) THEN
    ASM_REWRITE_TAC[SUBSET; FORALL_IN_PCROSS] THEN ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Pasting functions together on open sets.                                  *)
(* ------------------------------------------------------------------------- *)


let PASTING_LEMMA = 
prove
 (`!f:A->real^M->real^N g t s k.
        (!i. i IN k
             ==> open_in (subtopology euclidean s) (t i) /\
                 (f i) continuous_on (t i)) /\
        (!i j x. i IN k /\ j IN k /\ x IN s INTER t i INTER t j
                 ==> f i x = f j x) /\
        (!x. x IN s ==> ?j. j IN k /\ x IN t j /\ g x = f j x)
        ==> g continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_OPEN_IN_PREIMAGE_EQ] THEN
  STRIP_TAC THEN X_GEN_TAC `u:real^N->bool` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ g x IN u} =
    UNIONS {{x | x IN (t i) /\ ((f:A->real^M->real^N) i x) IN u} |
            i IN k}`
  SUBST1_TAC THENL
   [SUBGOAL_THEN `!i. i IN k ==> ((t:A->real^M->bool) i) SUBSET s`
    ASSUME_TAC THENL
     [ASM_MESON_TAC[OPEN_IN_SUBSET; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY];
      REWRITE_TAC[UNIONS_GSPEC] THEN ASM SET_TAC[]];
    MATCH_MP_TAC OPEN_IN_UNIONS THEN REWRITE_TAC[FORALL_IN_GSPEC] THEN
    ASM_MESON_TAC[OPEN_IN_TRANS]]);;


let PASTING_LEMMA_EXISTS = 
prove
 (`!f:A->real^M->real^N t s k.
        s SUBSET UNIONS {t i | i IN k} /\
        (!i. i IN k
             ==> open_in (subtopology euclidean s) (t i) /\
                 (f i) continuous_on (t i)) /\
        (!i j x. i IN k /\ j IN k /\ x IN s INTER t i INTER t j
                 ==> f i x = f j x)
        ==> ?g. g continuous_on s /\
                (!x i. i IN k /\ x IN s INTER t i ==> g x = f i x)`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `\x. (f:A->real^M->real^N)(@i. i IN k /\ x IN t i) x` THEN
  CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN MATCH_MP_TAC PASTING_LEMMA THEN
  MAP_EVERY EXISTS_TAC
   [`f:A->real^M->real^N`; `t:A->real^M->bool`; `k:A->bool`] THEN
  ASM SET_TAC[]);;


let CONTINUOUS_ON_UNION_LOCAL_OPEN = 
prove
 (`!f:real^M->real^N s.
        open_in (subtopology euclidean (s UNION t)) s /\
        open_in (subtopology euclidean (s UNION t)) t /\
        f continuous_on s /\ f continuous_on t
        ==> f continuous_on (s UNION t)`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPECL
   [`\i:(real^M->bool). (f:real^M->real^N)`; `f:real^M->real^N`;
    `\i:(real^M->bool). i`; `s UNION t:real^M->bool`; `{s:real^M->bool,t}`]
   PASTING_LEMMA) THEN DISCH_THEN MATCH_MP_TAC THEN
  ASM_REWRITE_TAC[FORALL_IN_INSERT; EXISTS_IN_INSERT; NOT_IN_EMPTY] THEN
  REWRITE_TAC[IN_UNION]);;


let CONTINUOUS_ON_UNION_OPEN = 
prove
 (`!f s t. open s /\ open t /\ f continuous_on s /\ f continuous_on t
           ==> f continuous_on (s UNION t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_UNION_LOCAL_OPEN THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC OPEN_OPEN_IN_TRANS THEN
  ASM_SIMP_TAC[OPEN_UNION] THEN SET_TAC[]);;


let CONTINUOUS_ON_CASES_LOCAL_OPEN = 
prove
 (`!P f g:real^M->real^N s t.
        open_in (subtopology euclidean (s UNION t)) s /\
        open_in (subtopology euclidean (s UNION t)) t /\
        f continuous_on s /\ g continuous_on t /\
        (!x. x IN s /\ ~P x \/ x IN t /\ P x ==> f x = g x)
        ==> (\x. if P x then f x else g x) continuous_on (s UNION t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_UNION_LOCAL_OPEN THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_EQ THENL
   [EXISTS_TAC `f:real^M->real^N`; EXISTS_TAC `g:real^M->real^N`] THEN
  ASM_REWRITE_TAC[] THEN ASM_MESON_TAC[]);;


let CONTINUOUS_ON_CASES_OPEN = 
prove
 (`!P f g s t.
           open s /\
           open t /\
           f continuous_on s /\
           g continuous_on t /\
           (!x. x IN s /\ ~P x \/ x IN t /\ P x ==> f x = g x)
           ==> (\x. if P x then f x else g x) continuous_on s UNION t`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_CASES_LOCAL_OPEN THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC OPEN_OPEN_IN_TRANS THEN
  ASM_SIMP_TAC[OPEN_UNION] THEN SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Likewise on closed sets, with a finiteness assumption.                    *)
(* ------------------------------------------------------------------------- *)


let PASTING_LEMMA_CLOSED = 
prove
 (`!f:A->real^M->real^N g t s k.
        FINITE k /\
        (!i. i IN k
             ==> closed_in (subtopology euclidean s) (t i) /\
                 (f i) continuous_on (t i)) /\
        (!i j x. i IN k /\ j IN k /\ x IN s INTER t i INTER t j
                 ==> f i x = f j x) /\
        (!x. x IN s ==> ?j. j IN k /\ x IN t j /\ g x = f j x)
        ==> g continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_CLOSED_IN_PREIMAGE_EQ] THEN
  STRIP_TAC THEN X_GEN_TAC `u:real^N->bool` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ g x IN u} =
    UNIONS {{x | x IN (t i) /\ ((f:A->real^M->real^N) i x) IN u} |
            i IN k}`
  SUBST1_TAC THENL
   [SUBGOAL_THEN `!i. i IN k ==> ((t:A->real^M->bool) i) SUBSET s`
    ASSUME_TAC THENL
     [ASM_MESON_TAC[CLOSED_IN_SUBSET; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY];
      REWRITE_TAC[UNIONS_GSPEC] THEN ASM SET_TAC[]];
    MATCH_MP_TAC CLOSED_IN_UNIONS THEN
    ASM_SIMP_TAC[SIMPLE_IMAGE; FINITE_IMAGE; FORALL_IN_IMAGE] THEN
    ASM_MESON_TAC[CLOSED_IN_TRANS]]);;


let PASTING_LEMMA_EXISTS_CLOSED = 
prove
 (`!f:A->real^M->real^N t s k.
        FINITE k /\
        s SUBSET UNIONS {t i | i IN k} /\
        (!i. i IN k
             ==> closed_in (subtopology euclidean s) (t i) /\
                 (f i) continuous_on (t i)) /\
        (!i j x. i IN k /\ j IN k /\ x IN s INTER t i INTER t j
                 ==> f i x = f j x)
        ==> ?g. g continuous_on s /\
                (!x i. i IN k /\ x IN s INTER t i ==> g x = f i x)`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `\x. (f:A->real^M->real^N)(@i. i IN k /\ x IN t i) x` THEN
  CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  MATCH_MP_TAC PASTING_LEMMA_CLOSED THEN
  MAP_EVERY EXISTS_TAC
   [`f:A->real^M->real^N`; `t:A->real^M->bool`; `k:A->bool`] THEN
  ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Closure of halflines, halfspaces and hyperplanes.                         *)
(* ------------------------------------------------------------------------- *)


let LIM_LIFT_DOT = 
prove
 (`!f:real^M->real^N a.
        (f --> l) net ==> ((lift o (\y. a dot f(y))) --> lift(a dot l)) net`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `a = vec 0:real^N` THENL
   [ASM_REWRITE_TAC[DOT_LZERO; LIFT_NUM; o_DEF; LIM_CONST]; ALL_TAC] THEN
  REWRITE_TAC[LIM] THEN MATCH_MP_TAC MONO_OR THEN REWRITE_TAC[] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / norm(a:real^N)`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; NORM_POS_LT; REAL_LT_RDIV_EQ] THEN
  REWRITE_TAC[dist; o_THM; GSYM LIFT_SUB; GSYM DOT_RSUB; NORM_LIFT] THEN
  ONCE_REWRITE_TAC[DOT_SYM] THEN
  MESON_TAC[NORM_CAUCHY_SCHWARZ_ABS; REAL_MUL_SYM; REAL_LET_TRANS]);;


let CONTINUOUS_AT_LIFT_DOT = 
prove
 (`!a:real^N x. (lift o (\y. a dot y)) continuous at x`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_AT; o_THM] THEN
  MATCH_MP_TAC LIM_LIFT_DOT THEN REWRITE_TAC[LIM_AT] THEN MESON_TAC[]);;


let CONTINUOUS_ON_LIFT_DOT = 
prove
 (`!s. (lift o (\y. a dot y)) continuous_on s`,


let CLOSED_INTERVAL_LEFT = 
prove
 (`!b:real^N.
     closed {x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> x$i <= b$i}`,

  REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE; IN_ELIM_THM] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `(x:real^N)$i - (b:real^N)$i`) THEN
  ASM_REWRITE_TAC[REAL_SUB_LT] THEN
  DISCH_THEN(X_CHOOSE_THEN `z:real^N` MP_TAC) THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[dist; REAL_NOT_LT] THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `abs((z - x :real^N)$i)` THEN
  ASM_SIMP_TAC[COMPONENT_LE_NORM] THEN
  ASM_SIMP_TAC[VECTOR_SUB_COMPONENT] THEN
  ASM_SIMP_TAC[REAL_ARITH `z <= b /\ b < x ==> x - b <= abs(z - x)`]);;


let CLOSED_INTERVAL_RIGHT = 
prove
 (`!a:real^N.
     closed {x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= x$i}`,

  REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE; IN_ELIM_THM] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `(a:real^N)$i - (x:real^N)$i`) THEN
  ASM_REWRITE_TAC[REAL_SUB_LT] THEN
  DISCH_THEN(X_CHOOSE_THEN `z:real^N` MP_TAC) THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[dist; REAL_NOT_LT] THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `abs((z - x :real^N)$i)` THEN
  ASM_SIMP_TAC[COMPONENT_LE_NORM] THEN
  ASM_SIMP_TAC[VECTOR_SUB_COMPONENT] THEN
  ASM_SIMP_TAC[REAL_ARITH `x < a /\ a <= z ==> a - x <= abs(z - x)`]);;


let CLOSED_HALFSPACE_LE = 
prove
 (`!a:real^N b. closed {x | a dot x <= b}`,

  REPEAT GEN_TAC THEN
  MP_TAC(ISPEC `(:real^N)` CONTINUOUS_ON_LIFT_DOT) THEN
  REWRITE_TAC[CONTINUOUS_ON_CLOSED; GSYM CLOSED_IN; SUBTOPOLOGY_UNIV] THEN
  DISCH_THEN(MP_TAC o SPEC
   `IMAGE lift {r | ?x:real^N. (a dot x = r) /\ r <= b}`) THEN
  ANTS_TAC THENL
   [ALL_TAC;
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
    REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE; IN_UNIV] THEN
    REWRITE_TAC[o_DEF] THEN MESON_TAC[LIFT_DROP]] THEN
  REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  EXISTS_TAC `{x | !i. 1 <= i /\ i <= dimindex(:1)
                       ==> (x:real^1)$i <= (lift b)$i}` THEN
  REWRITE_TAC[CLOSED_INTERVAL_LEFT] THEN
  SIMP_TAC[EXTENSION; IN_IMAGE; IN_UNIV; IN_ELIM_THM; IN_INTER;
    VEC_COMPONENT; DIMINDEX_1; LAMBDA_BETA; o_THM] THEN
  SIMP_TAC[ARITH_RULE `1 <= i /\ i <= 1 <=> (i = 1)`] THEN
  REWRITE_TAC[GSYM drop; LEFT_FORALL_IMP_THM; EXISTS_REFL] THEN
  MESON_TAC[LIFT_DROP]);;


let CLOSED_HALFSPACE_GE = 
prove
 (`!a:real^N b. closed {x | a dot x >= b}`,

  REWRITE_TAC[REAL_ARITH `a >= b <=> --a <= --b`] THEN
  REWRITE_TAC[GSYM DOT_LNEG; CLOSED_HALFSPACE_LE]);;


let CLOSED_HYPERPLANE = 
prove
 (`!a b. closed {x | a dot x = b}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN
  REWRITE_TAC[REAL_ARITH `b <= a dot x <=> a dot x >= b`] THEN
  REWRITE_TAC[SET_RULE `{x | P x /\ Q x} = {x | P x} INTER {x | Q x}`] THEN
  SIMP_TAC[CLOSED_INTER; CLOSED_HALFSPACE_LE; CLOSED_HALFSPACE_GE]);;


let CLOSED_STANDARD_HYPERPLANE = 
prove
 (`!k a. closed {x:real^N | x$k = a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] CLOSED_HYPERPLANE) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;


let CLOSED_HALFSPACE_COMPONENT_LE = 
prove
 (`!a k. closed {x:real^N | x$k <= a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] CLOSED_HALFSPACE_LE) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;


let CLOSED_HALFSPACE_COMPONENT_GE = 
prove
 (`!a k. closed {x:real^N | x$k >= a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] CLOSED_HALFSPACE_GE) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;

(* ------------------------------------------------------------------------- *)
(* Openness of halfspaces.                                                   *)
(* ------------------------------------------------------------------------- *)


let OPEN_HALFSPACE_LT = 
prove
 (`!a b. open {x | a dot x < b}`,

  REWRITE_TAC[GSYM REAL_NOT_LE] THEN
  REWRITE_TAC[SET_RULE `{x | ~p x} = UNIV DIFF {x | p x}`] THEN
  REWRITE_TAC[GSYM closed; GSYM real_ge; CLOSED_HALFSPACE_GE]);;


let OPEN_HALFSPACE_COMPONENT_LT = 
prove
 (`!a k. open {x:real^N | x$k < a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] OPEN_HALFSPACE_LT) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;


let OPEN_HALFSPACE_GT = 
prove
 (`!a b. open {x | a dot x > b}`,

  REWRITE_TAC[REAL_ARITH `x > y <=> ~(x <= y)`] THEN
  REWRITE_TAC[SET_RULE `{x | ~p x} = UNIV DIFF {x | p x}`] THEN
  REWRITE_TAC[GSYM closed; CLOSED_HALFSPACE_LE]);;


let OPEN_HALFSPACE_COMPONENT_GT = 
prove
 (`!a k. open {x:real^N | x$k > a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] OPEN_HALFSPACE_GT) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;


let OPEN_POSITIVE_MULTIPLES = 
prove
 (`!s:real^N->bool. open s ==> open {c % x | &0 < c /\ x IN s}`,

  REWRITE_TAC[open_def; FORALL_IN_GSPEC] THEN GEN_TAC THEN DISCH_TAC THEN
  MAP_EVERY X_GEN_TAC [`c:real`; `x:real^N`] THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `c * e:real` THEN ASM_SIMP_TAC[REAL_LT_MUL] THEN
  X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `inv(c) % y:real^N`) THEN ANTS_TAC THENL
   [SUBGOAL_THEN `x:real^N = inv c % c % x` SUBST1_TAC THENL
     [ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; VECTOR_MUL_LID;
                   REAL_LT_IMP_NZ];
      ASM_SIMP_TAC[DIST_MUL; real_abs; REAL_LT_INV_EQ; REAL_LT_IMP_LE] THEN
      ONCE_REWRITE_TAC[REAL_ARITH `inv c * x:real = x / c`] THEN
      ASM_MESON_TAC[REAL_LT_LDIV_EQ; REAL_MUL_SYM]];
    DISCH_TAC THEN REWRITE_TAC[IN_ELIM_THM] THEN
    EXISTS_TAC `c:real` THEN EXISTS_TAC `inv(c) % y:real^N` THEN
    ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_RINV; REAL_LT_IMP_NZ] THEN
    VECTOR_ARITH_TAC]);;


let OPEN_INTERVAL_LEFT = 
prove
 (`!b:real^N. open {x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> x$i < b$i}`,

  GEN_TAC THEN
  SUBGOAL_THEN
   `{x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> x$i < b$i} =
    INTERS{{x | x$i < (b:real^N)$i} | i IN 1..dimindex(:N)}`
  SUBST1_TAC THENL
   [REWRITE_TAC[INTERS_GSPEC; IN_NUMSEG] THEN SET_TAC[];
    MATCH_MP_TAC OPEN_INTERS THEN
    SIMP_TAC[SIMPLE_IMAGE; FINITE_IMAGE; FINITE_NUMSEG] THEN
    REWRITE_TAC[FORALL_IN_IMAGE; OPEN_HALFSPACE_COMPONENT_LT]]);;


let OPEN_INTERVAL_RIGHT = 
prove
 (`!a:real^N. open {x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> a$i < x$i}`,

  GEN_TAC THEN
  SUBGOAL_THEN
   `{x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> a$i < x$i} =
    INTERS{{x | (a:real^N)$i < x$i} | i IN 1..dimindex(:N)}`
  SUBST1_TAC THENL
   [REWRITE_TAC[INTERS_GSPEC; IN_NUMSEG] THEN SET_TAC[];
    MATCH_MP_TAC OPEN_INTERS THEN
    SIMP_TAC[SIMPLE_IMAGE; FINITE_IMAGE; FINITE_NUMSEG] THEN
    REWRITE_TAC[FORALL_IN_IMAGE; GSYM real_gt; OPEN_HALFSPACE_COMPONENT_GT]]);;


let OPEN_POSITIVE_ORTHANT = 
prove
 (`open {x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> &0 < x$i}`,

  MP_TAC(ISPEC `vec 0:real^N` OPEN_INTERVAL_RIGHT) THEN
  REWRITE_TAC[VEC_COMPONENT]);;

(* ------------------------------------------------------------------------- *)
(* Closures and interiors of halfspaces.                                     *)
(* ------------------------------------------------------------------------- *)


let INTERIOR_HALFSPACE_LE = 
prove
 (`!a:real^N b.
        ~(a = vec 0) ==> interior {x | a dot x <= b} = {x | a dot x < b}`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INTERIOR_UNIQUE THEN
  SIMP_TAC[OPEN_HALFSPACE_LT; SUBSET; IN_ELIM_THM; REAL_LT_IMP_LE] THEN
  X_GEN_TAC `s:real^N->bool` THEN STRIP_TAC THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN ASM_SIMP_TAC[REAL_LT_LE] THEN
  DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_CONTAINS_CBALL]) THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[SUBSET; IN_CBALL] THEN
  DISCH_THEN(MP_TAC o SPEC `x + e / norm(a) % a:real^N`) THEN
  REWRITE_TAC[NORM_ARITH `dist(x:real^N,x + y) = norm y`] THEN
  ASM_SIMP_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM; REAL_DIV_RMUL;
               NORM_EQ_0; REAL_ARITH `&0 < x ==> abs x <= x`] THEN
  DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC  `x + e / norm(a) % a:real^N`) THEN
  ASM_REWRITE_TAC[DOT_RADD; DOT_RMUL] THEN
  MATCH_MP_TAC(REAL_ARITH `&0 < e ==> ~(b + e <= b)`) THEN
  ASM_SIMP_TAC[REAL_LT_MUL; REAL_LT_DIV; NORM_POS_LT; DOT_POS_LT]);;


let INTERIOR_HALFSPACE_GE = 
prove
 (`!a:real^N b.
        ~(a = vec 0) ==> interior {x | a dot x >= b} = {x | a dot x > b}`,

  REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[REAL_ARITH `a >= b <=> --a <= --b`;
                   REAL_ARITH `a > b <=> --a < --b`] THEN
  ASM_SIMP_TAC[GSYM DOT_LNEG; INTERIOR_HALFSPACE_LE; VECTOR_NEG_EQ_0]);;


let INTERIOR_HALFSPACE_COMPONENT_LE = 
prove
 (`!a k. interior {x:real^N | x$k <= a} = {x | x$k < a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] INTERIOR_HALFSPACE_LE) THEN
  ASM_SIMP_TAC[DOT_BASIS; BASIS_NONZERO]);;


let INTERIOR_HALFSPACE_COMPONENT_GE = 
prove
 (`!a k. interior {x:real^N | x$k >= a} = {x | x$k > a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] INTERIOR_HALFSPACE_GE) THEN
  ASM_SIMP_TAC[DOT_BASIS; BASIS_NONZERO]);;


let CLOSURE_HALFSPACE_LT = 
prove
 (`!a:real^N b.
        ~(a = vec 0) ==> closure {x | a dot x < b} = {x | a dot x <= b}`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CLOSURE_INTERIOR] THEN
  REWRITE_TAC[SET_RULE `UNIV DIFF {x | P x} = {x | ~P x}`] THEN
  ASM_SIMP_TAC[REAL_ARITH `~(x < b) <=> x >= b`; INTERIOR_HALFSPACE_GE] THEN
  REWRITE_TAC[EXTENSION; IN_DIFF; IN_UNIV; IN_ELIM_THM] THEN REAL_ARITH_TAC);;


let CLOSURE_HALFSPACE_GT = 
prove
 (`!a:real^N b.
        ~(a = vec 0) ==> closure {x | a dot x > b} = {x | a dot x >= b}`,

  REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[REAL_ARITH `a >= b <=> --a <= --b`;
                   REAL_ARITH `a > b <=> --a < --b`] THEN
  ASM_SIMP_TAC[GSYM DOT_LNEG; CLOSURE_HALFSPACE_LT; VECTOR_NEG_EQ_0]);;


let CLOSURE_HALFSPACE_COMPONENT_LT = 
prove
 (`!a k. closure {x:real^N | x$k < a} = {x | x$k <= a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] CLOSURE_HALFSPACE_LT) THEN
  ASM_SIMP_TAC[DOT_BASIS; BASIS_NONZERO]);;


let CLOSURE_HALFSPACE_COMPONENT_GT = 
prove
 (`!a k. closure {x:real^N | x$k > a} = {x | x$k >= a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] CLOSURE_HALFSPACE_GT) THEN
  ASM_SIMP_TAC[DOT_BASIS; BASIS_NONZERO]);;


let INTERIOR_HYPERPLANE = 
prove
 (`!a b. ~(a = vec 0) ==> interior {x | a dot x = b} = {}`,

  REWRITE_TAC[REAL_ARITH `x = y <=> x <= y /\ x >= y`] THEN
  REWRITE_TAC[SET_RULE `{x | p x /\ q x} = {x | p x} INTER {x | q x}`] THEN
  REWRITE_TAC[INTERIOR_INTER] THEN
  ASM_SIMP_TAC[INTERIOR_HALFSPACE_LE; INTERIOR_HALFSPACE_GE] THEN
  REWRITE_TAC[EXTENSION; IN_INTER; IN_ELIM_THM; NOT_IN_EMPTY] THEN
  REAL_ARITH_TAC);;


let FRONTIER_HALFSPACE_LE = 
prove
 (`!a:real^N b. ~(a = vec 0 /\ b = &0)
                ==> frontier {x | a dot x <= b} = {x | a dot x = b}`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `a:real^N = vec 0` THEN
  ASM_SIMP_TAC[DOT_LZERO] THENL
   [ASM_CASES_TAC `&0 <= b` THEN
    ASM_REWRITE_TAC[UNIV_GSPEC; FRONTIER_UNIV; EMPTY_GSPEC; FRONTIER_EMPTY];
    ASM_SIMP_TAC[frontier; INTERIOR_HALFSPACE_LE; CLOSURE_CLOSED;
                 CLOSED_HALFSPACE_LE] THEN
    REWRITE_TAC[EXTENSION; IN_DIFF; IN_ELIM_THM] THEN REAL_ARITH_TAC]);;


let FRONTIER_HALFSPACE_GE = 
prove
 (`!a:real^N b. ~(a = vec 0 /\ b = &0)
                ==> frontier {x | a dot x >= b} = {x | a dot x = b}`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`--a:real^N`; `--b:real`] FRONTIER_HALFSPACE_LE) THEN
  ASM_REWRITE_TAC[VECTOR_NEG_EQ_0; REAL_NEG_EQ_0; DOT_LNEG] THEN
  REWRITE_TAC[REAL_LE_NEG2; REAL_EQ_NEG2; real_ge]);;


let FRONTIER_HALFSPACE_LT = 
prove
 (`!a:real^N b. ~(a = vec 0 /\ b = &0)
                ==> frontier {x | a dot x < b} = {x | a dot x = b}`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `a:real^N = vec 0` THEN
  ASM_SIMP_TAC[DOT_LZERO] THENL
   [ASM_CASES_TAC `&0 < b` THEN
    ASM_REWRITE_TAC[UNIV_GSPEC; FRONTIER_UNIV; EMPTY_GSPEC; FRONTIER_EMPTY];
    ASM_SIMP_TAC[frontier; CLOSURE_HALFSPACE_LT; INTERIOR_OPEN;
                 OPEN_HALFSPACE_LT] THEN
    REWRITE_TAC[EXTENSION; IN_DIFF; IN_ELIM_THM] THEN REAL_ARITH_TAC]);;


let FRONTIER_HALFSPACE_GT = 
prove
 (`!a:real^N b. ~(a = vec 0 /\ b = &0)
                ==> frontier {x | a dot x > b} = {x | a dot x = b}`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`--a:real^N`; `--b:real`] FRONTIER_HALFSPACE_LT) THEN
  ASM_REWRITE_TAC[VECTOR_NEG_EQ_0; REAL_NEG_EQ_0; DOT_LNEG] THEN
  REWRITE_TAC[REAL_LT_NEG2; REAL_EQ_NEG2; real_gt]);;


let INTERIOR_STANDARD_HYPERPLANE = 
prove
 (`!k a. interior {x:real^N | x$k = a} = {}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !x:real^N. x$k = x$i`
  CHOOSE_TAC THENL
   [ASM_REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  MP_TAC(ISPECL [`basis i:real^N`; `a:real`] INTERIOR_HYPERPLANE) THEN
  ASM_SIMP_TAC[DOT_BASIS; BASIS_NONZERO]);;


let EMPTY_INTERIOR_LOWDIM = 
prove
 (`!s:real^N->bool. dim(s) < dimindex(:N) ==> interior s = {}`,

  GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP LOWDIM_SUBSET_HYPERPLANE) THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^N` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC(SET_RULE
   `!t u. s SUBSET t /\ t SUBSET u /\ u = {} ==> s = {}`) THEN
  MAP_EVERY EXISTS_TAC
   [`interior(span(s):real^N->bool)`;
    `interior({x:real^N | a dot x = &0})`] THEN
  ASM_SIMP_TAC[SUBSET_INTERIOR; SPAN_INC; INTERIOR_HYPERPLANE]);;

(* ------------------------------------------------------------------------- *)
(* Unboundedness of halfspaces.                                              *)
(* ------------------------------------------------------------------------- *)


let UNBOUNDED_HALFSPACE_COMPONENT_LE = 
prove
 (`!a k. ~bounded {x:real^N | x$k <= a}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `?i. 1 <= i /\ i <= dimindex(:N) /\ !z:real^N. z$k = z$i`
  CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
  ASM_REWRITE_TAC[bounded; FORALL_IN_GSPEC] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` MP_TAC) THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP] THEN
  EXISTS_TAC `--(&1 + max (abs B) (abs a)) % basis i:real^N` THEN
  ASM_SIMP_TAC[NORM_MUL; NORM_BASIS; BASIS_COMPONENT;
               VECTOR_MUL_COMPONENT] THEN
  REAL_ARITH_TAC);;


let UNBOUNDED_HALFSPACE_COMPONENT_GE = 
prove
 (`!a k. ~bounded {x:real^N | x$k >= a}`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP BOUNDED_NEGATIONS) THEN
  MP_TAC(SPECL [`--a:real`; `k:num`] UNBOUNDED_HALFSPACE_COMPONENT_LE) THEN
  REWRITE_TAC[CONTRAPOS_THM] THEN MATCH_MP_TAC EQ_IMP THEN
  AP_TERM_TAC THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN CONJ_TAC THENL
   [MESON_TAC[VECTOR_NEG_NEG];
    REWRITE_TAC[IN_ELIM_THM; VECTOR_NEG_COMPONENT] THEN REAL_ARITH_TAC]);;


let UNBOUNDED_HALFSPACE_COMPONENT_LT = 
prove
 (`!a k. ~bounded {x:real^N | x$k < a}`,


let UNBOUNDED_HALFSPACE_COMPONENT_GT = 
prove
 (`!a k. ~bounded {x:real^N | x$k > a}`,


let BOUNDED_HALFSPACE_LE = 
prove
 (`!a:real^N b. bounded {x | a dot x <= b} <=> a = vec 0 /\ b < &0`,

  GEOM_BASIS_MULTIPLE_TAC 1 `a:real^N` THEN
  SIMP_TAC[DOT_LMUL; DOT_BASIS; VECTOR_MUL_EQ_0; DIMINDEX_GE_1; LE_REFL;
           BASIS_NONZERO] THEN
  X_GEN_TAC `a:real` THEN ASM_CASES_TAC `a = &0` THEN ASM_REWRITE_TAC[] THEN
  DISCH_TAC THEN X_GEN_TAC `b:real` THENL
   [REWRITE_TAC[REAL_MUL_LZERO; DOT_LZERO; GSYM REAL_NOT_LE] THEN
    ASM_CASES_TAC `&0 <= b` THEN
    ASM_REWRITE_TAC[BOUNDED_EMPTY; NOT_BOUNDED_UNIV;
                    SET_RULE `{x | T} = UNIV`; EMPTY_GSPEC];
    ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
    ASM_SIMP_TAC[GSYM REAL_LE_RDIV_EQ; REAL_LT_LE;
                 UNBOUNDED_HALFSPACE_COMPONENT_LE]]);;


let BOUNDED_HALFSPACE_GE = 
prove
 (`!a:real^N b. bounded {x | a dot x >= b} <=> a = vec 0 /\ &0 < b`,

  REWRITE_TAC[REAL_ARITH `a >= b <=> --a <= --b`] THEN
  REWRITE_TAC[GSYM DOT_LNEG; BOUNDED_HALFSPACE_LE] THEN
  REWRITE_TAC[VECTOR_NEG_EQ_0; REAL_ARITH `--b < &0 <=> &0 < b`]);;


let BOUNDED_HALFSPACE_LT = 
prove
 (`!a:real^N b. bounded {x | a dot x < b} <=> a = vec 0 /\ b <= &0`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `a:real^N = vec 0` THEN
  ASM_REWRITE_TAC[] THENL
   [REWRITE_TAC[DOT_LZERO; GSYM REAL_NOT_LE] THEN ASM_CASES_TAC `b <= &0` THEN
    ASM_REWRITE_TAC[BOUNDED_EMPTY; NOT_BOUNDED_UNIV;
                    SET_RULE `{x | T} = UNIV`; EMPTY_GSPEC];
    ONCE_REWRITE_TAC[GSYM BOUNDED_CLOSURE_EQ] THEN
    ASM_SIMP_TAC[CLOSURE_HALFSPACE_LT; BOUNDED_HALFSPACE_LE]]);;


let BOUNDED_HALFSPACE_GT = 
prove
 (`!a:real^N b. bounded {x | a dot x > b} <=> a = vec 0 /\ &0 <= b`,

  REWRITE_TAC[REAL_ARITH `a > b <=> --a < --b`] THEN
  REWRITE_TAC[GSYM DOT_LNEG; BOUNDED_HALFSPACE_LT] THEN
  REWRITE_TAC[VECTOR_NEG_EQ_0; REAL_ARITH `--b <= &0 <=> &0 <= b`]);;

(* ------------------------------------------------------------------------- *)
(* Equality of continuous functions on closure and related results.          *)
(* ------------------------------------------------------------------------- *)


let FORALL_IN_CLOSURE = 
prove
 (`!f:real^M->real^N s t.
        closed t /\ f continuous_on (closure s) /\
        (!x. x IN s ==> f x IN t)
        ==> (!x. x IN closure s ==> f x IN t)`,

  REWRITE_TAC[SET_RULE `(!x. x IN s ==> f x IN t) <=>
                        s SUBSET {x | x IN s /\ f x IN t}`] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSURE_MINIMAL THEN
  ASM_REWRITE_TAC[CLOSED_CLOSURE] THEN CONJ_TAC THENL
   [MP_TAC(ISPEC `s:real^M->bool` CLOSURE_SUBSET) THEN ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE THEN
    ASM_REWRITE_TAC[CLOSED_CLOSURE]]);;


let FORALL_IN_CLOSURE_EQ = 
prove
 (`!f s t.
         closed t /\ f continuous_on closure s
         ==> ((!x. x IN closure s ==> f x IN t) <=>
              (!x. x IN s ==> f x IN t))`,


let SUP_CLOSURE = 
prove
 (`!s. sup(IMAGE drop (closure s)) = sup(IMAGE drop s)`,

  GEN_TAC THEN MATCH_MP_TAC SUP_EQ THEN
  REWRITE_TAC[FORALL_IN_IMAGE] THEN GEN_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `drop x <= b <=> x IN {x | drop x <= b}`] THEN
  MATCH_MP_TAC FORALL_IN_CLOSURE_EQ THEN
  REWRITE_TAC[CONTINUOUS_ON_ID; drop; CLOSED_HALFSPACE_COMPONENT_LE]);;


let INF_CLOSURE = 
prove
 (`!s. inf(IMAGE drop (closure s)) = inf(IMAGE drop s)`,

  GEN_TAC THEN MATCH_MP_TAC INF_EQ THEN
  REWRITE_TAC[FORALL_IN_IMAGE] THEN GEN_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `b <= drop x <=> x IN {x | b <= drop x}`] THEN
  MATCH_MP_TAC FORALL_IN_CLOSURE_EQ THEN
  REWRITE_TAC[CONTINUOUS_ON_ID; drop; CLOSED_HALFSPACE_COMPONENT_GE;
              GSYM real_ge]);;


let CONTINUOUS_LE_ON_CLOSURE = 
prove
 (`!f:real^M->real s a.
        (lift o f) continuous_on closure(s) /\ (!x. x IN s ==> f(x) <= a)
        ==> !x. x IN closure(s) ==> f(x) <= a`,

  
let lemma = prove
   (`x IN s ==> f x <= a <=> x IN s ==> (lift o f) x IN {y | y$1 <= a}`,
    REWRITE_TAC[IN_ELIM_THM; o_THM; GSYM drop; LIFT_DROP]) in
  REWRITE_TAC[lemma] THEN REPEAT GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC FORALL_IN_CLOSURE THEN
  ASM_REWRITE_TAC[ETA_AX; CLOSED_HALFSPACE_COMPONENT_LE]);;


let CONTINUOUS_GE_ON_CLOSURE = 
prove
 (`!f:real^M->real s a.
        (lift o f) continuous_on closure(s) /\ (!x. x IN s ==> a <= f(x))
        ==> !x. x IN closure(s) ==> a <= f(x)`,

  
let lemma = prove
   (`x IN s ==> a <= f x <=> x IN s ==> (lift o f) x IN {y | y$1 >= a}`,
    REWRITE_TAC[IN_ELIM_THM; o_THM; GSYM drop; real_ge; LIFT_DROP]) in
  REWRITE_TAC[lemma] THEN REPEAT GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC FORALL_IN_CLOSURE THEN
  ASM_REWRITE_TAC[ETA_AX; CLOSED_HALFSPACE_COMPONENT_GE]);;


let CONTINUOUS_CONSTANT_ON_CLOSURE = 
prove
 (`!f:real^M->real^N s a.
        f continuous_on closure(s) /\ (!x. x IN s ==> f(x) = a)
        ==> !x. x IN closure(s) ==> f(x) = a`,

  REWRITE_TAC[SET_RULE
   `x IN s ==> f x = a <=> x IN s ==> f x IN {a}`] THEN
  REPEAT GEN_TAC THEN STRIP_TAC THEN MATCH_MP_TAC FORALL_IN_CLOSURE THEN
  ASM_REWRITE_TAC[CLOSED_SING]);;


let CONTINUOUS_AGREE_ON_CLOSURE = 
prove
 (`!g h:real^M->real^N.
        g continuous_on closure s /\ h continuous_on closure s /\
        (!x. x IN s ==> g x = h x)
        ==> !x. x IN closure s ==> g x = h x`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[GSYM VECTOR_SUB_EQ] THEN STRIP_TAC THEN
  MATCH_MP_TAC CONTINUOUS_CONSTANT_ON_CLOSURE THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_SUB]);;


let CONTINUOUS_CLOSED_IN_PREIMAGE_CONSTANT = 
prove
 (`!f:real^M->real^N s a.
        f continuous_on s
        ==> closed_in (subtopology euclidean s) {x | x IN s /\ f x = a}`,

  REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE
   `{x | x IN s /\ f(x) = a} = {x | x IN s /\ f(x) IN {a}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE THEN
  ASM_REWRITE_TAC[CLOSED_SING]);;


let CONTINUOUS_CLOSED_PREIMAGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
      f continuous_on s /\ closed s ==> closed {x | x IN s /\ f(x) = a}`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `{x | x IN s /\ (f:real^M->real^N)(x) = a} = {}` THEN
  ASM_REWRITE_TAC[CLOSED_EMPTY] THEN ONCE_REWRITE_TAC[SET_RULE
   `{x | x IN s /\ f(x) = a} = {x | x IN s /\ f(x) IN {a}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE THEN
  ASM_REWRITE_TAC[CLOSED_SING] THEN ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Theorems relating continuity and uniform continuity to closures.          *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_ON_CLOSURE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on closure s <=>
        !x e. x IN closure s /\ &0 < e
              ==> ?d. &0 < d /\
                      !y. y IN s /\ dist(y,x) < d ==> dist(f y,f x) < e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_on] THEN
  EQ_TAC THENL [MESON_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET]; ALL_TAC] THEN
  DISCH_TAC THEN X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o SPECL [`x:real^M`; `e / &2`]) THEN
  ANTS_TAC THENL [ASM_REWRITE_TAC[REAL_HALF]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `d / &2` THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  X_GEN_TAC `y:real^M` THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`y:real^M`; `e / &2`]) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real` STRIP_ASSUME_TAC) THEN
  MP_TAC(ISPECL [`y:real^M`; `s:real^M->bool`] CLOSURE_APPROACHABLE) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(MP_TAC o SPEC `min k (d / &2)`) THEN
  ASM_REWRITE_TAC[REAL_HALF; REAL_LT_MIN] THEN
  ASM_MESON_TAC[DIST_SYM; NORM_ARITH
    `dist(a,b) < e / &2 /\ dist(b,c) < e / &2 ==> dist(a,c) < e`]);;


let CONTINUOUS_ON_CLOSURE_SEQUENTIALLY = 
prove
 (`!f:real^M->real^N s.
        f continuous_on closure s <=>
        !x a. a IN closure s /\ (!n. x n IN s) /\ (x --> a) sequentially
              ==> ((f o x) --> f a) sequentially`,

  REWRITE_TAC[CONTINUOUS_ON_CLOSURE] THEN
  REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN
  REWRITE_TAC[IMP_IMP; GSYM continuous_within] THEN
  REWRITE_TAC[CONTINUOUS_WITHIN_SEQUENTIALLY] THEN MESON_TAC[]);;


let UNIFORMLY_CONTINUOUS_ON_CLOSURE = 
prove
 (`!f:real^M->real^N s.
        f uniformly_continuous_on s /\ f continuous_on closure s
        ==> f uniformly_continuous_on closure s`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[uniformly_continuous_on] THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &3`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `d / &3` THEN CONJ_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^M`] THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [continuous_on]) THEN
  DISCH_THEN(fun th ->
    MP_TAC(SPEC `y:real^M` th) THEN MP_TAC(SPEC `x:real^M` th)) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o SPEC `e / &3`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d1:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  MP_TAC(ISPECL [`x:real^M`; `s:real^M->bool`] CLOSURE_APPROACHABLE) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(MP_TAC o SPEC `min d1 (d / &3)`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; REWRITE_TAC[REAL_LT_MIN]] THEN
  DISCH_THEN(X_CHOOSE_THEN `x':real^M` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(MP_TAC o SPEC `x':real^M`) THEN
  ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET] THEN DISCH_TAC THEN
  DISCH_THEN(MP_TAC o SPEC `e / &3`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d2:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  MP_TAC(ISPECL [`y:real^M`; `s:real^M->bool`] CLOSURE_APPROACHABLE) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(MP_TAC o SPEC `min d2 (d / &3)`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; REWRITE_TAC[REAL_LT_MIN]] THEN
  DISCH_THEN(X_CHOOSE_THEN `y':real^M` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(MP_TAC o SPEC `y':real^M`) THEN
  ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`x':real^M`; `y':real^M`]) THEN
  ASM_MESON_TAC[DIST_SYM; NORM_ARITH
   `dist(y,x) < d / &3 /\ dist(x',x) < d / &3 /\ dist(y',y) < d / &3
    ==> dist(y',x') < d`]);;

(* ------------------------------------------------------------------------- *)
(* Continuity properties for square roots. We get other forms of this        *)
(* later (transcendentals.ml and realanalysis.ml) but it's nice to have      *)
(* them around earlier.                                                      *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_AT_SQRT = 
prove
 (`!a s. &0 < drop a ==>  (lift o sqrt o drop) continuous (at a)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[continuous_at; o_THM; DIST_LIFT] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  EXISTS_TAC `min (drop a) (e * sqrt(drop a))` THEN
  ASM_SIMP_TAC[REAL_LT_MIN; SQRT_POS_LT; REAL_LT_MUL; DIST_REAL] THEN
  X_GEN_TAC `b:real^1` THEN REWRITE_TAC[GSYM drop] THEN STRIP_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP (REAL_ARITH
   `abs(b - a) < a ==> &0 < b`)) THEN
  SUBGOAL_THEN
   `sqrt(drop b) - sqrt(drop a) =
    (drop b - drop a) / (sqrt(drop a) + sqrt(drop b))`
  SUBST1_TAC THENL
   [MATCH_MP_TAC(REAL_FIELD
     `sa pow 2 = a /\ sb pow 2 = b /\ &0 < sa /\ &0 < sb
      ==> sb - sa = (b - a) / (sa + sb)`) THEN
    ASM_SIMP_TAC[SQRT_POS_LT; SQRT_POW_2; REAL_LT_IMP_LE];
    ASM_SIMP_TAC[REAL_ABS_DIV; SQRT_POS_LT; REAL_LT_ADD; REAL_LT_LDIV_EQ;
                 REAL_ARITH `&0 < x ==> abs x = x`] THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        REAL_LTE_TRANS)) THEN
    ASM_SIMP_TAC[REAL_LE_LMUL_EQ; REAL_LE_ADDR; SQRT_POS_LE;
                 REAL_LT_IMP_LE]]);;


let CONTINUOUS_WITHIN_LIFT_SQRT = 
prove
 (`!a s. (!x. x IN s ==> &0 <= drop x)
         ==> (lift o sqrt o drop) continuous (at a within s)`,

  REPEAT STRIP_TAC THEN
  REPEAT_TCL DISJ_CASES_THEN ASSUME_TAC
   (REAL_ARITH `drop a < &0 \/ drop a = &0 \/ &0 < drop a`)
  THENL
   [MATCH_MP_TAC CONTINUOUS_WITHIN_SUBSET THEN
    EXISTS_TAC `{x | &0 <= drop x}` THEN
    ASM_SIMP_TAC[SUBSET; IN_ELIM_THM] THEN
    MATCH_MP_TAC CONTINUOUS_WITHIN_CLOSED_NONTRIVIAL THEN
    ASM_REWRITE_TAC[IN_ELIM_THM; REAL_NOT_LE] THEN
    REWRITE_TAC[drop; REWRITE_RULE[real_ge] CLOSED_HALFSPACE_COMPONENT_GE];
    RULE_ASSUM_TAC(REWRITE_RULE[GSYM LIFT_EQ; LIFT_DROP; LIFT_NUM]) THEN
    ASM_REWRITE_TAC[continuous_within; o_THM; DROP_VEC; SQRT_0; LIFT_NUM] THEN
    REWRITE_TAC[DIST_0; NORM_LIFT; NORM_REAL; GSYM drop] THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    EXISTS_TAC `(e:real) pow 2` THEN ASM_SIMP_TAC[REAL_POW_LT] THEN
    X_GEN_TAC `x:real^1` THEN STRIP_TAC THEN
    ASM_SIMP_TAC[real_abs; SQRT_POS_LE] THEN
    SUBGOAL_THEN `e = sqrt(e pow 2)` SUBST1_TAC THENL
     [ASM_SIMP_TAC[POW_2_SQRT; REAL_LT_IMP_LE];
      MATCH_MP_TAC SQRT_MONO_LT THEN ASM_SIMP_TAC[] THEN ASM_REAL_ARITH_TAC];
    MATCH_MP_TAC CONTINUOUS_AT_WITHIN THEN
    MATCH_MP_TAC CONTINUOUS_AT_SQRT THEN ASM_REWRITE_TAC[]]);;


let CONTINUOUS_WITHIN_SQRT_COMPOSE = 
prove
 (`!f s a:real^N.
        (\x. lift(f x)) continuous (at a within s) /\
        (&0 < f a \/ !x. x IN s ==> &0 <= f x)
        ==> (\x. lift(sqrt(f x))) continuous (at a within s)`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN
   `(\x:real^N. lift(sqrt(f x))) = (lift o sqrt o drop) o (lift o f)`
  SUBST1_TAC THENL [REWRITE_TAC[o_DEF; LIFT_DROP]; ALL_TAC] THEN
  REPEAT STRIP_TAC THEN
  (MATCH_MP_TAC CONTINUOUS_WITHIN_COMPOSE THEN
   CONJ_TAC THENL [ASM_REWRITE_TAC[o_DEF]; ALL_TAC])
  THENL
   [MATCH_MP_TAC CONTINUOUS_AT_WITHIN THEN
    MATCH_MP_TAC CONTINUOUS_AT_SQRT THEN ASM_REWRITE_TAC[o_DEF; LIFT_DROP];
    MATCH_MP_TAC CONTINUOUS_WITHIN_LIFT_SQRT THEN
    ASM_REWRITE_TAC[FORALL_IN_IMAGE; o_DEF; LIFT_DROP]]);;


let CONTINUOUS_AT_SQRT_COMPOSE = 
prove
 (`!f a:real^N.
        (\x. lift(f x)) continuous (at a) /\ (&0 < f a \/ !x. &0 <= f x)
        ==> (\x. lift(sqrt(f x))) continuous (at a)`,

  REPEAT GEN_TAC THEN
  MP_TAC(ISPECL [`f:real^N->real`; `(:real^N)`; `a:real^N`]
        CONTINUOUS_WITHIN_SQRT_COMPOSE) THEN
  REWRITE_TAC[WITHIN_UNIV; IN_UNIV]);;


let CONTINUOUS_ON_LIFT_SQRT = 
prove
 (`!s. (!x. x IN s ==> &0 <= drop x)
       ==> (lift o sqrt o drop) continuous_on s`,


let CONTINUOUS_ON_LIFT_SQRT_COMPOSE = 
prove
 (`!f:real^N->real s.
        (lift o f) continuous_on s /\ (!x. x IN s ==> &0 <= f x)
        ==> (\x. lift(sqrt(f x))) continuous_on s`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `(\x:real^N. lift(sqrt(f x))) = (lift o sqrt o drop) o (lift o f)`
  SUBST1_TAC THENL
   [REWRITE_TAC[o_DEF; LIFT_DROP];
    MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC CONTINUOUS_ON_LIFT_SQRT THEN
    ASM_REWRITE_TAC[FORALL_IN_IMAGE; o_THM; LIFT_DROP]]);;

(* ------------------------------------------------------------------------- *)
(* Cauchy continuity, and the extension of functions to closures.            *)
(* ------------------------------------------------------------------------- *)


let UNIFORMLY_CONTINUOUS_IMP_CAUCHY_CONTINUOUS = 
prove
 (`!f:real^M->real^N s.
        f uniformly_continuous_on s
        ==> (!x. cauchy x /\ (!n. (x n) IN s) ==> cauchy(f o x))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[uniformly_continuous_on; cauchy; o_DEF] THEN
  MESON_TAC[]);;


let CONTINUOUS_CLOSED_IMP_CAUCHY_CONTINUOUS = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s /\ closed s
        ==> (!x. cauchy x /\ (!n. (x n) IN s) ==> cauchy(f o x))`,

  REWRITE_TAC[GSYM COMPLETE_EQ_CLOSED; CONTINUOUS_ON_SEQUENTIALLY] THEN
  REWRITE_TAC[complete] THEN MESON_TAC[CONVERGENT_IMP_CAUCHY]);;


let CAUCHY_CONTINUOUS_UNIQUENESS_LEMMA = 
prove
 (`!f:real^M->real^N s.
        (!x. cauchy x /\ (!n. (x n) IN s) ==> cauchy(f o x))
        ==> !a x. (!n. (x n) IN s) /\ (x --> a) sequentially
                  ==> ?l. ((f o x) --> l) sequentially /\
                          !y. (!n. (y n) IN s) /\ (y --> a) sequentially
                              ==> ((f o y) --> l) sequentially`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `x:num->real^M`) THEN
  ANTS_TAC THENL [ASM_MESON_TAC[CONVERGENT_IMP_CAUCHY]; ALL_TAC] THEN
  REWRITE_TAC[GSYM CONVERGENT_EQ_CAUCHY] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `l:real^N` THEN DISCH_TAC THEN ASM_REWRITE_TAC[] THEN
  X_GEN_TAC `y:num->real^M` THEN STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o SPEC `y:num->real^M`) THEN
  ANTS_TAC THENL [ASM_MESON_TAC[CONVERGENT_IMP_CAUCHY]; ALL_TAC] THEN
  REWRITE_TAC[GSYM CONVERGENT_EQ_CAUCHY] THEN
  DISCH_THEN(X_CHOOSE_THEN `m:real^N` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `l:real^N = m` (fun th -> ASM_REWRITE_TAC[th]) THEN
  ONCE_REWRITE_TAC[GSYM VECTOR_SUB_EQ] THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_UNIQUE) THEN
  EXISTS_TAC `\n:num. (f:real^M->real^N)(x n) - f(y n)` THEN
  RULE_ASSUM_TAC(REWRITE_RULE[o_DEF]) THEN
  ASM_SIMP_TAC[LIM_SUB; TRIVIAL_LIMIT_SEQUENTIALLY] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC
   `\n. if EVEN n then x(n DIV 2):real^M else y(n DIV 2)`) THEN
  REWRITE_TAC[cauchy; o_THM; LIM_SEQUENTIALLY] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN MAP_EVERY UNDISCH_TAC
     [`((y:num->real^M) --> a) sequentially`;
      `((x:num->real^M) --> a) sequentially`] THEN
    REPEAT(FIRST_X_ASSUM(K ALL_TAC o check (is_forall o concl))) THEN
    REWRITE_TAC[LIM_SEQUENTIALLY] THEN
    DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
    DISCH_THEN(X_CHOOSE_TAC `N1:num`) THEN
    DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
    DISCH_THEN(X_CHOOSE_TAC `N2:num`) THEN
    EXISTS_TAC `2 * (N1 + N2)` THEN
    MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN STRIP_TAC THEN
    REPEAT(FIRST_X_ASSUM(fun th ->
      MP_TAC(SPEC `m DIV 2` th) THEN MP_TAC(SPEC `n DIV 2` th))) THEN
    REPEAT(ANTS_TAC THENL [ASM_ARITH_TAC; DISCH_TAC]) THEN
    REPEAT(COND_CASES_TAC THEN ASM_REWRITE_TAC[]) THEN
    REPEAT(FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM REAL_NOT_LE])) THEN
    CONV_TAC NORM_ARITH;
    MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
    ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN DISCH_TAC THEN
    X_GEN_TAC `n:num` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPECL [`2 * n`; `2 * n + 1`]) THEN
    ANTS_TAC THENL [ASM_ARITH_TAC; ALL_TAC] THEN
    REWRITE_TAC[EVEN_ADD; EVEN_MULT; ARITH_EVEN] THEN
    REWRITE_TAC[ARITH_RULE `(2 * n) DIV 2 = n /\ (2 * n + 1) DIV 2 = n`] THEN
    REWRITE_TAC[dist; VECTOR_SUB_RZERO]]);;


let CAUCHY_CONTINUOUS_EXTENDS_TO_CLOSURE = 
prove
 (`!f:real^M->real^N s.
        (!x. cauchy x /\ (!n. (x n) IN s) ==> cauchy(f o x))
        ==> ?g. g continuous_on closure s /\ (!x. x IN s ==> g x = f x)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `!a:real^M. ?x.
       a IN closure s ==> (!n. x n IN s) /\ (x --> a) sequentially`
  MP_TAC THENL [MESON_TAC[CLOSURE_SEQUENTIAL]; ALL_TAC] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `X:real^M->num->real^M` THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CAUCHY_CONTINUOUS_UNIQUENESS_LEMMA) THEN
  DISCH_THEN(MP_TAC o GEN `a:real^M` o
   SPECL [`a:real^M`; `(X:real^M->num->real^M) a`]) THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (MESON[]
   `(!a. P a ==> Q a) ==> ((!a. P a ==> R a) ==> p)
    ==> ((!a. Q a ==> R a) ==> p)`)) THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^M->real^N` THEN
  STRIP_TAC THEN
  MATCH_MP_TAC(TAUT `b /\ (b ==> a) ==> a /\ b`) THEN CONJ_TAC THENL
   [X_GEN_TAC `a:real^M` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `a:real^M`) THEN
    ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET] THEN
    DISCH_THEN(MP_TAC o SPEC `(\n. a):num->real^M` o CONJUNCT2) THEN
    ASM_SIMP_TAC[LIM_CONST_EQ; o_DEF; TRIVIAL_LIMIT_SEQUENTIALLY];
    STRIP_TAC] THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_CLOSURE_SEQUENTIALLY] THEN
  MAP_EVERY X_GEN_TAC [`x:num->real^M`; `a:real^M`] THEN STRIP_TAC THEN
  MATCH_MP_TAC LIM_TRANSFORM_EVENTUALLY THEN
  EXISTS_TAC `(f:real^M->real^N) o (x:num->real^M)` THEN ASM_SIMP_TAC[] THEN
  MATCH_MP_TAC ALWAYS_EVENTUALLY THEN ASM_SIMP_TAC[o_THM]);;


let UNIFORMLY_CONTINUOUS_EXTENDS_TO_CLOSURE = 
prove
 (`!f:real^M->real^N s.
   f uniformly_continuous_on s
   ==> ?g. g uniformly_continuous_on closure s /\ (!x. x IN s ==> g x = f x) /\
           !h. h continuous_on closure s /\ (!x. x IN s ==> h x = f x)
               ==> !x. x IN closure s ==> h x = g x`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CAUCHY_CONTINUOUS_EXTENDS_TO_CLOSURE o
   MATCH_MP UNIFORMLY_CONTINUOUS_IMP_CAUCHY_CONTINUOUS) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^M->real^N` THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[UNIFORMLY_CONTINUOUS_ON_CLOSURE; UNIFORMLY_CONTINUOUS_ON_EQ];
    ASM_MESON_TAC[CONTINUOUS_AGREE_ON_CLOSURE]]);;


let CAUCHY_CONTINUOUS_IMP_CONTINUOUS = 
prove
 (`!f:real^M->real^N s.
        (!x. cauchy x /\ (!n. (x n) IN s) ==> cauchy(f o x))
        ==> f continuous_on s`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(CHOOSE_TAC o MATCH_MP CAUCHY_CONTINUOUS_EXTENDS_TO_CLOSURE) THEN
  ASM_MESON_TAC[CONTINUOUS_ON_SUBSET; CLOSURE_SUBSET; CONTINUOUS_ON_EQ]);;


let BOUNDED_UNIFORMLY_CONTINUOUS_IMAGE = 
prove
 (`!f:real^M->real^N s.
        f uniformly_continuous_on s /\ bounded s ==> bounded(IMAGE f s)`,

  REPEAT STRIP_TAC THEN FIRST_ASSUM
   (MP_TAC o MATCH_MP UNIFORMLY_CONTINUOUS_EXTENDS_TO_CLOSURE) THEN
  DISCH_THEN(X_CHOOSE_THEN `g:real^M->real^N` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC BOUNDED_SUBSET THEN
  EXISTS_TAC `IMAGE (g:real^M->real^N) (closure s)` THEN CONJ_TAC THENL
   [ASM_MESON_TAC[COMPACT_CLOSURE; UNIFORMLY_CONTINUOUS_IMP_CONTINUOUS;
                  COMPACT_IMP_BOUNDED; COMPACT_CONTINUOUS_IMAGE];
    MP_TAC(ISPEC `s:real^M->bool` CLOSURE_SUBSET) THEN ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Occasionally useful invariance properties.                                *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_AT_COMPOSE_EQ = 
prove
 (`!f:real^M->real^N g:real^M->real^M h:real^M->real^M.
        g continuous at x /\ h continuous at (g x) /\
        (!y. g(h y) = y) /\ h(g x) = x
        ==> (f continuous at (g x) <=> (\x. f(g x)) continuous at x)`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN
  ASM_SIMP_TAC[REWRITE_RULE[o_DEF] CONTINUOUS_AT_COMPOSE] THEN
  DISCH_TAC THEN
  SUBGOAL_THEN
   `((f:real^M->real^N) o (g:real^M->real^M) o (h:real^M->real^M))
     continuous at (g(x:real^M))`
  MP_TAC THENL
   [REWRITE_TAC[o_ASSOC] THEN MATCH_MP_TAC CONTINUOUS_AT_COMPOSE THEN
    ASM_REWRITE_TAC[o_DEF];

    ASM_REWRITE_TAC[o_DEF; ETA_AX]]);;


let CONTINUOUS_AT_TRANSLATION = 
prove
 (`!a z f:real^M->real^N.
      f continuous at (a + z) <=> (\x. f(a + x)) continuous at z`,

  REPEAT GEN_TAC THEN MATCH_MP_TAC CONTINUOUS_AT_COMPOSE_EQ THEN
  EXISTS_TAC `\x:real^M. x - a` THEN
  SIMP_TAC[CONTINUOUS_ADD; CONTINUOUS_SUB;
           CONTINUOUS_AT_ID; CONTINUOUS_CONST] THEN
  VECTOR_ARITH_TAC);;

add_translation_invariants [CONTINUOUS_AT_TRANSLATION];;


let CONTINUOUS_AT_LINEAR_IMAGE = 
prove
 (`!h:real^M->real^M z f:real^M->real^N.
        linear h /\ (!x. norm(h x) = norm x)
        ==> (f continuous at (h z) <=> (\x. f(h x)) continuous at z)`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o GEN_REWRITE_RULE I
   [GSYM ORTHOGONAL_TRANSFORMATION]) THEN
  FIRST_ASSUM(X_CHOOSE_TAC `g:real^M->real^M` o MATCH_MP
    ORTHOGONAL_TRANSFORMATION_INVERSE) THEN
  MATCH_MP_TAC CONTINUOUS_AT_COMPOSE_EQ THEN
  EXISTS_TAC `g:real^M->real^M` THEN
  RULE_ASSUM_TAC(REWRITE_RULE[ORTHOGONAL_TRANSFORMATION]) THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_AT]);;

add_linear_invariants [CONTINUOUS_AT_LINEAR_IMAGE];;

(* ------------------------------------------------------------------------- *)
(* Interior of an injective image.                                           *)
(* ------------------------------------------------------------------------- *)


let INTERIOR_IMAGE_SUBSET = 
prove
 (`!f:real^M->real^N s.
       (!x. f continuous at x) /\ (!x y. f x = f y ==> x = y)
       ==> interior(IMAGE f s) SUBSET IMAGE f (interior s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[SUBSET] THEN
  REWRITE_TAC[interior; IN_ELIM_THM] THEN
  X_GEN_TAC `y:real^N` THEN
  DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[IN_IMAGE; IN_ELIM_THM] THEN
  SUBGOAL_THEN `y IN IMAGE (f:real^M->real^N) s` MP_TAC THENL
   [ASM SET_TAC[]; ALL_TAC] THEN
  REWRITE_TAC[IN_IMAGE] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REPEAT STRIP_TAC THEN
  ASM_REWRITE_TAC[IN_ELIM_THM] THEN FIRST_X_ASSUM SUBST_ALL_TAC THEN
  EXISTS_TAC `{x | (f:real^M->real^N)(x) IN t}` THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN CONJ_TAC THENL
   [MATCH_MP_TAC CONTINUOUS_OPEN_PREIMAGE_UNIV THEN ASM_MESON_TAC[];
    ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Making a continuous function avoid some value in a neighbourhood.         *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_WITHIN_AVOID = 
prove
 (`!f:real^M->real^N x s a.
        f continuous (at x within s) /\ x IN s /\  ~(f x = a)
        ==> ?e. &0 < e /\ !y. y IN s /\ dist(x,y) < e ==> ~(f y = a)`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [continuous_within]) THEN
  DISCH_THEN(MP_TAC o SPEC `norm((f:real^M->real^N) x - a)`) THEN
  ASM_REWRITE_TAC[NORM_POS_LT; VECTOR_SUB_EQ] THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN MATCH_MP_TAC MONO_AND THEN
  REWRITE_TAC[] THEN MATCH_MP_TAC MONO_FORALL THEN
  GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN SIMP_TAC[] THEN NORM_ARITH_TAC);;


let CONTINUOUS_AT_AVOID = 
prove
 (`!f:real^M->real^N x a.
        f continuous (at x) /\ ~(f x = a)
        ==> ?e. &0 < e /\ !y. dist(x,y) < e ==> ~(f y = a)`,

  MP_TAC CONTINUOUS_WITHIN_AVOID THEN
  REPLICATE_TAC 2 (MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN
  DISCH_THEN(MP_TAC o SPEC `(:real^M)`) THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  REWRITE_TAC[WITHIN_UNIV; IN_UNIV]);;


let CONTINUOUS_ON_AVOID = 
prove
 (`!f:real^M->real^N x s a.
        f continuous_on s /\ x IN s /\ ~(f x = a)
        ==> ?e. &0 < e /\ !y. y IN s /\ dist(x,y) < e ==> ~(f y = a)`,

  REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_WITHIN_AVOID THEN
  ASM_SIMP_TAC[]);;


let CONTINUOUS_ON_OPEN_AVOID = 
prove
 (`!f:real^M->real^N x s a.
        f continuous_on s /\ open s /\ x IN s /\ ~(f x = a)
        ==> ?e. &0 < e /\ !y. dist(x,y) < e ==> ~(f y = a)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `open(s:real^M->bool)` THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_AT] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_AT_AVOID THEN
  ASM_SIMP_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Proving a function is constant by proving open-ness of level set.         *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_LEVELSET_OPEN_IN_CASES = 
prove
 (`!f:real^M->real^N s a.
        connected s /\
        f continuous_on s /\
        open_in (subtopology euclidean s) {x | x IN s /\ f x = a}
        ==> (!x. x IN s ==> ~(f x = a)) \/ (!x. x IN s ==> f x = a)`,

  REWRITE_TAC[SET_RULE `(!x. x IN s ==> ~(f x = a)) <=>
                        {x | x IN s /\ f x = a} = {}`;
              SET_RULE `(!x. x IN s ==> f x = a) <=>
                        {x | x IN s /\ f x = a} = s`] THEN
  REWRITE_TAC[CONNECTED_CLOPEN] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[CONTINUOUS_CLOSED_IN_PREIMAGE_CONSTANT]);;


let CONTINUOUS_LEVELSET_OPEN_IN = 
prove
 (`!f:real^M->real^N s a.
        connected s /\
        f continuous_on s /\
        open_in (subtopology euclidean s) {x | x IN s /\ f x = a} /\
        (?x. x IN s /\ f x = a)
        ==> (!x. x IN s ==> f x = a)`,


let CONTINUOUS_LEVELSET_OPEN = 
prove
 (`!f:real^M->real^N s a.
        connected s /\
        f continuous_on s /\
        open {x | x IN s /\ f x = a} /\
        (?x. x IN s /\ f x = a)
        ==> (!x. x IN s ==> f x = a)`,

  REPEAT GEN_TAC THEN DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
  MATCH_MP_TAC CONTINUOUS_LEVELSET_OPEN_IN THEN
  ASM_REWRITE_TAC[OPEN_IN_OPEN] THEN
  EXISTS_TAC `{x | x IN s /\ (f:real^M->real^N) x = a}` THEN
  ASM_REWRITE_TAC[] THEN SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Some arithmetical combinations (more to prove).                           *)
(* ------------------------------------------------------------------------- *)


let OPEN_SCALING = 
prove
 (`!s:real^N->bool c. ~(c = &0) /\ open s ==> open(IMAGE (\x. c % x) s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_def; FORALL_IN_IMAGE] THEN
  STRIP_TAC THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `e * abs(c)` THEN ASM_SIMP_TAC[REAL_LT_MUL; GSYM REAL_ABS_NZ] THEN
  X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN REWRITE_TAC[IN_IMAGE] THEN
  EXISTS_TAC `inv(c) % y:real^N` THEN
  ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_RINV; VECTOR_MUL_LID] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  SUBGOAL_THEN `x = inv(c) % c % x:real^N` SUBST1_TAC THENL
   [ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; VECTOR_MUL_LID];
    REWRITE_TAC[dist; GSYM VECTOR_SUB_LDISTRIB; NORM_MUL] THEN
    ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN REWRITE_TAC[REAL_ABS_INV] THEN
    ASM_SIMP_TAC[GSYM real_div; REAL_LT_LDIV_EQ; GSYM REAL_ABS_NZ] THEN
    ASM_REWRITE_TAC[GSYM dist]]);;


let OPEN_NEGATIONS = 
prove
 (`!s:real^N->bool. open s ==> open (IMAGE (--) s)`,

  SUBGOAL_THEN `(--) = \x:real^N. --(&1) % x`
   (fun th -> SIMP_TAC[th; OPEN_SCALING; REAL_ARITH `~(--(&1) = &0)`]) THEN
  REWRITE_TAC[FUN_EQ_THM] THEN VECTOR_ARITH_TAC);;


let OPEN_TRANSLATION = 
prove
 (`!s a:real^N. open s ==> open(IMAGE (\x. a + x) s)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`\x:real^N. x - a`; `s:real^N->bool`]
         CONTINUOUS_OPEN_PREIMAGE_UNIV) THEN
  ASM_SIMP_TAC[CONTINUOUS_SUB; CONTINUOUS_AT_ID; CONTINUOUS_CONST] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE; IN_UNIV] THEN
  ASM_MESON_TAC[VECTOR_ARITH `(a + x) - a = x:real^N`;
                VECTOR_ARITH `a + (x - a) = x:real^N`]);;


let OPEN_TRANSLATION_EQ = 
prove
 (`!a s. open (IMAGE (\x:real^N. a + x) s) <=> open s`,

  REWRITE_TAC[open_def] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [OPEN_TRANSLATION_EQ];;


let OPEN_AFFINITY = 
prove
 (`!s a:real^N c.
        open s /\ ~(c = &0) ==> open (IMAGE (\x. a + c % x) s)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `(\x:real^N. a + c % x) = (\x. a + x) o (\x. c % x)`
  SUBST1_TAC THENL [REWRITE_TAC[o_DEF]; ALL_TAC] THEN
  ASM_SIMP_TAC[IMAGE_o; OPEN_TRANSLATION; OPEN_SCALING]);;


let INTERIOR_TRANSLATION = 
prove
 (`!a:real^N s.
    interior (IMAGE (\x. a + x) s) = IMAGE (\x. a + x) (interior s)`,

  REWRITE_TAC[interior] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [INTERIOR_TRANSLATION];;


let OPEN_SUMS = 
prove
 (`!s t:real^N->bool.
        open s \/ open t ==> open {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_def] THEN STRIP_TAC THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `y:real^N`] THEN STRIP_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`);
    FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`)] THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `e:real` THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  X_GEN_TAC `z:real^N` THEN DISCH_TAC THEN REWRITE_TAC[IN_ELIM_THM] THEN
  ASM_MESON_TAC[VECTOR_ADD_SYM; VECTOR_ARITH `(z - y) + y:real^N = z`;
                NORM_ARITH `dist(z:real^N,x + y) < e ==> dist(z - y,x) < e`]);;

(* ------------------------------------------------------------------------- *)
(* Upper and lower hemicontinuous functions, relation in the case of         *)
(* preimage map to open and closed maps, and fact that upper and lower       *)
(* hemicontinuity together imply continuity in the sense of the Hausdorff    *)
(* metric (at points where the function gives a bounded and nonempty set).   *)
(* ------------------------------------------------------------------------- *)


let UPPER_HEMICONTINUOUS = 
prove
 (`!f:real^M->real^N->bool t s.
        (!x. x IN s ==> f(x) SUBSET t)
        ==> ((!u. open_in (subtopology euclidean t) u
                  ==> open_in (subtopology euclidean s)
                              {x | x IN s /\ f(x) SUBSET u}) <=>
             (!u. closed_in (subtopology euclidean t) u
                  ==> closed_in (subtopology euclidean s)
                                {x | x IN s /\ ~(f(x) INTER u = {})}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN GEN_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `t DIFF u:real^N->bool`) THEN
  MATCH_MP_TAC MONO_IMP THEN
  SIMP_TAC[OPEN_IN_DIFF; CLOSED_IN_DIFF; OPEN_IN_REFL; CLOSED_IN_REFL] THENL
   [REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ]; REWRITE_TAC[closed_in]] THEN
  REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY; SUBSET_RESTRICT] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]);;


let LOWER_HEMICONTINUOUS = 
prove
 (`!f:real^M->real^N->bool t s.
        (!x. x IN s ==> f(x) SUBSET t)
        ==> ((!u. closed_in (subtopology euclidean t) u
                  ==> closed_in (subtopology euclidean s)
                                {x | x IN s /\ f(x) SUBSET u}) <=>
             (!u. open_in (subtopology euclidean t) u
                  ==> open_in (subtopology euclidean s)
                              {x | x IN s /\ ~(f(x) INTER u = {})}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN GEN_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `t DIFF u:real^N->bool`) THEN
  MATCH_MP_TAC MONO_IMP THEN
  SIMP_TAC[OPEN_IN_DIFF; CLOSED_IN_DIFF; OPEN_IN_REFL; CLOSED_IN_REFL] THENL
   [REWRITE_TAC[closed_in]; REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ]] THEN
  REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY; SUBSET_RESTRICT] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]);;


let OPEN_MAP_IFF_LOWER_HEMICONTINUOUS_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
        IMAGE f s SUBSET t
        ==> ((!u. open_in (subtopology euclidean s) u
                  ==> open_in (subtopology euclidean t) (IMAGE f u)) <=>
             (!u. closed_in (subtopology euclidean s) u
                      ==> closed_in (subtopology euclidean t)
                                    {y | y IN t /\
                                         {x | x IN s /\ f x = y} SUBSET u}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THENL
   [X_GEN_TAC `v:real^M->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `s DIFF v:real^M->bool`) THEN
    ASM_SIMP_TAC[OPEN_IN_DIFF; OPEN_IN_REFL] THEN
    REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[];
    X_GEN_TAC `v:real^M->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `s DIFF v:real^M->bool`) THEN
    ASM_SIMP_TAC[CLOSED_IN_DIFF; CLOSED_IN_REFL] THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
    REWRITE_TAC[OPEN_IN_CLOSED_IN_EQ; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
    DISCH_THEN(fun th -> CONJ_TAC THENL [ASM SET_TAC[]; MP_TAC th]) THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]]);;


let CLOSED_MAP_IFF_UPPER_HEMICONTINUOUS_PREIMAGE = 
prove
 (`!f:real^M->real^N s t.
        IMAGE f s SUBSET t
        ==> ((!u. closed_in (subtopology euclidean s) u
                  ==> closed_in (subtopology euclidean t) (IMAGE f u)) <=>
             (!u. open_in (subtopology euclidean s) u
                  ==> open_in (subtopology euclidean t)
                              {y | y IN t /\
                                   {x | x IN s /\ f x = y} SUBSET u}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THENL
   [X_GEN_TAC `v:real^M->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `s DIFF v:real^M->bool`) THEN
    ASM_SIMP_TAC[CLOSED_IN_DIFF; CLOSED_IN_REFL] THEN
    REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[];
    X_GEN_TAC `v:real^M->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `s DIFF v:real^M->bool`) THEN
    ASM_SIMP_TAC[OPEN_IN_DIFF; OPEN_IN_REFL] THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP CLOSED_IN_IMP_SUBSET) THEN
    REWRITE_TAC[closed_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
    DISCH_THEN(fun th -> CONJ_TAC THENL [ASM SET_TAC[]; MP_TAC th]) THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN ASM SET_TAC[]]);;


let UPPER_LOWER_HEMICONTINUOUS_EXPLICIT = 
prove
 (`!f:real^M->real^N->bool t s.
      (!x. x IN s ==> f(x) SUBSET t) /\
      (!u. open_in (subtopology euclidean t) u
           ==> open_in (subtopology euclidean s)
                       {x | x IN s /\ f(x) SUBSET u}) /\
      (!u. closed_in (subtopology euclidean t) u
           ==> closed_in (subtopology euclidean s)
                         {x | x IN s /\ f(x) SUBSET u})
      ==> !x e. x IN s /\ &0 < e /\ bounded(f x) /\ ~(f x = {})
                ==> ?d. &0 < d /\
                        !x'. x' IN s /\ dist(x,x') < d
                             ==> (!y. y IN f x
                                      ==> ?y'. y' IN f x' /\ dist(y,y') < e) /\
                                 (!y'. y' IN f x'
                                       ==> ?y. y IN f x /\ dist(y',y) < e)`,

  REPEAT STRIP_TAC THEN
  UNDISCH_TAC
   `!u. open_in (subtopology euclidean t) u
        ==> open_in (subtopology euclidean s)
                    {x | x IN s /\ (f:real^M->real^N->bool)(x) SUBSET u}` THEN
  DISCH_THEN(MP_TAC o SPEC
   `t INTER
    {a + b | a IN (f:real^M->real^N->bool) x /\ b IN ball(vec 0,e)}`) THEN
  SIMP_TAC[OPEN_SUMS; OPEN_BALL; OPEN_IN_OPEN_INTER] THEN
  REWRITE_TAC[open_in; SUBSET_RESTRICT] THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^M`) THEN
  ASM_SIMP_TAC[IN_ELIM_THM; SUBSET_INTER] THEN ANTS_TAC THENL
   [REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN
    ASM_MESON_TAC[CENTRE_IN_BALL; VECTOR_ADD_RID];
    DISCH_THEN(X_CHOOSE_THEN `d1:real`
     (CONJUNCTS_THEN2 ASSUME_TAC (LABEL_TAC "1")))] THEN
  UNDISCH_TAC
   `!u. closed_in (subtopology euclidean t) u
        ==> closed_in (subtopology euclidean s)
                    {x | x IN s /\ (f:real^M->real^N->bool)(x) SUBSET u}` THEN
  ASM_SIMP_TAC[LOWER_HEMICONTINUOUS] THEN DISCH_THEN(MP_TAC o
    GEN `a:real^N` o SPEC `t INTER ball(a:real^N,e / &2)`) THEN
  SIMP_TAC[OPEN_BALL; OPEN_IN_OPEN_INTER] THEN

  MP_TAC(SPEC `closure((f:real^M->real^N->bool) x)`
    COMPACT_EQ_HEINE_BOREL) THEN
  ASM_REWRITE_TAC[COMPACT_CLOSURE] THEN DISCH_THEN(MP_TAC o SPEC
   `{ball(a:real^N,e / &2) | a IN (f:real^M->real^N->bool) x}`) THEN
  REWRITE_TAC[SIMPLE_IMAGE; FORALL_IN_IMAGE; OPEN_BALL] THEN
  ONCE_REWRITE_TAC[TAUT `p /\ q /\ r <=> q /\ p /\ r`] THEN
  REWRITE_TAC[EXISTS_FINITE_SUBSET_IMAGE] THEN ANTS_TAC THENL
   [REWRITE_TAC[CLOSURE_APPROACHABLE; SUBSET; UNIONS_IMAGE; IN_ELIM_THM] THEN
    REWRITE_TAC[IN_BALL] THEN ASM_SIMP_TAC[REAL_HALF];
    ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `c:real^N->bool` STRIP_ASSUME_TAC) THEN
  DISCH_TAC THEN FIRST_X_ASSUM(ASSUME_TAC o MATCH_MP
   (MESON[CLOSURE_SUBSET; SUBSET_TRANS]
        `closure s SUBSET t ==> s SUBSET t`)) THEN
  SUBGOAL_THEN
   `open_in (subtopology euclidean s)
      (INTERS {{x | x IN s /\
          ~((f:real^M->real^N->bool) x INTER t INTER ball(a,e / &2) = {})} |
     a IN c})`
  MP_TAC THENL
   [MATCH_MP_TAC OPEN_IN_INTERS THEN
    ASM_SIMP_TAC[SIMPLE_IMAGE; FORALL_IN_IMAGE; FINITE_IMAGE] THEN
    ASM_REWRITE_TAC[IMAGE_EQ_EMPTY] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  REWRITE_TAC[open_in] THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^M` o CONJUNCT2) THEN ANTS_TAC THENL
   [REWRITE_TAC[INTERS_GSPEC; IN_ELIM_THM] THEN
    X_GEN_TAC `a:real^N` THEN DISCH_TAC THEN
    ASM_REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
    EXISTS_TAC `a:real^N` THEN
    ASM_REWRITE_TAC[IN_INTER; CENTRE_IN_BALL; REAL_HALF] THEN
    ASM SET_TAC[];
    DISCH_THEN(X_CHOOSE_THEN `d2:real`
     (CONJUNCTS_THEN2 ASSUME_TAC (LABEL_TAC "2")))] THEN
  EXISTS_TAC `min d1 d2:real` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  X_GEN_TAC `x':real^M` THEN STRIP_TAC THEN CONJ_TAC THENL
   [ALL_TAC;
    REMOVE_THEN "1" (MP_TAC o SPEC `x':real^M`) THEN
    ASM_REWRITE_TAC[] THEN
    ANTS_TAC THENL [ASM_MESON_TAC[DIST_SYM]; ALL_TAC] THEN
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_BALL] THEN
    REWRITE_TAC[VECTOR_ARITH `x:real^N = a + b <=> x - a = b`;
                DIST_0; ONCE_REWRITE_RULE[CONJ_SYM] UNWIND_THM1] THEN
    REWRITE_TAC[dist]] THEN
  REMOVE_THEN "2" (MP_TAC o SPEC `x':real^M`) THEN
  ASM_REWRITE_TAC[INTERS_GSPEC; IN_ELIM_THM] THEN
  ANTS_TAC THENL [ASM_MESON_TAC[DIST_SYM]; ALL_TAC] THEN
  DISCH_THEN(LABEL_TAC "3") THEN
  X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
  UNDISCH_TAC `(f:real^M->real^N->bool) x SUBSET
               UNIONS (IMAGE (\a. ball (a,e / &2)) c)` THEN
  REWRITE_TAC[SUBSET] THEN DISCH_THEN(MP_TAC o SPEC `y:real^N`) THEN
  ASM_REWRITE_TAC[UNIONS_IMAGE; IN_ELIM_THM; IN_BALL] THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^N` STRIP_ASSUME_TAC) THEN
  REMOVE_THEN "3" (MP_TAC o SPEC `a:real^N`) THEN
  ASM_REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_INTER; IN_BALL] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `z:real^N` THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[DIST_TRIANGLE_HALF_L; DIST_SYM]);;

(* ------------------------------------------------------------------------- *)
(* Connected components, considered as a "connectedness" relation or a set.  *)
(* ------------------------------------------------------------------------- *)


let connected_component = new_definition
 `connected_component s x y <=>
        ?t. connected t /\ t SUBSET s /\ x IN t /\ y IN t`;;


let CONNECTED_COMPONENT_IN = 
prove
 (`!s x y. connected_component s x y ==> x IN s /\ y IN s`,

  REWRITE_TAC[connected_component] THEN SET_TAC[]);;


let CONNECTED_COMPONENT_REFL = 
prove
 (`!s x:real^N. x IN s ==> connected_component s x x`,

  REWRITE_TAC[connected_component] THEN REPEAT STRIP_TAC THEN
  EXISTS_TAC `{x:real^N}` THEN REWRITE_TAC[CONNECTED_SING] THEN
  ASM SET_TAC[]);;


let CONNECTED_COMPONENT_REFL_EQ = 
prove
 (`!s x:real^N. connected_component s x x <=> x IN s`,

  REPEAT GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[CONNECTED_COMPONENT_REFL] THEN
  REWRITE_TAC[connected_component] THEN SET_TAC[]);;


let CONNECTED_COMPONENT_SYM = 
prove
 (`!s x y:real^N. connected_component s x y ==> connected_component s y x`,

  REWRITE_TAC[connected_component] THEN MESON_TAC[]);;


let CONNECTED_COMPONENT_TRANS = 
prove
 (`!s x y:real^N.
    connected_component s x y /\ connected_component s y z
    ==> connected_component s x z`,

  REPEAT GEN_TAC THEN REWRITE_TAC[connected_component] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (X_CHOOSE_TAC `t:real^N->bool`)
                             (X_CHOOSE_TAC `u:real^N->bool`)) THEN
  EXISTS_TAC `t UNION u:real^N->bool` THEN
  ASM_REWRITE_TAC[IN_UNION; UNION_SUBSET] THEN
  MATCH_MP_TAC CONNECTED_UNION THEN ASM SET_TAC[]);;


let CONNECTED_COMPONENT_OF_SUBSET = 
prove
 (`!s t x. s SUBSET t /\ connected_component s x y
           ==> connected_component t x y`,

  REWRITE_TAC[connected_component] THEN SET_TAC[]);;


let CONNECTED_COMPONENT_SET = 
prove
 (`!s x. connected_component s x =
            { y | ?t. connected t /\ t SUBSET s /\ x IN t /\ y IN t}`,

  REWRITE_TAC[IN_ELIM_THM; EXTENSION] THEN
  REWRITE_TAC[IN; connected_component] THEN MESON_TAC[]);;


let CONNECTED_COMPONENT_UNIONS = 
prove
 (`!s x. connected_component s x =
                UNIONS {t | connected t /\ x IN t /\ t SUBSET s}`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SET_TAC[]);;


let CONNECTED_COMPONENT_SUBSET = 
prove
 (`!s x. (connected_component s x) SUBSET s`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SET_TAC[]);;


let CONNECTED_CONNECTED_COMPONENT_SET = 
prove
 (`!s. connected s <=> !x:real^N. x IN s ==> connected_component s x = s`,

  GEN_TAC THEN REWRITE_TAC[CONNECTED_COMPONENT_UNIONS] THEN EQ_TAC THENL
   [SET_TAC[]; ALL_TAC] THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[CONNECTED_EMPTY] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^N` STRIP_ASSUME_TAC) THEN
  DISCH_THEN(MP_TAC o SPEC `a:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(SUBST1_TAC o SYM) THEN MATCH_MP_TAC CONNECTED_UNIONS THEN
  ASM SET_TAC[]);;


let CONNECTED_COMPONENT_EQ_SELF = 
prove
 (`!s x. connected s /\ x IN s ==> connected_component s x = s`,


let CONNECTED_IFF_CONNECTED_COMPONENT = 
prove
 (`!s. connected s <=>
          !x y. x IN s /\ y IN s ==> connected_component s x y`,

  REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT_SET] THEN
  REWRITE_TAC[EXTENSION] THEN MESON_TAC[IN; CONNECTED_COMPONENT_IN]);;


let CONNECTED_COMPONENT_MAXIMAL = 
prove
 (`!s t x:real^N.
        x IN t /\ connected t /\ t SUBSET s
        ==> t SUBSET (connected_component s x)`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SET_TAC[]);;


let CONNECTED_COMPONENT_MONO = 
prove
 (`!s t x. s SUBSET t
           ==> (connected_component s x) SUBSET (connected_component t x)`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SET_TAC[]);;


let CONNECTED_CONNECTED_COMPONENT = 
prove
 (`!s x. connected(connected_component s x)`,

  REWRITE_TAC[CONNECTED_COMPONENT_UNIONS] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_UNIONS THEN SET_TAC[]);;


let CONNECTED_COMPONENT_EQ_EMPTY = 
prove
 (`!s x:real^N. connected_component s x = {} <=> ~(x IN s)`,

  REPEAT GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[EXTENSION; NOT_IN_EMPTY] THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
    REWRITE_TAC[IN; CONNECTED_COMPONENT_REFL_EQ];
    REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SET_TAC[]]);;


let CONNECTED_COMPONENT_EMPTY = 
prove
 (`!x. connected_component {} x = {}`,


let CONNECTED_COMPONENT_EQ = 
prove
 (`!s x y. y IN connected_component s x
           ==> (connected_component s y = connected_component s x)`,


let CLOSED_CONNECTED_COMPONENT = 
prove
 (`!s x:real^N. closed s ==> closed(connected_component s x)`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `(x:real^N) IN s` THENL
   [ALL_TAC; ASM_MESON_TAC[CONNECTED_COMPONENT_EQ_EMPTY; CLOSED_EMPTY]] THEN
  REWRITE_TAC[GSYM CLOSURE_EQ] THEN
  MATCH_MP_TAC SUBSET_ANTISYM THEN REWRITE_TAC[CLOSURE_SUBSET] THEN
  MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN
  SIMP_TAC[CONNECTED_CLOSURE; CONNECTED_CONNECTED_COMPONENT] THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC(REWRITE_RULE[SUBSET] CLOSURE_SUBSET) THEN
    ASM_REWRITE_TAC[IN; CONNECTED_COMPONENT_REFL_EQ];
    MATCH_MP_TAC CLOSURE_MINIMAL THEN
    ASM_REWRITE_TAC[CONNECTED_COMPONENT_SUBSET]]);;


let CONNECTED_COMPONENT_DISJOINT = 
prove
 (`!s a b. DISJOINT (connected_component s a) (connected_component s b) <=>
             ~(a IN connected_component s b)`,

  REWRITE_TAC[DISJOINT; EXTENSION; IN_INTER; NOT_IN_EMPTY] THEN
  REWRITE_TAC[IN] THEN
  MESON_TAC[CONNECTED_COMPONENT_SYM; CONNECTED_COMPONENT_TRANS]);;


let CONNECTED_COMPONENT_NONOVERLAP = 
prove
 (`!s a b:real^N.
        (connected_component s a) INTER (connected_component s b) = {} <=>
        ~(a IN s) \/ ~(b IN s) \/
        ~(connected_component s a = connected_component s b)`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `(a:real^N) IN s` THEN ASM_REWRITE_TAC[] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM CONNECTED_COMPONENT_EQ_EMPTY]) THEN
  ASM_REWRITE_TAC[INTER_EMPTY] THEN
  ASM_CASES_TAC `(b:real^N) IN s` THEN ASM_REWRITE_TAC[] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM CONNECTED_COMPONENT_EQ_EMPTY]) THEN
  ASM_REWRITE_TAC[INTER_EMPTY] THEN ASM_CASES_TAC
   `connected_component s (a:real^N) = connected_component s b` THEN
  ASM_REWRITE_TAC[INTER_IDEMPOT; CONNECTED_COMPONENT_EQ_EMPTY] THEN
  FIRST_X_ASSUM(MP_TAC o check(is_neg o concl)) THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
  REWRITE_TAC[] THEN MATCH_MP_TAC CONNECTED_COMPONENT_EQ THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [GSYM DISJOINT]) THEN
  REWRITE_TAC[CONNECTED_COMPONENT_DISJOINT]);;


let CONNECTED_COMPONENT_OVERLAP = 
prove
 (`!s a b:real^N.
        ~((connected_component s a) INTER (connected_component s b) = {}) <=>
        a IN s /\ b IN s /\
        connected_component s a = connected_component s b`,

  REWRITE_TAC[CONNECTED_COMPONENT_NONOVERLAP; DE_MORGAN_THM]);;


let CONNECTED_COMPONENT_SYM_EQ = 
prove
 (`!s x y. connected_component s x y <=> connected_component s y x`,


let CONNECTED_COMPONENT_EQ_EQ = 
prove
 (`!s x y:real^N.
        connected_component s x = connected_component s y <=>
           ~(x IN s) /\ ~(y IN s) \/
           x IN s /\ y IN s /\ connected_component s x y`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `(y:real^N) IN s` THENL
   [ASM_CASES_TAC `(x:real^N) IN s` THEN ASM_REWRITE_TAC[] THENL
     [REWRITE_TAC[FUN_EQ_THM] THEN
      ASM_MESON_TAC[CONNECTED_COMPONENT_TRANS; CONNECTED_COMPONENT_REFL;
                    CONNECTED_COMPONENT_SYM];
      ASM_MESON_TAC[CONNECTED_COMPONENT_EQ_EMPTY]];
    RULE_ASSUM_TAC(REWRITE_RULE[GSYM CONNECTED_COMPONENT_EQ_EMPTY]) THEN
    ASM_REWRITE_TAC[CONNECTED_COMPONENT_EQ_EMPTY] THEN
    ONCE_REWRITE_TAC[CONNECTED_COMPONENT_SYM_EQ] THEN
    ASM_REWRITE_TAC[EMPTY] THEN ASM_MESON_TAC[CONNECTED_COMPONENT_EQ_EMPTY]]);;


let CONNECTED_EQ_CONNECTED_COMPONENT_EQ = 
prove
 (`!s. connected s <=>
       !x y. x IN s /\ y IN s
             ==> connected_component s x = connected_component s y`,


let CONNECTED_COMPONENT_IDEMP = 
prove
 (`!s x:real^N. connected_component (connected_component s x) x =
                connected_component s x`,

  REWRITE_TAC[FUN_EQ_THM; connected_component] THEN
  REPEAT GEN_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN EQ_TAC THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[CONNECTED_COMPONENT_MAXIMAL; SUBSET_TRANS;
                CONNECTED_COMPONENT_SUBSET]);;


let CONNECTED_COMPONENT_UNIQUE = 
prove
 (`!s c x:real^N.
        x IN c /\ c SUBSET s /\ connected c /\
        (!c'. x IN c' /\ c' SUBSET s /\ connected c'
              ==> c' SUBSET c)
        ==> connected_component s x = c`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
   [FIRST_X_ASSUM MATCH_MP_TAC THEN
    REWRITE_TAC[CONNECTED_COMPONENT_SUBSET; CONNECTED_CONNECTED_COMPONENT] THEN
    REWRITE_TAC[IN] THEN ASM_REWRITE_TAC[CONNECTED_COMPONENT_REFL_EQ] THEN
    ASM SET_TAC[];
    MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN ASM_REWRITE_TAC[]]);;


let JOINABLE_CONNECTED_COMPONENT_EQ = 
prove
 (`!s t x y:real^N.
        connected t /\ t SUBSET s /\
        ~(connected_component s x INTER t = {}) /\
        ~(connected_component s y INTER t = {})
        ==> connected_component s x = connected_component s y`,

  REPEAT GEN_TAC THEN
  REPLICATE_TAC 2 (DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_INTER] THEN DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `w:real^N` STRIP_ASSUME_TAC)
   (X_CHOOSE_THEN `z:real^N` STRIP_ASSUME_TAC)) THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_COMPONENT_EQ THEN
  REWRITE_TAC[IN] THEN
  MATCH_MP_TAC CONNECTED_COMPONENT_TRANS THEN
  EXISTS_TAC `z:real^N` THEN CONJ_TAC THENL [ASM_MESON_TAC[IN]; ALL_TAC] THEN
  MATCH_MP_TAC CONNECTED_COMPONENT_TRANS THEN
  EXISTS_TAC `w:real^N` THEN CONJ_TAC THENL
   [REWRITE_TAC[connected_component] THEN
    EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[];
    ASM_MESON_TAC[IN; CONNECTED_COMPONENT_SYM]]);;


let CONNECTED_COMPONENT_TRANSLATION = 
prove
 (`!a s x. connected_component (IMAGE (\x. a + x) s) (a + x) =
                IMAGE (\x. a + x) (connected_component s x)`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [CONNECTED_COMPONENT_TRANSLATION];;


let CONNECTED_COMPONENT_LINEAR_IMAGE = 
prove
 (`!f s x. linear f /\ (!x y. f x = f y ==> x = y) /\ (!y. ?x. f x = y)
           ==> connected_component (IMAGE f s) (f x) =
               IMAGE f (connected_component s x)`,

  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN
  GEOM_TRANSFORM_TAC[]);;

add_linear_invariants [CONNECTED_COMPONENT_LINEAR_IMAGE];;


let UNIONS_CONNECTED_COMPONENT = 
prove
 (`!s:real^N->bool. UNIONS {connected_component s x |x| x IN s} = s`,

  GEN_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  REWRITE_TAC[UNIONS_SUBSET; FORALL_IN_GSPEC; CONNECTED_COMPONENT_SUBSET] THEN
  REWRITE_TAC[SUBSET; UNIONS_GSPEC; IN_ELIM_THM] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN EXISTS_TAC `x:real^N` THEN
  ASM_REWRITE_TAC[] THEN REWRITE_TAC[IN] THEN
  ASM_REWRITE_TAC[CONNECTED_COMPONENT_REFL_EQ]);;


let COMPLEMENT_CONNECTED_COMPONENT_UNIONS = 
prove
 (`!s x:real^N.
     s DIFF connected_component s x =
     UNIONS({connected_component s y | y | y IN s} DELETE
            (connected_component s x))`,

  REPEAT GEN_TAC THEN
  GEN_REWRITE_TAC (LAND_CONV o LAND_CONV)
    [GSYM UNIONS_CONNECTED_COMPONENT] THEN
  MATCH_MP_TAC(SET_RULE
   `(!x. x IN s DELETE a ==> DISJOINT a x)
     ==> UNIONS s DIFF a = UNIONS (s DELETE a)`) THEN
  REWRITE_TAC[IMP_CONJ; FORALL_IN_GSPEC; IN_DELETE] THEN
  SIMP_TAC[CONNECTED_COMPONENT_DISJOINT; CONNECTED_COMPONENT_EQ_EQ] THEN
  MESON_TAC[IN; SUBSET; CONNECTED_COMPONENT_SUBSET]);;


let CLOSED_IN_CONNECTED_COMPONENT = 
prove
 (`!s x:real^N. closed_in (subtopology euclidean s) (connected_component s x)`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `connected_component s (x:real^N) = {}` THEN
  ASM_REWRITE_TAC[CLOSED_IN_EMPTY] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[CONNECTED_COMPONENT_EQ_EMPTY]) THEN
  REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  EXISTS_TAC `closure(connected_component s x):real^N->bool` THEN
  REWRITE_TAC[CLOSED_CLOSURE] THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  REWRITE_TAC[SUBSET_INTER; CONNECTED_COMPONENT_SUBSET; CLOSURE_SUBSET] THEN
  MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN REWRITE_TAC[INTER_SUBSET] THEN
  CONJ_TAC THENL
   [ASM_REWRITE_TAC[IN_INTER] THEN
    MATCH_MP_TAC(REWRITE_RULE[SUBSET] CLOSURE_SUBSET) THEN
    ASM_REWRITE_TAC[IN; CONNECTED_COMPONENT_REFL_EQ];
    MATCH_MP_TAC CONNECTED_INTERMEDIATE_CLOSURE THEN
    EXISTS_TAC `connected_component s (x:real^N)` THEN
    REWRITE_TAC[INTER_SUBSET; CONNECTED_CONNECTED_COMPONENT;
                SUBSET_INTER; CONNECTED_COMPONENT_SUBSET; CLOSURE_SUBSET]]);;


let OPEN_IN_CONNECTED_COMPONENT = 
prove
 (`!s x:real^N.
        FINITE {connected_component s x |x| x IN s}
        ==> open_in (subtopology euclidean s) (connected_component s x)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `connected_component s (x:real^N) =
        s DIFF (UNIONS {connected_component s y |y| y IN s} DIFF
                connected_component s x)`
  SUBST1_TAC THENL
   [REWRITE_TAC[UNIONS_CONNECTED_COMPONENT] THEN
    MATCH_MP_TAC(SET_RULE `t SUBSET s ==> t = s DIFF (s DIFF t)`) THEN
    REWRITE_TAC[CONNECTED_COMPONENT_SUBSET];
    MATCH_MP_TAC OPEN_IN_DIFF THEN
    REWRITE_TAC[OPEN_IN_SUBTOPOLOGY_REFL; TOPSPACE_EUCLIDEAN; SUBSET_UNIV] THEN
    REWRITE_TAC[UNIONS_DIFF] THEN
    MATCH_MP_TAC CLOSED_IN_UNIONS THEN REWRITE_TAC[FORALL_IN_GSPEC] THEN
    ONCE_REWRITE_TAC[SIMPLE_IMAGE] THEN ASM_SIMP_TAC[FINITE_IMAGE] THEN
    X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
    SUBGOAL_THEN
     `connected_component s y DIFF connected_component s x =
      connected_component s y \/
      connected_component s (y:real^N) DIFF connected_component s x = {}`
     (DISJ_CASES_THEN SUBST1_TAC)
    THENL
     [MATCH_MP_TAC(SET_RULE
       `(~(s INTER t = {}) ==> s = t) ==> s DIFF t = s \/ s DIFF t = {}`) THEN
      SIMP_TAC[CONNECTED_COMPONENT_OVERLAP];
      REWRITE_TAC[CLOSED_IN_CONNECTED_COMPONENT];
      REWRITE_TAC[CLOSED_IN_EMPTY]]]);;


let CONNECTED_COMPONENT_EQUIVALENCE_RELATION = 
prove
 (`!R s:real^N->bool.
        (!x y. R x y ==> R y x) /\
        (!x y z. R x y /\ R y z ==> R x z) /\
        (!a. a IN s
             ==> ?t. open_in (subtopology euclidean s) t /\ a IN t /\
                     !x. x IN t ==> R a x)
        ==> !a b. connected_component s a b ==> R a b`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`R:real^N->real^N->bool`; `connected_component s (a:real^N)`]
    CONNECTED_EQUIVALENCE_RELATION) THEN
  ASM_REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT] THEN ANTS_TAC THENL
   [X_GEN_TAC `c:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N`) THEN ANTS_TAC THENL
     [ASM_MESON_TAC[CONNECTED_COMPONENT_SUBSET; SUBSET]; ALL_TAC] THEN
    DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `t INTER connected_component s (a:real^N)` THEN
    ASM_SIMP_TAC[IN_INTER; OPEN_IN_OPEN] THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_IN_OPEN]) THEN
    MATCH_MP_TAC MONO_EXISTS THEN SIMP_TAC[] THEN
    MP_TAC(ISPECL [`s:real^N->bool`; `a:real^N`]
        CONNECTED_COMPONENT_SUBSET) THEN
    SET_TAC[];
    DISCH_THEN MATCH_MP_TAC THEN ASM_REWRITE_TAC[IN] THEN
    REWRITE_TAC[CONNECTED_COMPONENT_REFL_EQ] THEN
    ASM_MESON_TAC[CONNECTED_COMPONENT_IN]]);;


let CONNECTED_COMPONENT_INTERMEDIATE_SUBSET = 
prove
 (`!t u a:real^N.
        connected_component u a SUBSET t /\ t SUBSET u
        ==> connected_component t a = connected_component u a`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `(a:real^N) IN u` THENL
   [REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_COMPONENT_UNIQUE THEN
    ASM_REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT] THEN
    CONJ_TAC THENL [ASM_MESON_TAC[CONNECTED_COMPONENT_REFL; IN]; ALL_TAC] THEN
    REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN
    ASM SET_TAC[];
    ASM_MESON_TAC[CONNECTED_COMPONENT_EQ_EMPTY; SUBSET]]);;

(* ------------------------------------------------------------------------- *)
(* The set of connected components of a set.                                 *)
(* ------------------------------------------------------------------------- *)


let components = new_definition
  `components s = {connected_component s x | x | x:real^N IN s}`;;


let COMPONENTS_TRANSLATION = 
prove
 (`!a s. components(IMAGE (\x. a + x) s) =
   IMAGE (IMAGE (\x. a + x)) (components s)`,

  REWRITE_TAC[components] THEN GEOM_TRANSLATE_TAC[] THEN SET_TAC[]);;

add_translation_invariants [COMPONENTS_TRANSLATION];;


let COMPONENTS_LINEAR_IMAGE = 
prove
 (`!f s. linear f /\ (!x y. f x = f y ==> x = y) /\ (!y. ?x. f x = y)
           ==> components(IMAGE f s) = IMAGE (IMAGE f) (components s)`,

  REWRITE_TAC[components] THEN GEOM_TRANSFORM_TAC[] THEN SET_TAC[]);;

add_linear_invariants [COMPONENTS_LINEAR_IMAGE];;


let IN_COMPONENTS = 
prove
 (`!u:real^N->bool s. s IN components u
    <=> ?x. x IN u /\ s = connected_component u x`,

  REPEAT GEN_TAC THEN REWRITE_TAC[components] THEN EQ_TAC
  THENL [SET_TAC[];STRIP_TAC THEN ASM_SIMP_TAC[] THEN
  UNDISCH_TAC `x:real^N IN u` THEN SET_TAC[]]);;


let UNIONS_COMPONENTS = 
prove
 (`!u:real^N->bool. u = UNIONS (components u)`,

  REWRITE_TAC[EXTENSION] THEN REPEAT GEN_TAC THEN EQ_TAC
  THENL[DISCH_TAC THEN REWRITE_TAC[IN_UNIONS] THEN
  EXISTS_TAC `connected_component (u:real^N->bool) x` THEN CONJ_TAC THENL
  [REWRITE_TAC[components] THEN SET_TAC[ASSUME `x:real^N IN u`];
  REWRITE_TAC[CONNECTED_COMPONENT_SET] THEN SUBGOAL_THEN
  `?s:real^N->bool. connected s /\ s SUBSET u /\ x IN s` MP_TAC
  THENL[EXISTS_TAC `{x:real^N}` THEN ASM_REWRITE_TAC[CONNECTED_SING] THEN
  POP_ASSUM MP_TAC THEN SET_TAC[]; SET_TAC[]]];
  REWRITE_TAC[IN_UNIONS] THEN STRIP_TAC THEN
  MATCH_MP_TAC (SET_RULE `!x:real^N s u. x IN s /\ s SUBSET u ==> x IN u`) THEN
  EXISTS_TAC `t:real^N->bool` THEN ASM_REWRITE_TAC[] THEN STRIP_ASSUME_TAC
  (MESON[IN_COMPONENTS;ASSUME `t:real^N->bool IN components u`]
  `?y. t:real^N->bool = connected_component u y`) THEN
   ASM_REWRITE_TAC[CONNECTED_COMPONENT_SUBSET]]);;


let PAIRWISE_DISJOINT_COMPONENTS = 
prove
 (`!u:real^N->bool. pairwise DISJOINT (components u)`,

  GEN_TAC THEN REWRITE_TAC[pairwise;DISJOINT] THEN
  MAP_EVERY X_GEN_TAC [`s:real^N->bool`; `t:real^N->bool`] THEN STRIP_TAC THEN
  ASSERT_TAC `(?a. s:real^N->bool = connected_component u a) /\
  ?b. t:real^N->bool = connected_component u b`
  THENL [ASM_MESON_TAC[IN_COMPONENTS];
  ASM_MESON_TAC[CONNECTED_COMPONENT_NONOVERLAP]]);;


let IN_COMPONENTS_NONEMPTY = 
prove
 (`!s c. c IN components s ==> ~(c = {})`,

  REPEAT GEN_TAC THEN REWRITE_TAC[components; IN_ELIM_THM] THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[CONNECTED_COMPONENT_EQ_EMPTY]);;


let IN_COMPONENTS_SUBSET = 
prove
 (`!s c. c IN components s ==> c SUBSET s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[components; IN_ELIM_THM] THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[CONNECTED_COMPONENT_SUBSET]);;


let IN_COMPONENTS_CONNECTED = 
prove
 (`!s c. c IN components s ==> connected c`,

  REPEAT GEN_TAC THEN REWRITE_TAC[components; IN_ELIM_THM] THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT]);;


let IN_COMPONENTS_MAXIMAL = 
prove
 (`!s c:real^N->bool.
        c IN components s <=>
        ~(c = {}) /\ c SUBSET s /\ connected c /\
        !c'. ~(c' = {}) /\ c SUBSET c' /\ c' SUBSET s /\ connected c'
             ==> c' = c`,

  REPEAT GEN_TAC THEN REWRITE_TAC[components; IN_ELIM_THM] THEN EQ_TAC THENL
   [DISCH_THEN(X_CHOOSE_THEN `x:real^N` STRIP_ASSUME_TAC) THEN
    ASM_REWRITE_TAC[CONNECTED_COMPONENT_EQ_EMPTY; CONNECTED_COMPONENT_SUBSET;
                    CONNECTED_CONNECTED_COMPONENT] THEN
    REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
    ASM_REWRITE_TAC[] THEN MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN
    ASM_MESON_TAC[CONNECTED_COMPONENT_REFL; IN; SUBSET];
    STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `x:real^N` THEN
    DISCH_TAC THEN CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC(GSYM CONNECTED_COMPONENT_UNIQUE) THEN
    ASM_REWRITE_TAC[] THEN X_GEN_TAC `c':real^N->bool` THEN STRIP_TAC THEN
    REWRITE_TAC[SET_RULE `c' SUBSET c <=> c' UNION c = c`] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
    MATCH_MP_TAC CONNECTED_UNION THEN ASM SET_TAC[]]);;


let JOINABLE_COMPONENTS_EQ = 
prove
 (`!s t c1 c2.
        connected t /\ t SUBSET s /\
        c1 IN components s /\ c2 IN components s /\
        ~(c1 INTER t = {}) /\ ~(c2 INTER t = {})
        ==> c1 = c2`,

  REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM; components; FORALL_IN_GSPEC] THEN
  MESON_TAC[JOINABLE_CONNECTED_COMPONENT_EQ]);;


let CLOSED_IN_COMPONENT = 
prove
 (`!s c:real^N->bool.
        c IN components s ==> closed_in (subtopology euclidean s) c`,

  REWRITE_TAC[components; FORALL_IN_GSPEC; CLOSED_IN_CONNECTED_COMPONENT]);;


let CLOSED_COMPONENTS = 
prove
 (`!s c. closed s /\ c IN components s ==> closed c`,

  REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM; components; FORALL_IN_GSPEC] THEN
  SIMP_TAC[CLOSED_CONNECTED_COMPONENT]);;


let COMPACT_COMPONENTS = 
prove
 (`!s c:real^N->bool. compact s /\ c IN components s ==> compact c`,


let CONTINUOUS_ON_COMPONENTS_GEN = 
prove
 (`!f:real^M->real^N s.
        (!c. c IN components s
             ==> open_in (subtopology euclidean s) c /\ f continuous_on c)
        ==> f continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_OPEN_IN_PREIMAGE_EQ] THEN
  DISCH_TAC THEN X_GEN_TAC `t:real^N->bool` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ (f:real^M->real^N) x IN t} =
    UNIONS {{x | x IN c /\ f x IN t} | c IN components s}`
  SUBST1_TAC THENL
   [CONV_TAC(LAND_CONV(SUBS_CONV
     [ISPEC `s:real^M->bool` UNIONS_COMPONENTS])) THEN
    REWRITE_TAC[UNIONS_GSPEC; IN_UNIONS] THEN SET_TAC[];
    MATCH_MP_TAC OPEN_IN_UNIONS THEN REWRITE_TAC[FORALL_IN_GSPEC] THEN
    ASM_MESON_TAC[OPEN_IN_TRANS]]);;


let CONTINUOUS_ON_COMPONENTS_FINITE = 
prove
 (`!f:real^M->real^N s.
        FINITE(components s) /\
        (!c. c IN components s ==> f continuous_on c)
        ==> f continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONTINUOUS_CLOSED_IN_PREIMAGE_EQ] THEN
  DISCH_TAC THEN X_GEN_TAC `t:real^N->bool` THEN DISCH_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ (f:real^M->real^N) x IN t} =
    UNIONS {{x | x IN c /\ f x IN t} | c IN components s}`
  SUBST1_TAC THENL
   [CONV_TAC(LAND_CONV(SUBS_CONV
     [ISPEC `s:real^M->bool` UNIONS_COMPONENTS])) THEN
    REWRITE_TAC[UNIONS_GSPEC; IN_UNIONS] THEN SET_TAC[];
    MATCH_MP_TAC CLOSED_IN_UNIONS THEN
    ASM_SIMP_TAC[SIMPLE_IMAGE; FINITE_IMAGE; FORALL_IN_IMAGE] THEN
    ASM_MESON_TAC[CLOSED_IN_TRANS; CLOSED_IN_COMPONENT]]);;


let COMPONENTS_NONOVERLAP = 
prove
 (`!s c c'. c IN components s /\ c' IN components s
            ==> (c INTER c' = {} <=> ~(c = c'))`,

  REWRITE_TAC[components; IN_ELIM_THM] THEN REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[CONNECTED_COMPONENT_NONOVERLAP]);;


let COMPONENTS_EQ = 
prove
 (`!s c c'. c IN components s /\ c' IN components s
            ==> (c = c' <=> ~(c INTER c' = {}))`,

  MESON_TAC[COMPONENTS_NONOVERLAP]);;


let COMPONENTS_EQ_EMPTY = 
prove
 (`!s. components s = {} <=> s = {}`,

  GEN_TAC THEN REWRITE_TAC[EXTENSION] THEN
  REWRITE_TAC[components; connected_component; IN_ELIM_THM] THEN
  SET_TAC[]);;


let COMPONENTS_EMPTY = 
prove
 (`components {} = {}`,

  REWRITE_TAC[COMPONENTS_EQ_EMPTY]);;


let CONNECTED_EQ_CONNECTED_COMPONENTS_EQ = 
prove
 (`!s. connected s <=>
       !c c'. c IN components s /\ c' IN components s ==> c = c'`,

  REWRITE_TAC[components; IN_ELIM_THM] THEN
  MESON_TAC[CONNECTED_EQ_CONNECTED_COMPONENT_EQ]);;

let COMPONENTS_EQ_SING,COMPONENTS_EQ_SING_EXISTS = (CONJ_PAIR o prove)
 (`(!s:real^N->bool. components s = {s} <=> connected s /\ ~(s = {})) /\
   (!s:real^N->bool. (?a. components s = {a}) <=> connected s /\ ~(s = {}))`,
  REWRITE_TAC[AND_FORALL_THM] THEN X_GEN_TAC `s:real^N->bool` THEN
  MATCH_MP_TAC(TAUT `(p ==> q) /\ (q ==> r) /\ (r ==> p)
                     ==> (p <=> r) /\ (q <=> r)`) THEN
  REPEAT CONJ_TAC THENL
   [MESON_TAC[];
    STRIP_TAC THEN ASM_REWRITE_TAC[CONNECTED_EQ_CONNECTED_COMPONENTS_EQ] THEN
    ASM_MESON_TAC[IN_SING; COMPONENTS_EQ_EMPTY; NOT_INSERT_EMPTY];
    STRIP_TAC THEN ONCE_REWRITE_TAC[EXTENSION] THEN
    REWRITE_TAC[IN_SING] THEN
    REWRITE_TAC[components; IN_ELIM_THM] THEN
    ASM_MESON_TAC[CONNECTED_CONNECTED_COMPONENT_SET; MEMBER_NOT_EMPTY]]);;


let CONNECTED_EQ_COMPONENTS_SUBSET_SING = 
prove
 (`!s:real^N->bool. connected s <=> components s SUBSET {s}`,

  GEN_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[COMPONENTS_EMPTY; CONNECTED_EMPTY; EMPTY_SUBSET] THEN
  REWRITE_TAC[SET_RULE `s SUBSET {a} <=> s = {} \/ s = {a}`] THEN
  ASM_REWRITE_TAC[COMPONENTS_EQ_EMPTY; COMPONENTS_EQ_SING]);;


let CONNECTED_EQ_COMPONENTS_SUBSET_SING_EXISTS = 
prove
 (`!s:real^N->bool. connected s <=> ?a. components s SUBSET {a}`,

  GEN_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[COMPONENTS_EMPTY; CONNECTED_EMPTY; EMPTY_SUBSET] THEN
  REWRITE_TAC[SET_RULE `s SUBSET {a} <=> s = {} \/ s = {a}`] THEN
  ASM_REWRITE_TAC[COMPONENTS_EQ_EMPTY; COMPONENTS_EQ_SING_EXISTS]);;


let IN_COMPONENTS_SELF = 
prove
 (`!s:real^N->bool. s IN components s <=> connected s /\ ~(s = {})`,

  GEN_TAC THEN EQ_TAC THENL
   [MESON_TAC[IN_COMPONENTS_NONEMPTY; IN_COMPONENTS_CONNECTED];
    SIMP_TAC[GSYM COMPONENTS_EQ_SING; IN_SING]]);;


let COMPONENTS_MAXIMAL = 
prove
 (`!s t c:real^N->bool.
     c IN components s /\ connected t /\ t SUBSET s /\ ~(c INTER t = {})
     ==> t SUBSET c`,

  REWRITE_TAC[IMP_CONJ; components; FORALL_IN_GSPEC] THEN
  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
  REWRITE_TAC[IN_INTER; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  FIRST_ASSUM(SUBST1_TAC o SYM o MATCH_MP CONNECTED_COMPONENT_EQ) THEN
  MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN ASM_REWRITE_TAC[]);;


let COMPONENTS_UNIQUE = 
prove
 (`!s:real^N->bool k.
        UNIONS k = s /\
        (!c. c IN k
             ==> connected c /\ ~(c = {}) /\
                 !c'. connected c' /\ c SUBSET c' /\ c' SUBSET s ==> c' = c)
        ==> components s = k`,

  REPEAT STRIP_TAC THEN GEN_REWRITE_TAC I [EXTENSION] THEN
  X_GEN_TAC `c:real^N->bool` THEN REWRITE_TAC[IN_COMPONENTS] THEN
  EQ_TAC THENL
   [DISCH_THEN(X_CHOOSE_THEN `x:real^N`
     (CONJUNCTS_THEN2 ASSUME_TAC SUBST1_TAC)) THEN
    FIRST_ASSUM(MP_TAC o SPEC `x:real^N` o GEN_REWRITE_RULE I [EXTENSION]) THEN
    REWRITE_TAC[IN_UNIONS] THEN ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `c:real^N->bool` THEN STRIP_TAC THEN
    SUBGOAL_THEN `connected_component s (x:real^N) = c`
     (fun th -> ASM_REWRITE_TAC[th]) THEN
    MATCH_MP_TAC CONNECTED_COMPONENT_UNIQUE THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N->bool`) THEN
    ASM_REWRITE_TAC[] THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    X_GEN_TAC `c':real^N->bool` THEN STRIP_TAC THEN
    REWRITE_TAC[SET_RULE `c' SUBSET c <=> c' UNION c = c`] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN CONJ_TAC THENL
     [MATCH_MP_TAC CONNECTED_UNION; ASM SET_TAC[]] THEN
    ASM SET_TAC[];
    DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N->bool`) THEN
    ASM_REWRITE_TAC[] THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `x:real^N` THEN STRIP_TAC THEN
    CONJ_TAC THENL [ASM SET_TAC[]; CONV_TAC SYM_CONV] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN
    REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT; CONNECTED_COMPONENT_SUBSET] THEN
    MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN
    ASM_REWRITE_TAC[] THEN ASM SET_TAC[]]);;


let COMPONENTS_UNIQUE_EQ = 
prove
 (`!s:real^N->bool k.
        components s = k <=>
        UNIONS k = s /\
        (!c. c IN k
             ==> connected c /\ ~(c = {}) /\
                 !c'. connected c' /\ c SUBSET c' /\ c' SUBSET s ==> c' = c)`,

  REPEAT GEN_TAC THEN EQ_TAC THENL
   [DISCH_THEN(SUBST1_TAC o SYM); REWRITE_TAC[COMPONENTS_UNIQUE]] THEN
  REWRITE_TAC[GSYM UNIONS_COMPONENTS] THEN
  X_GEN_TAC `c:real^N->bool` THEN DISCH_TAC THEN REPEAT CONJ_TAC THENL
   [ASM_MESON_TAC[IN_COMPONENTS_CONNECTED];
    ASM_MESON_TAC[IN_COMPONENTS_NONEMPTY];
    RULE_ASSUM_TAC(REWRITE_RULE[IN_COMPONENTS_MAXIMAL]) THEN
    ASM_MESON_TAC[SUBSET_EMPTY]]);;


let EXISTS_COMPONENT_SUPERSET = 
prove
 (`!s t:real^N->bool.
        t SUBSET s /\ ~(s = {}) /\ connected t
        ==> ?c. c IN components s /\ t SUBSET c`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `t:real^N->bool = {}` THENL
   [ASM_REWRITE_TAC[EMPTY_SUBSET] THEN
    ASM_MESON_TAC[COMPONENTS_EQ_EMPTY; MEMBER_NOT_EMPTY];
    FIRST_X_ASSUM(X_CHOOSE_TAC `a:real^N` o
      GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    EXISTS_TAC `connected_component s (a:real^N)` THEN
    REWRITE_TAC[IN_COMPONENTS] THEN CONJ_TAC THENL
     [ASM SET_TAC[]; ASM_MESON_TAC[CONNECTED_COMPONENT_MAXIMAL]]]);;


let COMPONENTS_INTERMEDIATE_SUBSET = 
prove
 (`!s t u:real^N->bool.
        s IN components u /\ s SUBSET t /\ t SUBSET u
        ==> s IN components t`,


let IN_COMPONENTS_UNIONS_COMPLEMENT = 
prove
 (`!s c:real^N->bool.
        c IN components s
        ==> s DIFF c = UNIONS(components s DELETE c)`,


let CONNECTED_SUBSET_CLOPEN = 
prove
 (`!u s c:real^N->bool.
        closed_in (subtopology euclidean u) s /\
        open_in (subtopology euclidean u) s /\
        connected c /\ c SUBSET u /\ ~(c INTER s = {})
        ==> c SUBSET s`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CONNECTED_CLOSED_IN]) THEN
  REWRITE_TAC[NOT_EXISTS_THM] THEN DISCH_THEN(MP_TAC o
    SPECL [`c INTER s:real^N->bool`; `c DIFF s:real^N->bool`]) THEN
  ASM_REWRITE_TAC[CONJ_ASSOC; SET_RULE `c DIFF s = {} <=> c SUBSET s`] THEN
  MATCH_MP_TAC(TAUT `p ==> ~(p /\ ~q) ==> q`) THEN
  REPLICATE_TAC 2 (CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]]) THEN
  CONJ_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CLOSED_IN_CLOSED]);
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_IN_OPEN])] THEN
  DISCH_THEN(X_CHOOSE_THEN `t:real^N->bool` STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[OPEN_IN_OPEN; CLOSED_IN_CLOSED] THENL
   [EXISTS_TAC `t:real^N->bool`; EXISTS_TAC `(:real^N) DIFF t`] THEN
  ASM_REWRITE_TAC[GSYM OPEN_CLOSED] THEN ASM SET_TAC[]);;


let CLOPEN_UNIONS_COMPONENTS = 
prove
 (`!u s:real^N->bool.
        closed_in (subtopology euclidean u) s /\
        open_in (subtopology euclidean u) s
        ==> ?k. k SUBSET components u /\ s = UNIONS k`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `{c:real^N->bool | c IN components u /\ ~(c INTER s = {})}` THEN
  REWRITE_TAC[SUBSET_RESTRICT] THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  CONJ_TAC THENL
   [MP_TAC(ISPEC `u:real^N->bool` UNIONS_COMPONENTS) THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN SET_TAC[];
    REWRITE_TAC[UNIONS_SUBSET; FORALL_IN_GSPEC] THEN
    REPEAT STRIP_TAC THEN MATCH_MP_TAC CONNECTED_SUBSET_CLOPEN THEN
    EXISTS_TAC `u:real^N->bool` THEN
    ASM_MESON_TAC[IN_COMPONENTS_CONNECTED; IN_COMPONENTS_SUBSET]]);;


let CLOPEN_IN_COMPONENTS = 
prove
 (`!u s:real^N->bool.
        closed_in (subtopology euclidean u) s /\
        open_in (subtopology euclidean u) s /\
        connected s /\ ~(s = {})
        ==> s IN components u`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[CONJ_ASSOC] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CLOPEN_UNIONS_COMPONENTS) THEN
  DISCH_THEN(X_CHOOSE_THEN `k:(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
  ASM_CASES_TAC `k:(real^N->bool)->bool = {}` THEN
  ASM_REWRITE_TAC[UNIONS_0] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
  DISCH_THEN(X_CHOOSE_TAC `c:real^N->bool`) THEN
  ASM_CASES_TAC `k = {c:real^N->bool}` THENL
   [ASM_MESON_TAC[UNIONS_1; GSYM SING_SUBSET]; ALL_TAC] THEN
  MATCH_MP_TAC(TAUT `~p ==> p /\ q ==> r`) THEN
  SUBGOAL_THEN `?c':real^N->bool. c' IN k /\ ~(c = c')` STRIP_ASSUME_TAC THENL
   [ASM_MESON_TAC[SET_RULE
     `a IN s /\ ~(s = {a}) ==> ?b. b IN s /\ ~(b = a)`];
    REWRITE_TAC[CONNECTED_EQ_CONNECTED_COMPONENTS_EQ] THEN
    DISCH_THEN(MP_TAC o SPECL [`c:real^N->bool`; `c':real^N->bool`]) THEN
    ASM_REWRITE_TAC[NOT_IMP] THEN CONJ_TAC THEN
    MATCH_MP_TAC COMPONENTS_INTERMEDIATE_SUBSET THEN
    EXISTS_TAC `u:real^N->bool` THEN
    MP_TAC(ISPEC `u:real^N->bool` UNIONS_COMPONENTS) THEN ASM SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Continuity implies uniform continuity on a compact domain.                *)
(* ------------------------------------------------------------------------- *)


let COMPACT_UNIFORMLY_EQUICONTINUOUS = 
prove
 (`!(fs:(real^M->real^N)->bool) s.
     (!x e. x IN s /\ &0 < e
            ==> ?d. &0 < d /\
                    (!f x'. f IN fs /\ x' IN s /\ dist (x',x) < d
                            ==> dist (f x',f x) < e)) /\
     compact s
     ==> !e. &0 < e
             ==> ?d. &0 < d /\
                     !f x x'. f IN fs /\ x IN s /\ x' IN s /\ dist (x',x) < d
                              ==> dist(f x',f x) < e`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `d:real^M->real->real` THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o MATCH_MP HEINE_BOREL_LEMMA) THEN
  DISCH_THEN(MP_TAC o SPEC
    `{ ball(x:real^M,d x (e / &2)) | x IN s}`) THEN
  SIMP_TAC[FORALL_IN_GSPEC; OPEN_BALL; UNIONS_GSPEC; SUBSET; IN_ELIM_THM] THEN
  ANTS_TAC THENL [ASM_MESON_TAC[CENTRE_IN_BALL; REAL_HALF]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `k:real` THEN STRIP_TAC THEN
  ASM_REWRITE_TAC[] THEN
  MAP_EVERY X_GEN_TAC [`f:real^M->real^N`; `u:real^M`; `v:real^M`] THEN
  STRIP_TAC THEN FIRST_X_ASSUM(fun th -> MP_TAC(SPEC `v:real^M` th) THEN
    ASM_REWRITE_TAC[] THEN DISCH_THEN(CHOOSE_THEN MP_TAC)) THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(fun th ->
    MP_TAC(SPEC `u:real^M` th) THEN MP_TAC(SPEC `v:real^M` th)) THEN
  ASM_REWRITE_TAC[DIST_REFL] THEN
  FIRST_X_ASSUM(X_CHOOSE_THEN `w:real^M` (CONJUNCTS_THEN2 ASSUME_TAC
    SUBST_ALL_TAC)) THEN
  ASM_REWRITE_TAC[CENTRE_IN_BALL] THEN ASM_REWRITE_TAC[IN_BALL] THEN
  ONCE_REWRITE_TAC[DIST_SYM] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`w:real^M`; `e / &2`]) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(MP_TAC o SPEC `f:real^M->real^N` o CONJUNCT2) THEN
  DISCH_THEN(fun th -> MP_TAC(SPEC `u:real^M` th) THEN
                        MP_TAC(SPEC `v:real^M` th)) THEN
  ASM_REWRITE_TAC[] THEN CONV_TAC NORM_ARITH);;


let COMPACT_UNIFORMLY_CONTINUOUS = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s /\ compact s ==> f uniformly_continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous_on; uniformly_continuous_on] THEN
  STRIP_TAC THEN
  MP_TAC(ISPECL [`{f:real^M->real^N}`; `s:real^M->bool`]
        COMPACT_UNIFORMLY_EQUICONTINUOUS) THEN
  REWRITE_TAC[RIGHT_FORALL_IMP_THM; IMP_CONJ; IN_SING; FORALL_UNWIND_THM2] THEN
  ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* A uniformly convergent limit of continuous functions is continuous.       *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_UNIFORM_LIMIT = 
prove
 (`!net f:A->real^M->real^N g s.
        ~(trivial_limit net) /\
        eventually (\n. (f n) continuous_on s) net /\
        (!e. &0 < e
             ==> eventually (\n. !x. x IN s ==> norm(f n x - g x) < e) net)
        ==> g continuous_on s`,

  REWRITE_TAC[continuous_on] THEN REPEAT GEN_TAC THEN STRIP_TAC THEN
  X_GEN_TAC `x:real^M` THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &3`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; ARITH] THEN
  FIRST_X_ASSUM(fun th -> MP_TAC th THEN REWRITE_TAC[IMP_IMP] THEN
        GEN_REWRITE_TAC LAND_CONV [GSYM EVENTUALLY_AND]) THEN
  DISCH_THEN(MP_TAC o MATCH_MP EVENTUALLY_HAPPENS) THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `a:A` THEN
  DISCH_THEN(CONJUNCTS_THEN2 (MP_TAC o SPEC `x:real^M`) ASSUME_TAC) THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN(MP_TAC o SPEC `e / &3`) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; ARITH] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `d:real` THEN
  MATCH_MP_TAC MONO_AND THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `y:real^M` THEN
  DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN ASM_REWRITE_TAC[] THEN
  FIRST_X_ASSUM(fun th ->
   MP_TAC(SPEC `x:real^M` th) THEN MP_TAC(SPEC `y:real^M` th)) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC(REAL_ARITH
   `w <= x + y + z
    ==> x < e / &3 ==> y < e / &3 ==> z < e / &3 ==> w < e`) THEN
  REWRITE_TAC[dist] THEN
  SUBST1_TAC(VECTOR_ARITH
   `(g:real^M->real^N) y - g x =
    --(f (a:A) y - g y) + (f a x - g x) + (f a y - f a x)`) THEN
  MATCH_MP_TAC NORM_TRIANGLE_LE THEN REWRITE_TAC[NORM_NEG; REAL_LE_LADD] THEN
  MATCH_MP_TAC NORM_TRIANGLE_LE THEN REWRITE_TAC[NORM_NEG; REAL_LE_REFL]);;

(* ------------------------------------------------------------------------- *)
(* Topological stuff lifted from and dropped to R                            *)
(* ------------------------------------------------------------------------- *)


let OPEN_LIFT = 
prove
 (`!s. open(IMAGE lift s) <=>
        !x. x IN s ==> ?e. &0 < e /\ !x'. abs(x' - x) < e ==> x' IN s`,


let LIMPT_APPROACHABLE_LIFT = 
prove
 (`!x s. (lift x) limit_point_of (IMAGE lift s) <=>
         !e. &0 < e ==> ?x'. x' IN s /\ ~(x' = x) /\ abs(x' - x) < e`,


let CLOSED_LIFT = 
prove
 (`!s. closed (IMAGE lift s) <=>
        !x. (!e. &0 < e ==> ?x'. x' IN s /\ ~(x' = x) /\ abs(x' - x) < e)
            ==> x IN s`,

  GEN_TAC THEN REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE] THEN
  ONCE_REWRITE_TAC[FORALL_LIFT] THEN
  REWRITE_TAC[LIMPT_APPROACHABLE_LIFT; LIFT_EQ; DIST_LIFT;
              EXISTS_LIFT; LIFT_IN_IMAGE_LIFT]);;


let CONTINUOUS_AT_LIFT_RANGE = 
prove
 (`!f x. (lift o f) continuous (at x) <=>
                !e. &0 < e
                    ==> ?d. &0 < d /\
                            (!x'. norm(x' - x) < d
                                  ==> abs(f x' - f x) < e)`,

  REWRITE_TAC[continuous_at; o_THM; DIST_LIFT] THEN REWRITE_TAC[dist]);;


let CONTINUOUS_ON_LIFT_RANGE = 
prove
 (`!f s. (lift o f) continuous_on s <=>
         !x. x IN s
             ==> !e. &0 < e
                     ==> ?d. &0 < d /\
                             (!x'. x' IN s /\ norm(x' - x) < d
                                   ==> abs(f x' - f x) < e)`,

  REWRITE_TAC[continuous_on; o_THM; DIST_LIFT] THEN REWRITE_TAC[dist]);;


let CONTINUOUS_LIFT_NORM_COMPOSE = 
prove
 (`!net f:A->real^N.
        f continuous net
        ==> (\x. lift(norm(f x))) continuous net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[continuous; tendsto] THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN MATCH_MP_TAC MONO_IMP THEN
  REWRITE_TAC[] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
  REWRITE_TAC[DIST_REAL; GSYM drop; LIFT_DROP] THEN
  NORM_ARITH_TAC);;


let CONTINUOUS_ON_LIFT_NORM_COMPOSE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s
        ==> (\x. lift(norm(f x))) continuous_on s`,


let CONTINUOUS_AT_LIFT_NORM = 
prove
 (`!x. (lift o norm) continuous (at x)`,


let CONTINUOUS_ON_LIFT_NORM = 
prove
 (`!s. (lift o norm) continuous_on s`,


let CONTINUOUS_AT_LIFT_COMPONENT = 
prove
 (`!i a. 1 <= i /\ i <= dimindex(:N)
         ==> (\x:real^N. lift(x$i)) continuous (at a)`,


let CONTINUOUS_ON_LIFT_COMPONENT = 
prove
 (`!i s. 1 <= i /\ i <= dimindex(:N)
         ==> (\x:real^N. lift(x$i)) continuous_on s`,


let CONTINUOUS_AT_LIFT_INFNORM = 
prove
 (`!x:real^N. (lift o infnorm) continuous (at x)`,


let CONTINUOUS_AT_LIFT_DIST = 
prove
 (`!a:real^N x. (lift o (\x. dist(a,x))) continuous (at x)`,

  REWRITE_TAC[CONTINUOUS_AT_LIFT_RANGE] THEN
  MESON_TAC[NORM_ARITH `abs(dist(a:real^N,x) - dist(a,y)) <= norm(x - y)`;
            REAL_LET_TRANS]);;


let CONTINUOUS_ON_LIFT_DIST = 
prove
 (`!a s. (lift o (\x. dist(a,x))) continuous_on s`,

  REWRITE_TAC[CONTINUOUS_ON_LIFT_RANGE] THEN
  MESON_TAC[NORM_ARITH `abs(dist(a:real^N,x) - dist(a,y)) <= norm(x - y)`;
            REAL_LET_TRANS]);;

(* ------------------------------------------------------------------------- *)
(* Hence some handy theorems on distance, diameter etc. of/from a set.       *)
(* ------------------------------------------------------------------------- *)


let COMPACT_ATTAINS_SUP = 
prove
 (`!s. compact (IMAGE lift s) /\ ~(s = {})
       ==> ?x. x IN s /\ !y. y IN s ==> y <= x`,

  REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN REPEAT STRIP_TAC THEN
  MP_TAC(SPEC `s:real->bool` BOUNDED_HAS_SUP) THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN EXISTS_TAC `sup s` THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[CLOSED_LIFT; REAL_ARITH `s <= s - e <=> ~(&0 < e)`;
                REAL_ARITH `x <= s /\ ~(x <= s - e) ==> abs(x - s) < e`]);;


let COMPACT_ATTAINS_INF = 
prove
 (`!s. compact (IMAGE lift s) /\ ~(s = {})
       ==> ?x. x IN s /\ !y. y IN s ==> x <= y`,

  REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN REPEAT STRIP_TAC THEN
  MP_TAC(SPEC `s:real->bool` BOUNDED_HAS_INF) THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN EXISTS_TAC `inf s` THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[CLOSED_LIFT; REAL_ARITH `s + e <= s <=> ~(&0 < e)`;
                REAL_ARITH `s <= x /\ ~(s + e <= x) ==> abs(x - s) < e`]);;


let CONTINUOUS_ATTAINS_SUP = 
prove
 (`!f:real^N->real s.
        compact s /\ ~(s = {}) /\ (lift o f) continuous_on s
        ==> ?x. x IN s /\ !y. y IN s ==> f(y) <= f(x)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPEC `IMAGE (f:real^N->real) s` COMPACT_ATTAINS_SUP) THEN
  ASM_SIMP_TAC[GSYM IMAGE_o; COMPACT_CONTINUOUS_IMAGE; IMAGE_EQ_EMPTY] THEN
  MESON_TAC[IN_IMAGE]);;


let CONTINUOUS_ATTAINS_INF = 
prove
 (`!f:real^N->real s.
        compact s /\ ~(s = {}) /\ (lift o f) continuous_on s
        ==> ?x. x IN s /\ !y. y IN s ==> f(x) <= f(y)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPEC `IMAGE (f:real^N->real) s` COMPACT_ATTAINS_INF) THEN
  ASM_SIMP_TAC[GSYM IMAGE_o; COMPACT_CONTINUOUS_IMAGE; IMAGE_EQ_EMPTY] THEN
  MESON_TAC[IN_IMAGE]);;


let DISTANCE_ATTAINS_SUP = 
prove
 (`!s a. compact s /\ ~(s = {})
         ==> ?x. x IN s /\ !y. y IN s ==> dist(a,y) <= dist(a,x)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ATTAINS_SUP THEN
  ASM_REWRITE_TAC[CONTINUOUS_ON_LIFT_RANGE] THEN REWRITE_TAC[dist] THEN
  ASM_MESON_TAC[REAL_LET_TRANS; REAL_ABS_SUB_NORM; NORM_NEG;
                VECTOR_ARITH `(a - x) - (a - y) = --(x - y):real^N`]);;

(* ------------------------------------------------------------------------- *)
(* For *minimal* distance, we only need closure, not compactness.            *)
(* ------------------------------------------------------------------------- *)


let DISTANCE_ATTAINS_INF = 
prove
 (`!s a:real^N.
        closed s /\ ~(s = {})
        ==> ?x. x IN s /\ !y. y IN s ==> dist(a,x) <= dist(a,y)`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
  DISCH_THEN(X_CHOOSE_TAC `b:real^N`) THEN
  MP_TAC(ISPECL [`\x:real^N. dist(a,x)`; `cball(a:real^N,dist(b,a)) INTER s`]
                CONTINUOUS_ATTAINS_INF) THEN
  ANTS_TAC THENL
   [ASM_SIMP_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_INTER; BOUNDED_INTER;
                 BOUNDED_CBALL; CLOSED_CBALL; GSYM MEMBER_NOT_EMPTY] THEN
    REWRITE_TAC[dist; CONTINUOUS_ON_LIFT_RANGE; IN_INTER; IN_CBALL] THEN
    ASM_MESON_TAC[REAL_LET_TRANS; REAL_ABS_SUB_NORM; NORM_NEG; REAL_LE_REFL;
            NORM_SUB; VECTOR_ARITH `(a - x) - (a - y) = --(x - y):real^N`];
    MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[IN_INTER; IN_CBALL] THEN
    ASM_MESON_TAC[DIST_SYM; REAL_LE_TOTAL; REAL_LE_TRANS]]);;

(* ------------------------------------------------------------------------- *)
(* We can now extend limit compositions to consider the scalar multiplier.   *)
(* ------------------------------------------------------------------------- *)


let LIM_MUL = 
prove
 (`!net:(A)net f l:real^N c d.
        ((lift o c) --> lift d) net /\ (f --> l) net
        ==> ((\x. c(x) % f(x)) --> (d % l)) net`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`net:(A)net`; `\x (y:real^N). drop x % y`;
  `lift o (c:A->real)`; `f:A->real^N`; `lift d`; `l:real^N`] LIM_BILINEAR) THEN
  ASM_REWRITE_TAC[LIFT_DROP; o_THM] THEN DISCH_THEN MATCH_MP_TAC THEN
  REWRITE_TAC[bilinear; linear; DROP_ADD; DROP_CMUL] THEN
  REPEAT STRIP_TAC THEN VECTOR_ARITH_TAC);;


let LIM_VMUL = 
prove
 (`!net:(A)net c d v:real^N.
        ((lift o c) --> lift d) net ==> ((\x. c(x) % v) --> d % v) net`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_MUL THEN ASM_REWRITE_TAC[LIM_CONST]);;


let CONTINUOUS_VMUL = 
prove
 (`!net c v. (lift o c) continuous net ==> (\x. c(x) % v) continuous net`,

  REWRITE_TAC[continuous; LIM_VMUL; o_THM]);;


let CONTINUOUS_MUL = 
prove
 (`!net f c. (lift o c) continuous net /\ f continuous net
             ==> (\x. c(x) % f(x)) continuous net`,

  REWRITE_TAC[continuous; LIM_MUL; o_THM]);;


let CONTINUOUS_ON_VMUL = 
prove
 (`!s c v. (lift o c) continuous_on s ==> (\x. c(x) % v) continuous_on s`,

  REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  SIMP_TAC[CONTINUOUS_VMUL]);;


let CONTINUOUS_ON_MUL = 
prove
 (`!s c f. (lift o c) continuous_on s /\ f continuous_on s
           ==> (\x. c(x) % f(x)) continuous_on s`,

  REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  SIMP_TAC[CONTINUOUS_MUL]);;


let CONTINUOUS_LIFT_POW = 
prove
 (`!net f:A->real n.
        (\x. lift(f x)) continuous net
        ==> (\x. lift(f x pow n)) continuous net`,

  REWRITE_TAC[RIGHT_FORALL_IMP_THM] THEN REPEAT GEN_TAC THEN DISCH_TAC THEN
  INDUCT_TAC THEN ASM_REWRITE_TAC[LIFT_CMUL; real_pow; CONTINUOUS_CONST] THEN
  MATCH_MP_TAC CONTINUOUS_MUL THEN ASM_REWRITE_TAC[o_DEF]);;


let CONTINUOUS_ON_LIFT_POW = 
prove
 (`!f:real^N->real s n.
        (\x. lift(f x)) continuous_on s
        ==> (\x. lift(f x pow n)) continuous_on s`,

  REWRITE_TAC[RIGHT_FORALL_IMP_THM] THEN REPEAT GEN_TAC THEN
  DISCH_TAC THEN INDUCT_TAC THEN
  ASM_REWRITE_TAC[LIFT_CMUL; real_pow; CONTINUOUS_ON_CONST] THEN
  MATCH_MP_TAC CONTINUOUS_ON_MUL THEN ASM_REWRITE_TAC[o_DEF]);;


let CONTINUOUS_LIFT_PRODUCT = 
prove
 (`!net:(A)net f (t:B->bool).
        FINITE t /\
        (!i. i IN t ==> (\x. lift(f x i)) continuous net)
        ==> (\x. lift(product t (f x))) continuous net`,

  GEN_TAC THEN GEN_TAC THEN REWRITE_TAC[IMP_CONJ] THEN
  MATCH_MP_TAC FINITE_INDUCT_STRONG THEN SIMP_TAC[PRODUCT_CLAUSES] THEN
  REWRITE_TAC[CONTINUOUS_CONST; LIFT_CMUL; FORALL_IN_INSERT] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_MUL THEN
  ASM_SIMP_TAC[o_DEF]);;


let CONTINUOUS_ON_LIFT_PRODUCT = 
prove
 (`!f:real^N->A->real s t.
        FINITE t /\

        (!i. i IN t ==> (\x. lift(f x i)) continuous_on s)
        ==> (\x. lift(product t (f x))) continuous_on s`,

(* ------------------------------------------------------------------------- *)
(* And so we have continuity of inverse.                                     *)
(* ------------------------------------------------------------------------- *)


let LIM_INV = 
prove
 (`!net:(A)net f l.
        ((lift o f) --> lift l) net /\ ~(l = &0)
        ==> ((lift o inv o f) --> lift(inv l)) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM] THEN
  ASM_CASES_TAC `trivial_limit(net:(A)net)` THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[o_THM; DIST_LIFT] THEN STRIP_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `min (abs(l) / &2) ((l pow 2 * e) / &2)`) THEN
  REWRITE_TAC[REAL_LT_MIN] THEN ANTS_TAC THENL
   [ASM_SIMP_TAC[GSYM REAL_ABS_NZ; REAL_LT_DIV; REAL_OF_NUM_LT; ARITH] THEN
    MATCH_MP_TAC REAL_LT_DIV THEN REWRITE_TAC[REAL_OF_NUM_LT; ARITH] THEN
    ONCE_REWRITE_TAC[GSYM REAL_POW2_ABS] THEN
    ASM_SIMP_TAC[REAL_LT_MUL; GSYM REAL_ABS_NZ; REAL_POW_LT];
    ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:A` THEN
  MATCH_MP_TAC MONO_AND THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `b:A` THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  SIMP_TAC[REAL_LT_RDIV_EQ; REAL_OF_NUM_LT; ARITH] THEN STRIP_TAC THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP (REAL_ARITH
   `abs(x - l) * &2 < abs l ==> ~(x = &0)`)) THEN
  ASM_SIMP_TAC[REAL_SUB_INV; REAL_ABS_DIV; REAL_LT_LDIV_EQ;
               GSYM REAL_ABS_NZ; REAL_ENTIRE] THEN
  FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
   `abs(x - y) * &2 < b * c ==> c * b <= d * &2 ==> abs(y - x) < d`)) THEN
  ASM_SIMP_TAC[GSYM REAL_MUL_ASSOC; REAL_LE_LMUL_EQ] THEN
  ONCE_REWRITE_TAC[GSYM REAL_POW2_ABS] THEN ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  ASM_SIMP_TAC[REAL_ABS_MUL; REAL_POW_2; REAL_MUL_ASSOC; GSYM REAL_ABS_NZ;
               REAL_LE_RMUL_EQ] THEN
  ASM_SIMP_TAC[REAL_ARITH `abs(x - y) * &2 < abs y ==> abs y <= &2 * abs x`]);;


let CONTINUOUS_INV = 
prove
 (`!net f. (lift o f) continuous net /\ ~(f(netlimit net) = &0)
           ==> (lift o inv o f) continuous net`,

  REWRITE_TAC[continuous; LIM_INV; o_THM]);;


let CONTINUOUS_AT_WITHIN_INV = 
prove
 (`!f s a:real^N.
        (lift o f) continuous (at a within s) /\ ~(f a = &0)
        ==> (lift o inv o f) continuous (at a within s)`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `trivial_limit (at (a:real^N) within s)` THENL
   [ASM_REWRITE_TAC[continuous; LIM];
    ASM_SIMP_TAC[NETLIMIT_WITHIN; CONTINUOUS_INV]]);;


let CONTINUOUS_AT_INV = 
prove
 (`!f a. (lift o f) continuous at a /\ ~(f a = &0)
         ==> (lift o inv o f) continuous at a`,

  ONCE_REWRITE_TAC[GSYM WITHIN_UNIV] THEN
  REWRITE_TAC[CONTINUOUS_AT_WITHIN_INV]);;


let CONTINUOUS_ON_INV = 
prove
 (`!f s. (lift o f) continuous_on s /\ (!x. x IN s ==> ~(f x = &0))
         ==> (lift o inv o f) continuous_on s`,

(* ------------------------------------------------------------------------- *)
(* More preservation properties for pasted sets (Cartesian products).        *)
(* ------------------------------------------------------------------------- *)


let LIM_PASTECART = 
prove
 (`!net f:A->real^M g:A->real^N.
        (f --> a) net /\ (g --> b) net
        ==> ((\x. pastecart (f x) (g x)) --> pastecart a b) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[LIM] THEN
  ASM_CASES_TAC `trivial_limit(net:(A)net)` THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[AND_FORALL_THM] THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(MP_TAC o MATCH_MP NET_DILEMMA) THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN MATCH_MP_TAC MONO_AND THEN
  REWRITE_TAC[] THEN MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  REWRITE_TAC[dist; PASTECART_SUB] THEN
  MATCH_MP_TAC(REAL_ARITH
    `z <= x + y ==> x < e / &2 /\ y < e / &2 ==> z < e`) THEN
  REWRITE_TAC[NORM_PASTECART_LE]);;


let LIM_PASTECART_EQ = 
prove
 (`!net f:A->real^M g:A->real^N.
        ((\x. pastecart (f x) (g x)) --> pastecart a b) net <=>
        (f --> a) net /\ (g --> b) net`,

  REPEAT GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[LIM_PASTECART] THEN
  REPEAT STRIP_TAC THENL
   [FIRST_ASSUM(MP_TAC o ISPEC `fstcart:real^(M,N)finite_sum->real^M` o
        MATCH_MP (REWRITE_RULE[IMP_CONJ] LIM_LINEAR)) THEN
    REWRITE_TAC[LINEAR_FSTCART; FSTCART_PASTECART; ETA_AX];
    FIRST_ASSUM(MP_TAC o ISPEC `sndcart:real^(M,N)finite_sum->real^N` o
        MATCH_MP (REWRITE_RULE[IMP_CONJ] LIM_LINEAR)) THEN
    REWRITE_TAC[LINEAR_SNDCART; SNDCART_PASTECART; ETA_AX]]);;


let CONTINUOUS_PASTECART = 
prove
 (`!net f:A->real^M g:A->real^N.
        f continuous net /\ g continuous net
        ==> (\x. pastecart (f x) (g x)) continuous net`,

  REWRITE_TAC[continuous; LIM_PASTECART]);;


let CONTINUOUS_ON_PASTECART = 
prove
 (`!f:real^M->real^N g:real^M->real^P s.
        f continuous_on s /\ g continuous_on s
        ==> (\x. pastecart (f x) (g x)) continuous_on s`,


let CONNECTED_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        connected s /\ connected t
        ==> connected (s PCROSS t)`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[PCROSS; CONNECTED_IFF_CONNECTED_COMPONENT] THEN
  DISCH_TAC THEN REWRITE_TAC[FORALL_PASTECART; IN_ELIM_PASTECART_THM] THEN
  MAP_EVERY X_GEN_TAC [`x1:real^M`; `y1:real^N`; `x2:real^M`; `y2:real^N`] THEN
  STRIP_TAC THEN FIRST_X_ASSUM(CONJUNCTS_THEN2
   (MP_TAC o SPECL [`x1:real^M`; `x2:real^M`])
   (MP_TAC o SPECL [`y1:real^N`; `y2:real^N`])) THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM; connected_component] THEN
  X_GEN_TAC `c2:real^N->bool` THEN STRIP_TAC THEN
  X_GEN_TAC `c1:real^M->bool` THEN STRIP_TAC THEN
  EXISTS_TAC
   `IMAGE (\x:real^M. pastecart x y1) c1 UNION
    IMAGE (\y:real^N. pastecart x2 y) c2` THEN
  REWRITE_TAC[IN_UNION] THEN REPEAT CONJ_TAC THENL
   [MATCH_MP_TAC CONNECTED_UNION THEN
    ASM_SIMP_TAC[CONNECTED_CONTINUOUS_IMAGE; CONTINUOUS_ON_PASTECART;
                 CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID] THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_INTER; EXISTS_IN_IMAGE] THEN
    EXISTS_TAC `x2:real^M` THEN ASM SET_TAC[];
    REWRITE_TAC[SUBSET; IN_UNION; FORALL_AND_THM; FORALL_IN_IMAGE;
                TAUT `a \/ b ==> c <=> (a ==> c) /\ (b ==> c)`] THEN
    ASM SET_TAC[];
    ASM SET_TAC[];
    ASM SET_TAC[]]);;


let CONNECTED_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        connected (s PCROSS t) <=>
        s = {} \/ t = {} \/ connected s /\ connected t`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s:real^M->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  REWRITE_TAC[PCROSS_EMPTY; CONNECTED_EMPTY] THEN
  EQ_TAC THEN SIMP_TAC[CONNECTED_PCROSS] THEN
  REWRITE_TAC[PCROSS] THEN REPEAT STRIP_TAC THENL
   [SUBGOAL_THEN `connected (IMAGE fstcart
                     {pastecart (x:real^M) (y:real^N) | x IN s /\ y IN t})`
    MP_TAC THENL [MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE; ALL_TAC];
    SUBGOAL_THEN `connected (IMAGE sndcart
                     {pastecart (x:real^M) (y:real^N) | x IN s /\ y IN t})`
    MP_TAC THENL [MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE; ALL_TAC]] THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_ON; LINEAR_FSTCART; LINEAR_SNDCART] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_IMAGE; EXISTS_PASTECART; IN_ELIM_PASTECART_THM;
              FSTCART_PASTECART; SNDCART_PASTECART] THEN
  ASM SET_TAC[]);;


let CLOSURE_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        closure (s PCROSS t) = (closure s) PCROSS (closure t)`,

  REWRITE_TAC[EXTENSION; PCROSS; FORALL_PASTECART] THEN REPEAT GEN_TAC THEN
  REWRITE_TAC[CLOSURE_APPROACHABLE; EXISTS_PASTECART; FORALL_PASTECART] THEN
  REWRITE_TAC[IN_ELIM_PASTECART_THM; PASTECART_INJ] THEN
  REWRITE_TAC[FSTCART_PASTECART; SNDCART_PASTECART] THEN
  REWRITE_TAC[dist; PASTECART_SUB] THEN EQ_TAC THENL
   [MESON_TAC[NORM_LE_PASTECART; REAL_LET_TRANS]; DISCH_TAC] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(CONJUNCTS_THEN (MP_TAC o SPEC `e / &2`)) THEN
  ASM_MESON_TAC[REAL_HALF; NORM_PASTECART_LE; REAL_ARITH
    `z <= x + y /\ x < e / &2 /\ y < e / &2 ==> z < e`]);;


let LIMPT_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool x y.
        x limit_point_of s /\ y limit_point_of t
        ==> (pastecart x y) limit_point_of (s PCROSS t)`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[PCROSS; LIMPT_APPROACHABLE; EXISTS_PASTECART] THEN
  REWRITE_TAC[IN_ELIM_PASTECART_THM; PASTECART_INJ; dist; PASTECART_SUB] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(CONJUNCTS_THEN (MP_TAC o SPEC `e / &2`)) THEN
  ASM_MESON_TAC[REAL_HALF; NORM_PASTECART_LE; REAL_ARITH
    `z <= x + y /\ x < e / &2 /\ y < e / &2 ==> z < e`]);;


let CLOSED_IN_PCROSS = 
prove
 (`!s:real^M->bool s' t:real^N->bool t'.
        closed_in (subtopology euclidean s) s' /\
        closed_in (subtopology euclidean t) t'
        ==> closed_in (subtopology euclidean (s PCROSS t)) (s' PCROSS t')`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `s'':real^M->bool` STRIP_ASSUME_TAC)
   (X_CHOOSE_THEN `t'':real^N->bool` STRIP_ASSUME_TAC)) THEN
  EXISTS_TAC `(s'':real^M->bool) PCROSS (t'':real^N->bool)` THEN
  ASM_SIMP_TAC[CLOSED_PCROSS; EXTENSION; FORALL_PASTECART] THEN
  REWRITE_TAC[IN_INTER; PASTECART_IN_PCROSS] THEN ASM SET_TAC[]);;


let CLOSED_IN_PCROSS_EQ = 
prove
 (`!s s':real^M->bool t t':real^N->bool.
        closed_in (subtopology euclidean (s PCROSS t)) (s' PCROSS t') <=>
        s' = {} \/ t' = {} \/
        closed_in (subtopology euclidean s) s' /\
        closed_in (subtopology euclidean t) t'`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s':real^M->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; CLOSED_IN_EMPTY] THEN
  ASM_CASES_TAC `t':real^N->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; CLOSED_IN_EMPTY] THEN
  EQ_TAC THEN REWRITE_TAC[CLOSED_IN_PCROSS] THEN
  ASM_REWRITE_TAC[CLOSED_IN_INTER_CLOSURE; CLOSURE_PCROSS; INTER_PCROSS;
                  PCROSS_EQ; PCROSS_EQ_EMPTY]);;


let FRONTIER_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        frontier(s PCROSS t) = frontier s PCROSS closure t UNION
                               closure s PCROSS frontier t`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[frontier; CLOSURE_PCROSS; INTERIOR_PCROSS; PCROSS_DIFF] THEN
  REWRITE_TAC[EXTENSION; FORALL_PASTECART; IN_DIFF; IN_UNION;
              PASTECART_IN_PCROSS] THEN
  ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Hence some useful properties follow quite easily.                         *)
(* ------------------------------------------------------------------------- *)


let CONNECTED_SCALING = 
prove
 (`!s:real^N->bool c. connected s ==> connected (IMAGE (\x. c % x) s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_AT THEN
  REWRITE_TAC[linear] THEN CONJ_TAC THEN VECTOR_ARITH_TAC);;


let CONNECTED_NEGATIONS = 
prove
 (`!s:real^N->bool. connected s ==> connected (IMAGE (--) s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_AT THEN
  REWRITE_TAC[linear] THEN CONJ_TAC THEN VECTOR_ARITH_TAC);;


let CONNECTED_SUMS = 
prove
 (`!s t:real^N->bool.
        connected s /\ connected t ==> connected {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP CONNECTED_PCROSS) THEN
  DISCH_THEN(MP_TAC o ISPEC
   `\z. (fstcart z + sndcart z:real^N)` o
    MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT] CONNECTED_CONTINUOUS_IMAGE)) THEN
  SIMP_TAC[CONTINUOUS_ON_ADD; LINEAR_CONTINUOUS_ON; LINEAR_FSTCART;
           LINEAR_SNDCART; PCROSS] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_IMAGE; IN_ELIM_THM; EXISTS_PASTECART] THEN
  REWRITE_TAC[PASTECART_INJ; FSTCART_PASTECART; SNDCART_PASTECART] THEN
  MESON_TAC[]);;


let COMPACT_SCALING = 
prove
 (`!s:real^N->bool c. compact s ==> compact (IMAGE (\x. c % x) s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_AT THEN
  REWRITE_TAC[linear] THEN CONJ_TAC THEN VECTOR_ARITH_TAC);;


let COMPACT_NEGATIONS = 
prove
 (`!s:real^N->bool. compact s ==> compact (IMAGE (--) s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_AT THEN
  REWRITE_TAC[linear] THEN CONJ_TAC THEN VECTOR_ARITH_TAC);;


let COMPACT_SUMS = 
prove
 (`!s:real^N->bool t.
        compact s /\ compact t ==> compact {x + y | x IN s /\ y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `{x + y | x IN s /\ y IN t} =
                IMAGE (\z. fstcart z + sndcart z :real^N) (s PCROSS t)`
  SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE; PCROSS] THEN
    GEN_TAC THEN EQ_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_MESON_TAC[FSTCART_PASTECART; SNDCART_PASTECART; PASTECART_FST_SND];
    ALL_TAC] THEN
  MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
  ASM_SIMP_TAC[COMPACT_PCROSS] THEN
  MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_AT THEN
  REWRITE_TAC[linear; FSTCART_ADD; FSTCART_CMUL; SNDCART_ADD;
              SNDCART_CMUL] THEN
  CONJ_TAC THEN VECTOR_ARITH_TAC);;


let COMPACT_DIFFERENCES = 
prove
 (`!s:real^N->bool t.
        compact s /\ compact t ==> compact {x - y | x IN s /\ y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `{x - y | x:real^N IN s /\ y IN t} =
                {x + y | x IN s /\ y IN (IMAGE (--) t)}`
    (fun th -> ASM_SIMP_TAC[th; COMPACT_SUMS; COMPACT_NEGATIONS]) THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE] THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH `(x:real^N = --y) <=> (y = --x)`] THEN
  SIMP_TAC[VECTOR_SUB; GSYM CONJ_ASSOC; UNWIND_THM2] THEN
  MESON_TAC[VECTOR_NEG_NEG]);;


let COMPACT_AFFINITY = 
prove
 (`!s a:real^N c.
        compact s ==> compact (IMAGE (\x. a + c % x) s)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `(\x:real^N. a + c % x) = (\x. a + x) o (\x. c % x)`
  SUBST1_TAC THENL [REWRITE_TAC[o_DEF]; ALL_TAC] THEN
  ASM_SIMP_TAC[IMAGE_o; COMPACT_TRANSLATION; COMPACT_SCALING]);;

(* ------------------------------------------------------------------------- *)
(* Hence we get the following.                                               *)
(* ------------------------------------------------------------------------- *)


let COMPACT_SUP_MAXDISTANCE = 
prove
 (`!s:real^N->bool.
        compact s /\ ~(s = {})
        ==> ?x y. x IN s /\ y IN s /\
                  !u v. u IN s /\ v IN s ==> norm(u - v) <= norm(x - y)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`{x - y:real^N | x IN s /\ y IN s}`; `vec 0:real^N`]
                DISTANCE_ATTAINS_SUP) THEN
  ANTS_TAC THENL
   [ASM_SIMP_TAC[COMPACT_DIFFERENCES] THEN
    REWRITE_TAC[EXTENSION; IN_ELIM_THM; NOT_IN_EMPTY] THEN
    ASM_MESON_TAC[MEMBER_NOT_EMPTY];
    REWRITE_TAC[IN_ELIM_THM; dist; VECTOR_SUB_RZERO; VECTOR_SUB_LZERO;
                NORM_NEG] THEN
    MESON_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* We can state this in terms of diameter of a set.                          *)
(* ------------------------------------------------------------------------- *)


let diameter = new_definition
  `diameter s =
        if s = {} then &0
        else sup {norm(x - y) | x IN s /\ y IN s}`;;


let DIAMETER_BOUNDED = 
prove
 (`!s. bounded s
       ==> (!x:real^N y. x IN s /\ y IN s ==> norm(x - y) <= diameter s) /\
           (!d. &0 <= d /\ d < diameter s
                ==> ?x y. x IN s /\ y IN s /\ norm(x - y) > d)`,

  GEN_TAC THEN DISCH_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[diameter; NOT_IN_EMPTY; REAL_LET_ANTISYM] THEN
  MP_TAC(SPEC `{norm(x - y:real^N) | x IN s /\ y IN s}` SUP) THEN
  ABBREV_TAC `b = sup {norm(x - y:real^N) | x IN s /\ y IN s}` THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN
  REWRITE_TAC[NOT_IN_EMPTY; real_gt] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ASM_MESON_TAC[MEMBER_NOT_EMPTY]; ALL_TAC];
    MESON_TAC[REAL_NOT_LE]] THEN
  SIMP_TAC[VECTOR_SUB; LEFT_IMP_EXISTS_THM] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [bounded]) THEN
  MESON_TAC[REAL_ARITH `x <= y + z /\ y <= b /\ z<= b ==> x <= b + b`;
            NORM_TRIANGLE; NORM_NEG]);;


let DIAMETER_BOUNDED_BOUND = 
prove
 (`!s x y. bounded s /\ x IN s /\ y IN s ==> norm(x - y) <= diameter s`,

  MESON_TAC[DIAMETER_BOUNDED]);;


let DIAMETER_COMPACT_ATTAINED = 
prove
 (`!s:real^N->bool.
        compact s /\ ~(s = {})
        ==> ?x y. x IN s /\ y IN s /\ (norm(x - y) = diameter s)`,

  GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP COMPACT_SUP_MAXDISTANCE) THEN
  REPEAT(MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC) THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  MP_TAC(SPEC `s:real^N->bool` DIAMETER_BOUNDED) THEN
  RULE_ASSUM_TAC(REWRITE_RULE[COMPACT_EQ_BOUNDED_CLOSED]) THEN
  ASM_REWRITE_TAC[real_gt] THEN STRIP_TAC THEN
  REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN
  ASM_MESON_TAC[NORM_POS_LE; REAL_NOT_LT]);;


let DIAMETER_TRANSLATION = 
prove
 (`!a s. diameter (IMAGE (\x. a + x) s) = diameter s`,

  REWRITE_TAC[diameter] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [DIAMETER_TRANSLATION];;


let DIAMETER_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x. norm(f x) = norm x)
        ==> diameter(IMAGE f s) = diameter s`,

  REWRITE_TAC[diameter] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[diameter; IMAGE_EQ_EMPTY] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN
  REWRITE_TAC[GSYM CONJ_ASSOC; RIGHT_EXISTS_AND_THM; EXISTS_IN_IMAGE] THEN
  ASM_MESON_TAC[LINEAR_SUB]);;

add_linear_invariants [DIAMETER_LINEAR_IMAGE];;


let DIAMETER_EMPTY = 
prove
 (`diameter {} = &0`,

  REWRITE_TAC[diameter]);;


let DIAMETER_SING = 
prove
 (`!a. diameter {a} = &0`,

  REWRITE_TAC[diameter; NOT_INSERT_EMPTY; IN_SING] THEN
  REWRITE_TAC[SET_RULE `{f x y | x = a /\ y = a} = {f a a }`] THEN
  REWRITE_TAC[SUP_SING; VECTOR_SUB_REFL; NORM_0]);;


let DIAMETER_POS_LE = 
prove
 (`!s:real^N->bool. bounded s ==> &0 <= diameter s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[diameter] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[REAL_LE_REFL] THEN
  MP_TAC(SPEC `{norm(x - y:real^N) | x IN s /\ y IN s}` SUP) THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    FIRST_X_ASSUM(X_CHOOSE_TAC `B:real` o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
    EXISTS_TAC `&2 * B` THEN
    ASM_SIMP_TAC[NORM_ARITH
      `norm x <= B /\ norm y <= B ==> norm(x - y) <= &2 * B`];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    DISCH_THEN(X_CHOOSE_TAC `a:real^N`) THEN
    DISCH_THEN(MP_TAC o SPECL [`a:real^N`; `a:real^N`] o CONJUNCT1) THEN
    ASM_REWRITE_TAC[VECTOR_SUB_REFL; NORM_0]]);;


let DIAMETER_SUBSET = 
prove
 (`!s t:real^N->bool. s SUBSET t /\ bounded t ==> diameter s <= diameter t`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_SIMP_TAC[DIAMETER_EMPTY; DIAMETER_POS_LE] THEN
  ASM_REWRITE_TAC[diameter] THEN
  COND_CASES_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC REAL_SUP_LE_SUBSET THEN
  REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN
  FIRST_X_ASSUM(X_CHOOSE_TAC `B:real` o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
  EXISTS_TAC `&2 * B` THEN
  ASM_SIMP_TAC[NORM_ARITH
    `norm x <= B /\ norm y <= B ==> norm(x - y) <= &2 * B`]);;


let DIAMETER_CLOSURE = 
prove
 (`!s:real^N->bool. bounded s ==> diameter(closure s) = diameter s`,

  REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[DIAMETER_SUBSET; BOUNDED_CLOSURE; CLOSURE_SUBSET] THEN
  REWRITE_TAC[GSYM REAL_NOT_LT] THEN ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN
  DISCH_TAC THEN MP_TAC(ISPEC `closure s:real^N->bool` DIAMETER_BOUNDED) THEN
  ABBREV_TAC `d = diameter(closure s) - diameter(s:real^N->bool)` THEN
  ASM_SIMP_TAC[BOUNDED_CLOSURE] THEN DISCH_THEN(MP_TAC o
    SPEC `diameter(closure(s:real^N->bool)) - d / &2` o CONJUNCT2) THEN
  REWRITE_TAC[NOT_IMP; GSYM CONJ_ASSOC; NOT_EXISTS_THM] THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP DIAMETER_POS_LE) THEN
  REPEAT(CONJ_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC]) THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `y:real^N`] THEN
  REWRITE_TAC[CLOSURE_APPROACHABLE; CONJ_ASSOC; AND_FORALL_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 (MP_TAC o SPEC `d / &4`) ASSUME_TAC) THEN
  ASM_REWRITE_TAC[REAL_ARITH `&0 < d / &4 <=> &0 < d`] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `u:real^N` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC))
   (X_CHOOSE_THEN `v:real^N` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC))) THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP DIAMETER_BOUNDED) THEN
  DISCH_THEN(MP_TAC o SPECL [`u:real^N`; `v:real^N`] o CONJUNCT1) THEN
  ASM_REWRITE_TAC[] THEN REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC);;


let DIAMETER_SUBSET_CBALL_NONEMPTY = 
prove
 (`!s:real^N->bool.
       bounded s /\ ~(s = {}) ==> ?z. z IN s /\ s SUBSET cball(z,diameter s)`,

   REPEAT STRIP_TAC THEN
   FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
   MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN
   DISCH_TAC THEN ASM_REWRITE_TAC[SUBSET] THEN X_GEN_TAC `b:real^N` THEN
   DISCH_TAC THEN REWRITE_TAC[IN_CBALL; dist] THEN
   ASM_MESON_TAC[DIAMETER_BOUNDED]);;


let DIAMETER_SUBSET_CBALL = 
prove
 (`!s:real^N->bool. bounded s ==> ?z. s SUBSET cball(z,diameter s)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_MESON_TAC[DIAMETER_SUBSET_CBALL_NONEMPTY; EMPTY_SUBSET]);;


let DIAMETER_EQ_0 = 
prove
 (`!s:real^N->bool.
        bounded s ==> (diameter s = &0 <=> s = {} \/ ?a. s = {a})`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN STRIP_TAC THEN
  ASM_REWRITE_TAC[DIAMETER_EMPTY; DIAMETER_SING] THEN
  REWRITE_TAC[SET_RULE
   `s = {} \/ (?a. s = {a}) <=> !a b. a IN s /\ b IN s ==> a = b`] THEN
  MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`] THEN STRIP_TAC THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `a:real^N`; `b:real^N`]
        DIAMETER_BOUNDED_BOUND) THEN
  ASM_REWRITE_TAC[] THEN NORM_ARITH_TAC);;


let DIAMETER_LE = 
prove
 (`!s:real^N->bool.
        (~(s = {}) \/ &0 <= d) /\
        (!x y. x IN s /\ y IN s ==> norm(x - y) <= d) ==> diameter s <= d`,

  GEN_TAC THEN REWRITE_TAC[diameter] THEN
  COND_CASES_TAC THEN ASM_SIMP_TAC[] THEN
  STRIP_TAC THEN MATCH_MP_TAC REAL_SUP_LE THEN
  CONJ_TAC THENL [ASM SET_TAC[]; ASM_SIMP_TAC[FORALL_IN_GSPEC]]);;


let DIAMETER_CBALL = 
prove
 (`!a:real^N r. diameter(cball(a,r)) = if r < &0 then &0 else &2 * r`,

  REPEAT GEN_TAC THEN COND_CASES_TAC THENL
   [ASM_MESON_TAC[CBALL_EQ_EMPTY; DIAMETER_EMPTY]; ALL_TAC] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[REAL_NOT_LT]) THEN
  REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN CONJ_TAC THENL
   [MATCH_MP_TAC DIAMETER_LE THEN
    ASM_SIMP_TAC[CBALL_EQ_EMPTY; REAL_LE_MUL; REAL_POS; REAL_NOT_LT] THEN
    REWRITE_TAC[IN_CBALL] THEN NORM_ARITH_TAC;
    MATCH_MP_TAC REAL_LE_TRANS THEN
    EXISTS_TAC `norm((a + r % basis 1) - (a - r % basis 1):real^N)` THEN
    CONJ_TAC THENL
     [REWRITE_TAC[VECTOR_ARITH `(a + r % b) - (a - r % b:real^N) =
                                (&2 * r) % b`] THEN
      SIMP_TAC[NORM_MUL; NORM_BASIS; DIMINDEX_GE_1; LE_REFL] THEN
      ASM_REAL_ARITH_TAC;
      MATCH_MP_TAC DIAMETER_BOUNDED_BOUND THEN
      REWRITE_TAC[BOUNDED_CBALL; IN_CBALL] THEN
      REWRITE_TAC[NORM_ARITH
       `dist(a:real^N,a + b) = norm b /\ dist(a,a - b) = norm b`] THEN
      SIMP_TAC[NORM_MUL; NORM_BASIS; DIMINDEX_GE_1; LE_REFL] THEN
      ASM_REAL_ARITH_TAC]]);;


let DIAMETER_BALL = 
prove
 (`!a:real^N r. diameter(ball(a,r)) = if r < &0 then &0 else &2 * r`,

  REPEAT GEN_TAC THEN COND_CASES_TAC THENL
   [ASM_SIMP_TAC[BALL_EMPTY; REAL_LT_IMP_LE; DIAMETER_EMPTY]; ALL_TAC] THEN
  ASM_CASES_TAC `r = &0` THEN
  ASM_SIMP_TAC[BALL_EMPTY; REAL_LE_REFL; DIAMETER_EMPTY; REAL_MUL_RZERO] THEN
  MATCH_MP_TAC EQ_TRANS THEN
  EXISTS_TAC `diameter(cball(a:real^N,r))` THEN CONJ_TAC THENL
   [SUBGOAL_THEN `&0 < r` ASSUME_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
    ASM_SIMP_TAC[GSYM CLOSURE_BALL; DIAMETER_CLOSURE; BOUNDED_BALL];
    ASM_SIMP_TAC[DIAMETER_CBALL]]);;


let DIAMETER_SUMS = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t
        ==> diameter {x + y | x IN s /\ y IN t} <= diameter s + diameter t`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_SIMP_TAC[NOT_IN_EMPTY; SET_RULE `{f x y |x,y| F} = {}`;
               DIAMETER_EMPTY; REAL_ADD_LID; DIAMETER_POS_LE] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN
  ASM_SIMP_TAC[NOT_IN_EMPTY; SET_RULE `{f x y |x,y| F} = {}`;
               DIAMETER_EMPTY; REAL_ADD_RID; DIAMETER_POS_LE] THEN
  MATCH_MP_TAC DIAMETER_LE THEN CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  REWRITE_TAC[RIGHT_FORALL_IMP_THM; IMP_CONJ; FORALL_IN_GSPEC] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC(NORM_ARITH
   `norm(x - x') <= s /\ norm(y - y') <= t
    ==> norm((x + y) - (x' + y'):real^N) <= s + t`) THEN
  ASM_SIMP_TAC[DIAMETER_BOUNDED_BOUND]);;


let LEBESGUE_COVERING_LEMMA = 
prove
 (`!s:real^N->bool c.
        compact s /\ ~(c = {}) /\ s SUBSET UNIONS c /\ (!b. b IN c ==> open b)
        ==> ?d. &0 < d /\
                !t. t SUBSET s /\ diameter t <= d
                    ==> ?b. b IN c /\ t SUBSET b`,

  REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP HEINE_BOREL_LEMMA) THEN
  DISCH_THEN(MP_TAC o SPEC `c:(real^N->bool)->bool`) THEN ASM_SIMP_TAC[] THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `e:real` THEN
  STRIP_TAC THEN EXISTS_TAC `e / &2` THEN ASM_REWRITE_TAC[REAL_HALF] THEN
  X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPEC `t:real^N->bool` DIAMETER_SUBSET_CBALL_NONEMPTY) THEN
  ANTS_TAC THENL
   [ASM_MESON_TAC[BOUNDED_SUBSET; COMPACT_IMP_BOUNDED]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `x:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; MATCH_MP_TAC MONO_EXISTS] THEN
  X_GEN_TAC `b:real^N->bool` THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC SUBSET_TRANS THEN
  EXISTS_TAC `cball(x:real^N,diameter(t:real^N->bool))` THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC SUBSET_TRANS THEN
  EXISTS_TAC `ball(x:real^N,e)` THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[SUBSET; IN_CBALL; IN_BALL] THEN
  MAP_EVERY UNDISCH_TAC [`&0 < e`; `diameter(t:real^N->bool) <= e / &2`] THEN
  NORM_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Related results with closure as the conclusion.                           *)
(* ------------------------------------------------------------------------- *)


let CLOSED_SCALING = 
prove
 (`!s:real^N->bool c. closed s ==> closed (IMAGE (\x. c % x) s)`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s :real^N->bool = {}` THEN
  ASM_REWRITE_TAC[CLOSED_EMPTY; IMAGE_CLAUSES] THEN
  ASM_CASES_TAC `c = &0` THENL
   [SUBGOAL_THEN `IMAGE (\x:real^N. c % x) s = {(vec 0)}`
     (fun th -> REWRITE_TAC[th; CLOSED_SING]) THEN
    ASM_REWRITE_TAC[EXTENSION; IN_IMAGE; IN_SING; VECTOR_MUL_LZERO] THEN
    ASM_MESON_TAC[MEMBER_NOT_EMPTY];
    ALL_TAC] THEN
  REWRITE_TAC[CLOSED_SEQUENTIAL_LIMITS; IN_IMAGE; SKOLEM_THM] THEN
  STRIP_TAC THEN X_GEN_TAC `x:num->real^N` THEN X_GEN_TAC `l:real^N` THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `y:num->real^N` MP_TAC) THEN
  REWRITE_TAC[FORALL_AND_THM] THEN STRIP_TAC THEN
  EXISTS_TAC `inv(c) % l :real^N` THEN
  ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_RINV; VECTOR_MUL_LID] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN EXISTS_TAC `\n:num. inv(c) % x n:real^N` THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THENL
   [ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; VECTOR_MUL_LID];
    MATCH_MP_TAC LIM_CMUL THEN
    FIRST_ASSUM(fun th -> REWRITE_TAC[SYM(SPEC_ALL th)]) THEN
    ASM_REWRITE_TAC[ETA_AX]]);;


let CLOSED_NEGATIONS = 
prove
 (`!s:real^N->bool. closed s ==> closed (IMAGE (--) s)`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `IMAGE (--) s = IMAGE (\x:real^N. --(&1) % x) s`
  SUBST1_TAC THEN SIMP_TAC[CLOSED_SCALING] THEN
  REWRITE_TAC[VECTOR_ARITH `--(&1) % x = --x`] THEN REWRITE_TAC[ETA_AX]);;


let COMPACT_CLOSED_SUMS = 
prove
 (`!s:real^N->bool t.
        compact s /\ closed t ==> closed {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[compact; IN_ELIM_THM; CLOSED_SEQUENTIAL_LIMITS] THEN
  STRIP_TAC THEN X_GEN_TAC `f:num->real^N` THEN X_GEN_TAC `l:real^N` THEN
  REWRITE_TAC[SKOLEM_THM; FORALL_AND_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `a:num->real^N` MP_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `b:num->real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o check(is_imp o concl) o SPEC `a:num->real^N`) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `la:real^N` (X_CHOOSE_THEN `sub:num->num`
        STRIP_ASSUME_TAC)) THEN
  MAP_EVERY EXISTS_TAC [`la:real^N`; `l - la:real^N`] THEN
  ASM_REWRITE_TAC[VECTOR_ARITH `a + (b - a) = b:real^N`] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  EXISTS_TAC `\n. (f o (sub:num->num)) n - (a o sub) n:real^N` THEN
  CONJ_TAC THENL [ASM_REWRITE_TAC[VECTOR_ADD_SUB; o_THM]; ALL_TAC] THEN
  MATCH_MP_TAC LIM_SUB THEN ASM_SIMP_TAC[LIM_SUBSEQUENCE; ETA_AX]);;


let CLOSED_COMPACT_SUMS = 
prove
 (`!s:real^N->bool t.
        closed s /\ compact t ==> closed {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN
  SUBGOAL_THEN `{x + y:real^N | x IN s /\ y IN t} = {y + x | y IN t /\ x IN s}`
  SUBST1_TAC THEN  SIMP_TAC[COMPACT_CLOSED_SUMS] THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN MESON_TAC[VECTOR_ADD_SYM]);;


let CLOSURE_SUMS = 
prove
 (`!s t:real^N->bool.
        bounded s \/ bounded t
        ==> closure {x + y | x IN s /\ y IN t} =
            {x + y | x IN closure s /\ y IN closure t}`,

  REWRITE_TAC[TAUT `p \/ q ==> r <=> (p ==> r) /\ (q ==> r)`] THEN
  REWRITE_TAC[FORALL_AND_THM] THEN
  GEN_REWRITE_TAC (RAND_CONV o ONCE_DEPTH_CONV) [SUMS_SYM] THEN
  MATCH_MP_TAC(TAUT `(p ==> q) /\ p ==> p /\ q`) THEN
  SIMP_TAC[] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[EXTENSION; CLOSURE_SEQUENTIAL] THEN
  X_GEN_TAC `z:real^N` THEN REWRITE_TAC[IN_ELIM_THM] THEN EQ_TAC THENL
   [REWRITE_TAC[IN_ELIM_THM; IN_DELETE; SKOLEM_THM; LEFT_AND_EXISTS_THM] THEN
    REWRITE_TAC[FORALL_AND_THM] THEN
    ONCE_REWRITE_TAC[TAUT `(p /\ q) /\ r <=> q /\ p /\ r`] THEN
    ONCE_REWRITE_TAC[MESON[] `(?f x y. P f x y) <=> (?x y f. P f x y)`] THEN
    ONCE_REWRITE_TAC[GSYM FUN_EQ_THM] THEN
    REWRITE_TAC[ETA_AX; UNWIND_THM2] THEN
    REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`a:num->real^N`; `b:num->real^N`] THEN
    STRIP_TAC THEN
    MP_TAC(ISPEC `closure s:real^N->bool` compact) THEN
    ASM_REWRITE_TAC[COMPACT_CLOSURE] THEN
    DISCH_THEN(MP_TAC o SPEC `a:num->real^N`) THEN
    ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET; LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`u:real^N`; `r:num->num`] THEN STRIP_TAC THEN
    EXISTS_TAC `z - u:real^N` THEN
    EXISTS_TAC `(a:num->real^N) o (r:num->num)` THEN EXISTS_TAC `u:real^N` THEN
    ASM_REWRITE_TAC[o_THM] THEN
    CONJ_TAC THENL [ALL_TAC; VECTOR_ARITH_TAC] THEN
    EXISTS_TAC `(\n. ((\n. a n + b n) o (r:num->num)) n - (a o r) n)
                :num->real^N` THEN
    CONJ_TAC THENL
     [ASM_REWRITE_TAC[o_DEF; VECTOR_ARITH `(a + b) - a:real^N = b`];
      MATCH_MP_TAC LIM_SUB THEN ASM_REWRITE_TAC[ETA_AX] THEN
      MATCH_MP_TAC LIM_SUBSEQUENCE THEN ASM_REWRITE_TAC[]];
    REWRITE_TAC[LEFT_AND_EXISTS_THM] THEN
    REWRITE_TAC[LEFT_IMP_EXISTS_THM; LEFT_AND_EXISTS_THM;
                RIGHT_AND_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC
     [`x:real^N`; `y:real^N`; `a:num->real^N`; `b:num->real^N`] THEN
    STRIP_TAC THEN EXISTS_TAC `(\n. a n + b n):num->real^N` THEN
    ASM_SIMP_TAC[LIM_ADD] THEN ASM_MESON_TAC[]]);;


let COMPACT_CLOSED_DIFFERENCES = 
prove
 (`!s:real^N->bool t.
        compact s /\ closed t ==> closed {x - y | x IN s /\ y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `{x - y | x:real^N IN s /\ y IN t} =
                {x + y | x IN s /\ y IN (IMAGE (--) t)}`
    (fun th -> ASM_SIMP_TAC[th; COMPACT_CLOSED_SUMS; CLOSED_NEGATIONS]) THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE] THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH `(x:real^N = --y) <=> (y = --x)`] THEN
  SIMP_TAC[VECTOR_SUB; GSYM CONJ_ASSOC; UNWIND_THM2] THEN
  MESON_TAC[VECTOR_NEG_NEG]);;


let CLOSED_COMPACT_DIFFERENCES = 
prove
 (`!s:real^N->bool t.
        closed s /\ compact t ==> closed {x - y | x IN s /\ y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `{x - y | x:real^N IN s /\ y IN t} =
                {x + y | x IN s /\ y IN (IMAGE (--) t)}`
    (fun th -> ASM_SIMP_TAC[th; CLOSED_COMPACT_SUMS; COMPACT_NEGATIONS]) THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_IMAGE] THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH `(x:real^N = --y) <=> (y = --x)`] THEN
  SIMP_TAC[VECTOR_SUB; GSYM CONJ_ASSOC; UNWIND_THM2] THEN
  MESON_TAC[VECTOR_NEG_NEG]);;


let CLOSED_TRANSLATION_EQ = 
prove
 (`!a s. closed (IMAGE (\x:real^N. a + x) s) <=> closed s`,

  REWRITE_TAC[closed] THEN GEOM_TRANSLATE_TAC[]);;


let CLOSED_TRANSLATION = 
prove
 (`!s a:real^N. closed s ==> closed (IMAGE (\x. a + x) s)`,

  REWRITE_TAC[CLOSED_TRANSLATION_EQ]);;

add_translation_invariants [CLOSED_TRANSLATION_EQ];;


let COMPLETE_TRANSLATION_EQ = 
prove
 (`!a s. complete(IMAGE (\x:real^N. a + x) s) <=> complete s`,

add_translation_invariants [COMPLETE_TRANSLATION_EQ];;


let TRANSLATION_UNIV = 
prove
 (`!a. IMAGE (\x. a + x) (:real^N) = (:real^N)`,

  CONV_TAC(ONCE_DEPTH_CONV SYM_CONV) THEN GEOM_TRANSLATE_TAC[]);;


let TRANSLATION_DIFF = 
prove
 (`!s t:real^N->bool.
        IMAGE (\x. a + x) (s DIFF t) =
        (IMAGE (\x. a + x) s) DIFF (IMAGE (\x. a + x) t)`,

  REWRITE_TAC[EXTENSION; IN_DIFF; IN_IMAGE] THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH `x:real^N = a + y <=> y = x - a`] THEN
  REWRITE_TAC[UNWIND_THM2]);;


let CLOSURE_TRANSLATION = 
prove
 (`!a s. closure(IMAGE (\x:real^N. a + x) s) = IMAGE (\x. a + x) (closure s)`,

  REWRITE_TAC[CLOSURE_INTERIOR] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [CLOSURE_TRANSLATION];;


let FRONTIER_TRANSLATION = 
prove
 (`!a s. frontier(IMAGE (\x:real^N. a + x) s) = IMAGE (\x. a + x) (frontier s)`,

  REWRITE_TAC[frontier] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [FRONTIER_TRANSLATION];;

(* ------------------------------------------------------------------------- *)
(* Separation between points and sets.                                       *)
(* ------------------------------------------------------------------------- *)


let SEPARATE_POINT_CLOSED = 
prove
 (`!s a:real^N.
        closed s /\ ~(a IN s)
        ==> ?d. &0 < d /\ !x. x IN s ==> d <= dist(a,x)`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [EXISTS_TAC `&1` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY; REAL_LT_01];
    ALL_TAC] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `a:real^N`] DISTANCE_ATTAINS_INF) THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `b:real^N` THEN
  STRIP_TAC THEN EXISTS_TAC `dist(a:real^N,b)` THEN
  ASM_MESON_TAC[DIST_POS_LT]);;


let SEPARATE_COMPACT_CLOSED = 
prove
 (`!s t:real^N->bool.
        compact s /\ closed t /\ s INTER t = {}
        ==> ?d. &0 < d /\ !x y. x IN s /\ y IN t ==> d <= dist(x,y)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`{x - y:real^N | x IN s /\ y IN t}`; `vec 0:real^N`]
                SEPARATE_POINT_CLOSED) THEN
  ASM_SIMP_TAC[COMPACT_CLOSED_DIFFERENCES; IN_ELIM_THM] THEN
  REWRITE_TAC[VECTOR_ARITH `vec 0 = x - y <=> x = y`] THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN SIMP_TAC[LEFT_IMP_EXISTS_THM] THEN
  MESON_TAC[NORM_ARITH `dist(vec 0,x - y) = dist(x,y)`]);;


let SEPARATE_CLOSED_COMPACT = 
prove
 (`!s t:real^N->bool.
        closed s /\ compact t /\ s INTER t = {}
        ==> ?d. &0 < d /\ !x y. x IN s /\ y IN t ==> d <= dist(x,y)`,

  ONCE_REWRITE_TAC[DIST_SYM; INTER_COMM] THEN
  MESON_TAC[SEPARATE_COMPACT_CLOSED]);;

(* ------------------------------------------------------------------------- *)
(* Representing sets as the union of a chain of compact sets.                *)
(* ------------------------------------------------------------------------- *)


let CLOSED_UNION_COMPACT_SUBSETS = 
prove
 (`!s. closed s
       ==> ?f:num->real^N->bool.
                (!n. compact(f n)) /\
                (!n. (f n) SUBSET s) /\
                (!n. (f n) SUBSET f(n + 1)) /\
                UNIONS {f n | n IN (:num)} = s /\
                (!k. compact k /\ k SUBSET s
                     ==> ?N. !n. n >= N ==> k SUBSET (f n))`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `\n. s INTER cball(vec 0:real^N,&n)` THEN
  ASM_SIMP_TAC[INTER_SUBSET; COMPACT_CBALL; CLOSED_INTER_COMPACT] THEN
  REPEAT CONJ_TAC THENL
   [GEN_TAC THEN MATCH_MP_TAC(SET_RULE
     `t SUBSET u ==> s INTER t SUBSET s INTER u`) THEN
    REWRITE_TAC[SUBSET_BALLS; DIST_REFL; GSYM REAL_OF_NUM_ADD] THEN
    REAL_ARITH_TAC;
    REWRITE_TAC[EXTENSION; UNIONS_GSPEC; IN_ELIM_THM; IN_UNIV; IN_INTER] THEN
    X_GEN_TAC `x:real^N` THEN REWRITE_TAC[IN_CBALL_0] THEN
    MESON_TAC[REAL_ARCH_SIMPLE];
    X_GEN_TAC `k:real^N->bool` THEN SIMP_TAC[SUBSET_INTER] THEN
    REPEAT STRIP_TAC THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP COMPACT_IMP_BOUNDED) THEN DISCH_THEN
     (MP_TAC o SPEC `vec 0:real^N` o MATCH_MP BOUNDED_SUBSET_CBALL) THEN
    DISCH_THEN(X_CHOOSE_THEN `r:real` STRIP_ASSUME_TAC) THEN
    MP_TAC(ISPEC `r:real` REAL_ARCH_SIMPLE) THEN MATCH_MP_TAC MONO_EXISTS THEN
    X_GEN_TAC `N:num` THEN REWRITE_TAC[GSYM REAL_OF_NUM_GE] THEN

    REPEAT STRIP_TAC THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        SUBSET_TRANS)) THEN
    REWRITE_TAC[SUBSET_BALLS; DIST_REFL] THEN ASM_REAL_ARITH_TAC]);;


let OPEN_UNION_COMPACT_SUBSETS = 
prove
 (`!s. open s
       ==> ?f:num->real^N->bool.
                (!n. compact(f n)) /\
                (!n. (f n) SUBSET s) /\
                (!n. (f n) SUBSET interior(f(n + 1))) /\
                UNIONS {f n | n IN (:num)} = s /\
                (!k. compact k /\ k SUBSET s
                     ==> ?N. !n. n >= N ==> k SUBSET (f n))`,

  GEN_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [DISCH_TAC THEN EXISTS_TAC `(\n. {}):num->real^N->bool` THEN
    ASM_SIMP_TAC[EMPTY_SUBSET; SUBSET_EMPTY; COMPACT_EMPTY] THEN
    REWRITE_TAC[EXTENSION; UNIONS_GSPEC; IN_ELIM_THM; NOT_IN_EMPTY];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    DISCH_THEN(X_CHOOSE_TAC `a:real^N`) THEN STRIP_TAC] THEN
  MATCH_MP_TAC(MESON[]
   `(!f. p1 f /\ p3 f /\ p4 f ==> p5 f) /\
    (?f. p1 f /\ p2 f /\ p3 f /\ (p2 f ==> p4 f))
    ==> ?f. p1 f /\ p2 f /\ p3 f /\ p4 f /\ p5 f`) THEN
  CONJ_TAC THENL
   [X_GEN_TAC `f:num->real^N->bool` THEN STRIP_TAC THEN
    FIRST_X_ASSUM(SUBST1_TAC o SYM) THEN
    X_GEN_TAC `k:real^N->bool` THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [COMPACT_EQ_HEINE_BOREL]) THEN
    DISCH_THEN(MP_TAC o SPEC `{interior(f n):real^N->bool | n IN (:num)}`) THEN
    REWRITE_TAC[FORALL_IN_GSPEC; OPEN_INTERIOR] THEN ANTS_TAC THENL
     [FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        SUBSET_TRANS)) THEN
      REWRITE_TAC[SUBSET; UNIONS_GSPEC; IN_ELIM_THM] THEN ASM SET_TAC[];
      ONCE_REWRITE_TAC[TAUT `p /\ q /\ r <=> q /\ p /\ r`] THEN
      REWRITE_TAC[SIMPLE_IMAGE; EXISTS_FINITE_SUBSET_IMAGE] THEN
      REWRITE_TAC[SUBSET_UNIV] THEN
      DISCH_THEN(X_CHOOSE_THEN `i:num->bool` STRIP_ASSUME_TAC) THEN
      FIRST_ASSUM(MP_TAC o SPEC `\n:num. n` o
        MATCH_MP UPPER_BOUND_FINITE_SET) THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
      REWRITE_TAC[GE] THEN DISCH_TAC THEN X_GEN_TAC `n:num` THEN DISCH_TAC THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        SUBSET_TRANS)) THEN
      REWRITE_TAC[UNIONS_SUBSET; FORALL_IN_IMAGE] THEN
      X_GEN_TAC `m:num` THEN DISCH_TAC THEN MATCH_MP_TAC SUBSET_TRANS THEN
      EXISTS_TAC `(f:num->real^N->bool) m` THEN
      REWRITE_TAC[INTERIOR_SUBSET] THEN
      SUBGOAL_THEN `!m n. m <= n ==> (f:num->real^N->bool) m SUBSET f n`
       (fun th -> ASM_MESON_TAC[th; LE_TRANS]) THEN
      MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN
      ASM_MESON_TAC[SUBSET; ADD1; INTERIOR_SUBSET]];
    EXISTS_TAC
     `\n. cball(a,&n) DIFF
         {x + e | x IN (:real^N) DIFF s /\ e IN ball(vec 0,inv(&n + &1))}` THEN
    REWRITE_TAC[] THEN REPEAT CONJ_TAC THENL
     [X_GEN_TAC `n:num` THEN MATCH_MP_TAC COMPACT_DIFF THEN
      SIMP_TAC[COMPACT_CBALL; OPEN_SUMS; OPEN_BALL];
      GEN_TAC THEN MATCH_MP_TAC(SET_RULE
       `(UNIV DIFF s) SUBSET t ==> c DIFF t SUBSET s`) THEN
      REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN
      X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
      MAP_EVERY EXISTS_TAC [`x:real^N`; `vec 0:real^N`] THEN
      ASM_REWRITE_TAC[VECTOR_ADD_RID; CENTRE_IN_BALL; REAL_LT_INV_EQ] THEN
      REAL_ARITH_TAC;
      GEN_TAC THEN REWRITE_TAC[INTERIOR_DIFF] THEN MATCH_MP_TAC(SET_RULE
       `s SUBSET s' /\ t' SUBSET t ==> (s DIFF t) SUBSET (s' DIFF t')`) THEN
      CONJ_TAC THENL
       [REWRITE_TAC[INTERIOR_CBALL; SUBSET; IN_BALL; IN_CBALL] THEN
        REWRITE_TAC[GSYM REAL_OF_NUM_ADD] THEN REAL_ARITH_TAC;
        MATCH_MP_TAC SUBSET_TRANS THEN
        EXISTS_TAC `{x + e | x IN (:real^N) DIFF s /\
                             e IN cball(vec 0,inv(&n + &2))}` THEN
        CONJ_TAC THENL
         [MATCH_MP_TAC CLOSURE_MINIMAL THEN
          ASM_SIMP_TAC[CLOSED_COMPACT_SUMS; COMPACT_CBALL;
                       GSYM OPEN_CLOSED] THEN
          MATCH_MP_TAC(SET_RULE
           `t SUBSET t'
            ==> {f x y | x IN s /\ y IN t} SUBSET
                {f x y | x IN s /\ y IN t'}`) THEN
          REWRITE_TAC[SUBSET; IN_BALL; IN_CBALL; GSYM REAL_OF_NUM_ADD] THEN
          REAL_ARITH_TAC;
          MATCH_MP_TAC(SET_RULE
           `t SUBSET t'
            ==> {f x y | x IN s /\ y IN t} SUBSET
                {f x y | x IN s /\ y IN t'}`) THEN
          REWRITE_TAC[SUBSET; IN_BALL; IN_CBALL; GSYM REAL_OF_NUM_ADD] THEN
          GEN_TAC THEN MATCH_MP_TAC(REAL_ARITH
           `a < b ==> x <= a ==> x < b`) THEN
          MATCH_MP_TAC REAL_LT_INV2 THEN REAL_ARITH_TAC]];
      DISCH_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
      ASM_REWRITE_TAC[UNIONS_SUBSET; FORALL_IN_GSPEC] THEN
      REWRITE_TAC[SUBSET; UNIONS_GSPEC; IN_UNIV; IN_ELIM_THM] THEN
      X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN REWRITE_TAC[IN_DIFF] THEN
      REWRITE_TAC[IN_ELIM_THM; IN_UNIV; IN_BALL_0] THEN
      REWRITE_TAC[VECTOR_ARITH `x:real^N = y + e <=> e = x - y`] THEN
      REWRITE_TAC[TAUT `(p /\ q) /\ r <=> r /\ p /\ q`; UNWIND_THM2] THEN
      REWRITE_TAC[MESON[] `~(?x. ~P x /\ Q x) <=> !x. Q x ==> P x`] THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_CONTAINS_BALL]) THEN
      DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
      ASM_REWRITE_TAC[SUBSET; IN_BALL; dist] THEN
      DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
      FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [REAL_ARCH_INV]) THEN
      DISCH_THEN(X_CHOOSE_THEN `N1:num` STRIP_ASSUME_TAC) THEN
      MP_TAC(ISPEC `norm(x - a:real^N)` REAL_ARCH_SIMPLE) THEN
      DISCH_THEN(X_CHOOSE_TAC `N2:num`) THEN EXISTS_TAC `N1 + N2:num` THEN
      CONJ_TAC THENL
       [REWRITE_TAC[IN_CBALL] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
        UNDISCH_TAC `norm(x - a:real^N) <= &N2` THEN
        REWRITE_TAC[dist; GSYM REAL_OF_NUM_ADD] THEN REAL_ARITH_TAC;
        REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
        SUBGOAL_THEN `inv(&(N1 + N2) + &1) <= inv(&N1)` MP_TAC THENL
         [MATCH_MP_TAC REAL_LE_INV2 THEN
          ASM_SIMP_TAC[REAL_OF_NUM_LT; LE_1] THEN
          REWRITE_TAC[GSYM REAL_OF_NUM_ADD] THEN REAL_ARITH_TAC;
          ASM_REAL_ARITH_TAC]]]]);;

(* ------------------------------------------------------------------------- *)
(* Closed-graph characterization of continuity.                              *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_CLOSED_GRAPH_GEN = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s SUBSET t
        ==> closed_in (subtopology euclidean (s PCROSS t))
                      {pastecart x (f x) | x IN s}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `{pastecart (x:real^M) (f x:real^N) | x IN s} =
    {z | z IN s PCROSS t /\ f(fstcart z) - sndcart z IN {vec 0}}`
  SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; FORALL_PASTECART; IN_ELIM_THM; IN_SING;
                PASTECART_IN_PCROSS; FSTCART_PASTECART; SNDCART_PASTECART;
                PASTECART_INJ; VECTOR_SUB_EQ] THEN
    ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE THEN
    REWRITE_TAC[CLOSED_SING] THEN MATCH_MP_TAC CONTINUOUS_ON_SUB THEN
    SIMP_TAC[GSYM o_DEF; LINEAR_CONTINUOUS_ON; LINEAR_SNDCART] THEN
    MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
    SIMP_TAC[LINEAR_CONTINUOUS_ON; LINEAR_FSTCART; IMAGE_FSTCART_PCROSS] THEN
    ASM_MESON_TAC[CONTINUOUS_ON_EMPTY]]);;


let CONTINUOUS_CLOSED_GRAPH_EQ = 
prove
 (`!f:real^M->real^N s t.
        compact t /\ IMAGE f s SUBSET t
        ==> (f continuous_on s <=>
             closed_in (subtopology euclidean (s PCROSS t))
                       {pastecart x (f x) | x IN s})`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN
  ASM_SIMP_TAC[CONTINUOUS_CLOSED_GRAPH_GEN] THEN DISCH_TAC THEN
  FIRST_ASSUM(fun th ->
   REWRITE_TAC[MATCH_MP CONTINUOUS_ON_CLOSED_GEN th]) THEN
  X_GEN_TAC `c:real^N->bool` THEN STRIP_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ (f:real^M->real^N) x IN c} =
    IMAGE fstcart ({pastecart x (f x) | x IN s} INTER
                   (s PCROSS c))`
  SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_IMAGE; IN_ELIM_THM; EXISTS_PASTECART;
                FSTCART_PASTECART; IN_INTER; IN_ELIM_PASTECART_THM;
                PASTECART_IN_PCROSS; PASTECART_INJ] THEN
    ASM SET_TAC[];
    MATCH_MP_TAC CLOSED_MAP_FSTCART THEN EXISTS_TAC `t:real^N->bool` THEN
    ASM_REWRITE_TAC[] THEN MATCH_MP_TAC CLOSED_IN_INTER THEN
    ASM_REWRITE_TAC[] THEN  MATCH_MP_TAC CLOSED_IN_PCROSS THEN
    ASM_REWRITE_TAC[CLOSED_IN_REFL]]);;


let CONTINUOUS_CLOSED_GRAPH = 
prove
 (`!f:real^M->real^N s.
        closed s /\ f continuous_on s ==> closed {pastecart x (f x) | x IN s}`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSED_IN_CLOSED_TRANS THEN
  EXISTS_TAC `(s:real^M->bool) PCROSS (:real^N)` THEN
  ASM_SIMP_TAC[CLOSED_PCROSS; CLOSED_UNIV] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_GRAPH_GEN THEN
  ASM_REWRITE_TAC[SUBSET_UNIV]);;


let CONTINUOUS_FROM_CLOSED_GRAPH = 
prove
 (`!f:real^M->real^N s t.
        compact t /\ IMAGE f s SUBSET t /\
        closed {pastecart x (f x) | x IN s}
        ==> f continuous_on s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CONJ_ASSOC] THEN
  DISCH_THEN(CONJUNCTS_THEN ASSUME_TAC) THEN
  FIRST_ASSUM(SUBST1_TAC o MATCH_MP CONTINUOUS_CLOSED_GRAPH_EQ) THEN
  MATCH_MP_TAC CLOSED_SUBSET THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_GSPEC; PASTECART_IN_PCROSS] THEN
  ASM SET_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* A cute way of denoting open and closed intervals using overloading.       *)
(* ------------------------------------------------------------------------- *)


let open_interval = new_definition
  `open_interval(a:real^N,b:real^N) =
        {x:real^N | !i. 1 <= i /\ i <= dimindex(:N)
                        ==> a$i < x$i /\ x$i < b$i}`;;


let closed_interval = new_definition
  `closed_interval(l:(real^N#real^N)list) =
         {x:real^N | !i. 1 <= i /\ i <= dimindex(:N)
                         ==> FST(HD l)$i <= x$i /\ x$i <= SND(HD l)$i}`;;

make_overloadable "interval" `:A`;;

overload_interface("interval",`open_interval`);;
overload_interface("interval",`closed_interval`);;


let interval = 
prove
 (`(interval (a,b) = {x:real^N | !i. 1 <= i /\ i <= dimindex(:N)
                                     ==> a$i < x$i /\ x$i < b$i}) /\
   (interval [a,b] = {x:real^N | !i. 1 <= i /\ i <= dimindex(:N)
                                     ==> a$i <= x$i /\ x$i <= b$i})`,

  REWRITE_TAC[open_interval; closed_interval; HD; FST; SND]);;


let IN_INTERVAL = 
prove
 (`(!x:real^N.
        x IN interval (a,b) <=>
                !i. 1 <= i /\ i <= dimindex(:N)
                    ==> a$i < x$i /\ x$i < b$i) /\
   (!x:real^N.
        x IN interval [a,b] <=>
                !i. 1 <= i /\ i <= dimindex(:N)
                    ==> a$i <= x$i /\ x$i <= b$i)`,

  REWRITE_TAC[interval; IN_ELIM_THM]);;


let IN_INTERVAL_REFLECT = 
prove
 (`(!a b x. (--x) IN interval[--b,--a] <=> x IN interval[a,b]) /\
   (!a b x. (--x) IN interval(--b,--a) <=> x IN interval(a,b))`,

  SIMP_TAC[IN_INTERVAL; REAL_LT_NEG2; REAL_LE_NEG2; VECTOR_NEG_COMPONENT] THEN
  MESON_TAC[]);;


let REFLECT_INTERVAL = 
prove
 (`(!a b:real^N. IMAGE (--) (interval[a,b]) = interval[--b,--a]) /\
   (!a b:real^N. IMAGE (--) (interval(a,b)) = interval(--b,--a))`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
  REWRITE_TAC[IN_INTERVAL_REFLECT] THEN MESON_TAC[VECTOR_NEG_NEG]);;


let INTERVAL_EQ_EMPTY = 
prove
 (`((interval [a:real^N,b] = {}) <=>
    ?i. 1 <= i /\ i <= dimindex(:N) /\ b$i < a$i) /\
   ((interval (a:real^N,b) = {}) <=>
    ?i. 1 <= i /\ i <= dimindex(:N) /\ b$i <= a$i)`,

  REWRITE_TAC[EXTENSION; IN_INTERVAL; NOT_IN_EMPTY] THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; GSYM CONJ_ASSOC] THEN
  CONJ_TAC THEN EQ_TAC THENL
   [MESON_TAC[REAL_LE_REFL; REAL_NOT_LE];
    MESON_TAC[REAL_LE_TRANS; REAL_NOT_LE];
    ALL_TAC;
    MESON_TAC[REAL_LT_TRANS; REAL_NOT_LT]] THEN
  SUBGOAL_THEN `!a b. ?c. a < b ==> a < c /\ c < b`
  (MP_TAC o REWRITE_RULE[SKOLEM_THM]) THENL
   [MESON_TAC[REAL_LT_BETWEEN]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_TAC `mid:real->real->real`) THEN
  DISCH_THEN(MP_TAC o SPEC
   `(lambda i. mid ((a:real^N)$i) ((b:real^N)$i)):real^N`) THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c <=> ~(a /\ b ==> ~c)`] THEN
  SIMP_TAC[LAMBDA_BETA] THEN ASM_MESON_TAC[REAL_NOT_LT]);;


let INTERVAL_NE_EMPTY = 
prove
 (`(~(interval [a:real^N,b] = {}) <=>
    !i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= b$i) /\
   (~(interval (a:real^N,b) = {}) <=>
    !i. 1 <= i /\ i <= dimindex(:N) ==> a$i < b$i)`,

  REWRITE_TAC[INTERVAL_EQ_EMPTY] THEN MESON_TAC[REAL_NOT_LE]);;


let SUBSET_INTERVAL_IMP = 
prove
 (`((!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i)
    ==> interval[c,d] SUBSET interval[a:real^N,b]) /\
   ((!i. 1 <= i /\ i <= dimindex(:N) ==> a$i < c$i /\ d$i < b$i)
    ==> interval[c,d] SUBSET interval(a:real^N,b)) /\
   ((!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i)
    ==> interval(c,d) SUBSET interval[a:real^N,b]) /\
   ((!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i)
    ==> interval(c,d) SUBSET interval(a:real^N,b))`,

  REWRITE_TAC[SUBSET; IN_INTERVAL] THEN REPEAT CONJ_TAC THEN
  DISCH_TAC THEN GEN_TAC THEN POP_ASSUM MP_TAC THEN
  REWRITE_TAC[IMP_IMP; AND_FORALL_THM] THEN MATCH_MP_TAC MONO_FORALL THEN
  GEN_TAC THEN DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN REAL_ARITH_TAC);;


let INTERVAL_SING = 
prove
 (`interval[a,a] = {a} /\ interval(a,a) = {}`,

  REWRITE_TAC[EXTENSION; IN_SING; NOT_IN_EMPTY; IN_INTERVAL] THEN
  REWRITE_TAC[REAL_LE_ANTISYM; REAL_LT_ANTISYM; CART_EQ; EQ_SYM_EQ] THEN
  MESON_TAC[DIMINDEX_GE_1; LE_REFL]);;


let SUBSET_INTERVAL = 
prove
 (`(interval[c,d] SUBSET interval[a:real^N,b] <=>
        (!i. 1 <= i /\ i <= dimindex(:N) ==> c$i <= d$i)
        ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i)) /\
   (interval[c,d] SUBSET interval(a:real^N,b) <=>
        (!i. 1 <= i /\ i <= dimindex(:N) ==> c$i <= d$i)
        ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> a$i < c$i /\ d$i < b$i)) /\
   (interval(c,d) SUBSET interval[a:real^N,b] <=>
        (!i. 1 <= i /\ i <= dimindex(:N) ==> c$i < d$i)
        ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i)) /\
   (interval(c,d) SUBSET interval(a:real^N,b) <=>
        (!i. 1 <= i /\ i <= dimindex(:N) ==> c$i < d$i)
        ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> a$i <= c$i /\ d$i <= b$i))`,

  
let lemma = prove
   (`(!x:real^N. (!i. 1 <= i /\ i <= dimindex(:N) ==> Q i (x$i))
                 ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> R i (x$i)))
     ==> (!i. 1 <= i /\ i <= dimindex(:N) ==> ?y. Q i y)
         ==> !i y. 1 <= i /\ i <= dimindex(:N) /\ Q i y ==> R i y`,
    DISCH_TAC THEN REWRITE_TAC[RIGHT_IMP_EXISTS_THM; SKOLEM_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `f:num->real` STRIP_ASSUME_TAC) THEN
    REPEAT STRIP_TAC THEN FIRST_X_ASSUM(MP_TAC o
     SPEC `(lambda j. if j = i then y else f j):real^N`) THEN
    SIMP_TAC[LAMBDA_BETA] THEN ASM_MESON_TAC[]) in
  REPEAT STRIP_TAC THEN
  (MATCH_MP_TAC(TAUT
    `(~q ==> p) /\ (q ==> (p <=> r)) ==> (p <=> q ==> r)`) THEN
   CONJ_TAC THENL
    [DISCH_TAC THEN MATCH_MP_TAC(SET_RULE `s = {} ==> s SUBSET t`) THEN
     REWRITE_TAC[INTERVAL_EQ_EMPTY] THEN ASM_MESON_TAC[REAL_NOT_LT];
     ALL_TAC] THEN
   DISCH_TAC THEN EQ_TAC THEN REWRITE_TAC[SUBSET_INTERVAL_IMP] THEN
   REWRITE_TAC[SUBSET; IN_INTERVAL] THEN
   DISCH_THEN(MP_TAC o MATCH_MP lemma) THEN ANTS_TAC THENL
    [ASM_MESON_TAC[REAL_LT_BETWEEN; REAL_LE_BETWEEN]; ALL_TAC] THEN
   MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `i:num` THEN
   DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN ASM_REWRITE_TAC[] THEN
   FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN
   ASM_REWRITE_TAC[] THEN POP_ASSUM_LIST(K ALL_TAC) THEN STRIP_TAC)
  THENL
   [ASM_MESON_TAC[REAL_LE_TRANS; REAL_LE_REFL];
    ASM_MESON_TAC[REAL_LE_TRANS; REAL_LE_REFL];
    ALL_TAC; ALL_TAC] THEN
  (REPEAT STRIP_TAC THENL
    [FIRST_X_ASSUM(MP_TAC o SPEC
      `((c:real^N)$i + min ((a:real^N)$i) ((d:real^N)$i)) / &2`) THEN
     POP_ASSUM MP_TAC THEN REAL_ARITH_TAC;
     FIRST_X_ASSUM(MP_TAC o SPEC
      `(max ((b:real^N)$i) ((c:real^N)$i) + (d:real^N)$i) / &2`) THEN
     POP_ASSUM MP_TAC THEN REAL_ARITH_TAC]));;


let DISJOINT_INTERVAL = 
prove
 (`!a b c d:real^N.
        (interval[a,b] INTER interval[c,d] = {} <=>
          ?i. 1 <= i /\ i <= dimindex(:N) /\
              (b$i < a$i \/ d$i < c$i \/ b$i < c$i \/ d$i < a$i)) /\
        (interval[a,b] INTER interval(c,d) = {} <=>
          ?i. 1 <= i /\ i <= dimindex(:N) /\
              (b$i < a$i \/ d$i <= c$i \/ b$i <= c$i \/ d$i <= a$i)) /\
        (interval(a,b) INTER interval[c,d] = {} <=>
          ?i. 1 <= i /\ i <= dimindex(:N) /\
              (b$i <= a$i \/ d$i < c$i \/ b$i <= c$i \/ d$i <= a$i)) /\
        (interval(a,b) INTER interval(c,d) = {} <=>
          ?i. 1 <= i /\ i <= dimindex(:N) /\
              (b$i <= a$i \/ d$i <= c$i \/ b$i <= c$i \/ d$i <= a$i))`,

  REWRITE_TAC[EXTENSION; IN_INTER; IN_INTERVAL; NOT_IN_EMPTY] THEN
  REWRITE_TAC[AND_FORALL_THM; NOT_FORALL_THM] THEN
  REWRITE_TAC[TAUT `~((p ==> q) /\ (p ==> r)) <=> p /\ (~q \/ ~r)`] THEN
  REWRITE_TAC[DE_MORGAN_THM] THEN REPEAT STRIP_TAC THEN
  (EQ_TAC THENL
    [DISCH_THEN(MP_TAC o SPEC
      `(lambda i. (max ((a:real^N)$i) ((c:real^N)$i) +
                   min ((b:real^N)$i) ((d:real^N)$i)) / &2):real^N`) THEN
     MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
     DISCH_THEN(CONJUNCTS_THEN2 STRIP_ASSUME_TAC MP_TAC) THEN
     ASM_SIMP_TAC[LAMBDA_BETA] THEN REAL_ARITH_TAC;
     DISCH_THEN(fun th -> GEN_TAC THEN MP_TAC th) THEN
     MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN SIMP_TAC[] THEN
     REAL_ARITH_TAC]));;


let ENDS_IN_INTERVAL = 
prove
 (`(!a b. a IN interval[a,b] <=> ~(interval[a,b] = {})) /\
   (!a b. b IN interval[a,b] <=> ~(interval[a,b] = {})) /\
   (!a b. ~(a IN interval(a,b))) /\
   (!a b. ~(b IN interval(a,b)))`,

  REWRITE_TAC[IN_INTERVAL; INTERVAL_NE_EMPTY] THEN
  REWRITE_TAC[REAL_LE_REFL; REAL_LT_REFL] THEN
  MESON_TAC[DIMINDEX_GE_1; LE_REFL]);;


let ENDS_IN_UNIT_INTERVAL = 
prove
 (`vec 0 IN interval[vec 0,vec 1] /\
   vec 1 IN interval[vec 0,vec 1] /\
   ~(vec 0 IN interval(vec 0,vec 1)) /\
   ~(vec 1 IN interval(vec 0,vec 1))`,

  REWRITE_TAC[ENDS_IN_INTERVAL; INTERVAL_NE_EMPTY; VEC_COMPONENT] THEN
  REWRITE_TAC[REAL_POS]);;


let INTER_INTERVAL = 
prove
 (`interval[a,b] INTER interval[c,d] =
        interval[(lambda i. max (a$i) (c$i)),(lambda i. min (b$i) (d$i))]`,

  REWRITE_TAC[EXTENSION; IN_INTER; IN_INTERVAL] THEN
  SIMP_TAC[LAMBDA_BETA; REAL_MAX_LE; REAL_LE_MIN] THEN MESON_TAC[]);;


let INTERVAL_OPEN_SUBSET_CLOSED = 
prove
 (`!a b. interval(a,b) SUBSET interval[a,b]`,

  REWRITE_TAC[SUBSET; IN_INTERVAL] THEN MESON_TAC[REAL_LT_IMP_LE]);;


let OPEN_INTERVAL_LEMMA = 
prove
 (`!a b x. a < x /\ x < b
           ==> ?d. &0 < d /\ !x'. abs(x' - x) < d ==> a < x' /\ x' < b`,

  REPEAT STRIP_TAC THEN
  EXISTS_TAC `min (x - a) (b - x)` THEN REWRITE_TAC[REAL_LT_MIN] THEN
  ASM_REAL_ARITH_TAC);;


let OPEN_INTERVAL = 
prove
 (`!a:real^N b. open(interval (a,b))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_def; interval; IN_ELIM_THM] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  SUBGOAL_THEN `!i. 1 <= i /\ i <= dimindex(:N)
                    ==> ?d. &0 < d /\
                            !x'. abs(x' - (x:real^N)$i) < d
                                 ==> (a:real^N)$i < x' /\ x' < (b:real^N)$i`
  MP_TAC THENL [ASM_SIMP_TAC[OPEN_INTERVAL_LEMMA]; ALL_TAC] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:num->real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `inf (IMAGE d (1..dimindex(:N)))` THEN
  SIMP_TAC[REAL_LT_INF_FINITE; FINITE_IMAGE; FINITE_NUMSEG;
           IMAGE_EQ_EMPTY; NOT_INSERT_EMPTY; NUMSEG_EMPTY;
           ARITH_RULE `n < 1 <=> (n = 0)`; DIMINDEX_NONZERO] THEN
  REWRITE_TAC[FORALL_IN_IMAGE; IN_NUMSEG; dist] THEN
  ASM_MESON_TAC[COMPONENT_LE_NORM; REAL_LET_TRANS; VECTOR_SUB_COMPONENT]);;


let CLOSED_INTERVAL = 
prove
 (`!a:real^N b. closed(interval [a,b])`,

  REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE; IN_INTERVAL] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN DISCH_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `(a:real^N)$i - (x:real^N)$i`);
    FIRST_X_ASSUM(MP_TAC o SPEC `(x:real^N)$i - (b:real^N)$i`)] THEN
  ASM_REWRITE_TAC[REAL_SUB_LT] THEN
  DISCH_THEN(X_CHOOSE_THEN `z:real^N` MP_TAC) THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[dist; REAL_NOT_LT] THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `abs((z - x :real^N)$i)` THEN
  ASM_SIMP_TAC[COMPONENT_LE_NORM] THEN
  ASM_SIMP_TAC[VECTOR_SUB_COMPONENT] THEN
  ASM_SIMP_TAC[REAL_ARITH `x < a /\ a <= z ==> a - x <= abs(z - x)`;
               REAL_ARITH `z <= b /\ b < x ==> x - b <= abs(z - x)`]);;


let INTERIOR_CLOSED_INTERVAL = 
prove
 (`!a:real^N b. interior(interval [a,b]) = interval (a,b)`,

  REPEAT GEN_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
   [ALL_TAC;
    MATCH_MP_TAC INTERIOR_MAXIMAL THEN
    REWRITE_TAC[INTERVAL_OPEN_SUBSET_CLOSED; OPEN_INTERVAL]] THEN
  REWRITE_TAC[interior; SUBSET; IN_INTERVAL; IN_ELIM_THM] THEN
  X_GEN_TAC `x:real^N` THEN
  DISCH_THEN(X_CHOOSE_THEN `s:real^N->bool` STRIP_ASSUME_TAC) THEN
  X_GEN_TAC `i:num` THEN STRIP_TAC THEN
  ASM_SIMP_TAC[REAL_LT_LE] THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [open_def]) THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THENL
   [(let t = `x - (e / &2) % basis i :real^N` in
     DISCH_THEN(MP_TAC o SPEC t) THEN FIRST_X_ASSUM(MP_TAC o SPEC t));
    (let t = `x + (e / &2) % basis i :real^N` in
     DISCH_THEN(MP_TAC o SPEC t) THEN FIRST_X_ASSUM(MP_TAC o SPEC t))] THEN
  REWRITE_TAC[dist; VECTOR_ADD_SUB; VECTOR_ARITH `x - y - x = --y:real^N`] THEN
  ASM_SIMP_TAC[NORM_MUL; NORM_BASIS; NORM_NEG; REAL_MUL_RID;
               REAL_ARITH `&0 < e ==> abs(e / &2) < e`] THEN
  MATCH_MP_TAC(TAUT `~b ==> (a ==> b) ==> ~a`) THEN
  REWRITE_TAC[NOT_FORALL_THM] THEN EXISTS_TAC `i:num` THEN
  ASM_SIMP_TAC[DE_MORGAN_THM; VECTOR_SUB_COMPONENT; VECTOR_ADD_COMPONENT] THENL
   [DISJ1_TAC THEN REWRITE_TAC[REAL_ARITH `a <= a - b <=> ~(&0 < b)`];
    DISJ2_TAC THEN REWRITE_TAC[REAL_ARITH `a + b <= a <=> ~(&0 < b)`]] THEN
  ASM_SIMP_TAC[VECTOR_MUL_COMPONENT; basis; LAMBDA_BETA; REAL_MUL_RID] THEN
  ASM_REWRITE_TAC[REAL_HALF]);;


let INTERIOR_INTERVAL = 
prove
 (`(!a b. interior(interval[a,b]) = interval(a,b)) /\
   (!a b. interior(interval(a,b)) = interval(a,b))`,


let BOUNDED_CLOSED_INTERVAL = 
prove
 (`!a b:real^N. bounded (interval [a,b])`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[bounded; interval] THEN
  EXISTS_TAC `sum(1..dimindex(:N))
                 (\i. abs((a:real^N)$i) + abs((b:real^N)$i))` THEN
  X_GEN_TAC `x:real^N` THEN REWRITE_TAC[IN_ELIM_THM] THEN
  STRIP_TAC THEN MATCH_MP_TAC REAL_LE_TRANS THEN
  EXISTS_TAC `sum(1..dimindex(:N)) (\i. abs((x:real^N)$i))` THEN
  REWRITE_TAC[NORM_LE_L1] THEN MATCH_MP_TAC SUM_LE THEN
  ASM_SIMP_TAC[FINITE_NUMSEG; IN_NUMSEG; REAL_ARITH
   `a <= x /\ x <= b ==> abs(x) <= abs(a) + abs(b)`]);;


let BOUNDED_INTERVAL = 
prove
 (`(!a b. bounded (interval [a,b])) /\ (!a b. bounded (interval (a,b)))`,


let NOT_INTERVAL_UNIV = 
prove
 (`(!a b. ~(interval[a,b] = UNIV)) /\
   (!a b. ~(interval(a,b) = UNIV))`,


let COMPACT_INTERVAL = 
prove
 (`!a b. compact (interval [a,b])`,


let OPEN_INTERVAL_MIDPOINT = 
prove
 (`!a b:real^N.
        ~(interval(a,b) = {}) ==> (inv(&2) % (a + b)) IN interval(a,b)`,

  REWRITE_TAC[INTERVAL_NE_EMPTY; IN_INTERVAL] THEN
  SIMP_TAC[VECTOR_MUL_COMPONENT; VECTOR_ADD_COMPONENT] THEN
  REPEAT GEN_TAC THEN MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN REAL_ARITH_TAC);;


let OPEN_CLOSED_INTERVAL_CONVEX = 
prove
 (`!a b x y:real^N e.
        x IN interval(a,b) /\ y IN interval[a,b] /\ &0 < e /\ e <= &1
        ==> (e % x + (&1 - e) % y) IN interval(a,b)`,

  REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT
   `(c /\ d ==> a /\ b ==> e) ==> a /\ b /\ c /\ d ==> e`) THEN
  STRIP_TAC THEN REWRITE_TAC[IN_INTERVAL; AND_FORALL_THM] THEN
  SIMP_TAC[VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT] THEN
  MATCH_MP_TAC MONO_FORALL THEN
  GEN_TAC THEN DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
  ASM_REWRITE_TAC[] THEN STRIP_TAC THEN
  SUBST1_TAC(REAL_ARITH `(a:real^N)$i = e * a$i + (&1 - e) * a$i`) THEN
  SUBST1_TAC(REAL_ARITH `(b:real^N)$i = e * b$i + (&1 - e) * b$i`) THEN
  CONJ_TAC THEN MATCH_MP_TAC REAL_LTE_ADD2 THEN
  ASM_SIMP_TAC[REAL_LT_LMUL_EQ; REAL_LE_LMUL; REAL_SUB_LE]);;


let CLOSURE_OPEN_INTERVAL = 
prove
 (`!a b:real^N.
     ~(interval(a,b) = {}) ==> closure(interval(a,b)) = interval[a,b]`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
   [MATCH_MP_TAC CLOSURE_MINIMAL THEN
    REWRITE_TAC[INTERVAL_OPEN_SUBSET_CLOSED; CLOSED_INTERVAL];
    ALL_TAC] THEN
  REWRITE_TAC[SUBSET; closure; IN_UNION] THEN X_GEN_TAC `x:real^N` THEN
  DISCH_TAC THEN MATCH_MP_TAC(TAUT `(~b ==> c) ==> b \/ c`) THEN DISCH_TAC THEN
  REWRITE_TAC[IN_ELIM_THM; LIMPT_SEQUENTIAL] THEN
  ABBREV_TAC `(c:real^N) = inv(&2) % (a + b)` THEN
  EXISTS_TAC `\n. (x:real^N) + inv(&n + &1) % (c - x)` THEN CONJ_TAC THENL
   [X_GEN_TAC `n:num` THEN REWRITE_TAC[IN_DELETE] THEN
    REWRITE_TAC[VECTOR_ARITH `x + a = x <=> a = vec 0`] THEN
    REWRITE_TAC[VECTOR_MUL_EQ_0; REAL_INV_EQ_0] THEN
    REWRITE_TAC[VECTOR_SUB_EQ; REAL_ARITH `~(&n + &1 = &0)`] THEN
    CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[OPEN_INTERVAL_MIDPOINT]] THEN
    REWRITE_TAC[VECTOR_ARITH `x + a % (y - x) = a % y + (&1 - a) % x`] THEN
    MATCH_MP_TAC OPEN_CLOSED_INTERVAL_CONVEX THEN
    CONJ_TAC THENL [ASM_MESON_TAC[OPEN_INTERVAL_MIDPOINT]; ALL_TAC] THEN
    ASM_REWRITE_TAC[REAL_LT_INV_EQ; REAL_ARITH `&0 < &n + &1`] THEN
    MATCH_MP_TAC REAL_INV_LE_1 THEN REAL_ARITH_TAC;
    ALL_TAC] THEN
  GEN_REWRITE_TAC LAND_CONV [VECTOR_ARITH `x:real^N = x + &0 % (c - x)`] THEN
  MATCH_MP_TAC LIM_ADD THEN REWRITE_TAC[LIM_CONST] THEN
  MATCH_MP_TAC LIM_VMUL THEN REWRITE_TAC[LIM_CONST] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY; o_THM; DIST_LIFT; REAL_SUB_RZERO] THEN
  X_GEN_TAC `e:real` THEN GEN_REWRITE_TAC LAND_CONV [REAL_ARCH_INV] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  STRIP_TAC THEN X_GEN_TAC `n:num` THEN DISCH_TAC THEN
  REWRITE_TAC[REAL_ABS_INV] THEN MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `inv(&N)` THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC REAL_LE_INV2 THEN UNDISCH_TAC `N:num <= n` THEN
  UNDISCH_TAC `~(N = 0)` THEN
  REWRITE_TAC[GSYM LT_NZ; GSYM REAL_OF_NUM_LE; GSYM REAL_OF_NUM_LT] THEN
  REAL_ARITH_TAC);;


let CLOSURE_INTERVAL = 
prove
 (`(!a b. closure(interval[a,b]) = interval[a,b]) /\
   (!a b. closure(interval(a,b)) =
          if interval(a,b) = {} then {} else interval[a,b])`,

  SIMP_TAC[CLOSURE_CLOSED; CLOSED_INTERVAL] THEN REPEAT GEN_TAC THEN
  COND_CASES_TAC THEN ASM_SIMP_TAC[CLOSURE_OPEN_INTERVAL; CLOSURE_EMPTY]);;


let BOUNDED_SUBSET_OPEN_INTERVAL_SYMMETRIC = 
prove
 (`!s:real^N->bool. bounded s ==> ?a. s SUBSET interval(--a,a)`,

  REWRITE_TAC[BOUNDED_POS; LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`s:real^N->bool`; `B:real`] THEN STRIP_TAC THEN
  EXISTS_TAC `(lambda i. B + &1):real^N` THEN
  REWRITE_TAC[SUBSET] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  SIMP_TAC[IN_INTERVAL; LAMBDA_BETA; REAL_BOUNDS_LT; VECTOR_NEG_COMPONENT] THEN
  ASM_MESON_TAC[COMPONENT_LE_NORM;
                REAL_ARITH `x <= y ==> a <= x ==> a < y + &1`]);;


let BOUNDED_SUBSET_OPEN_INTERVAL = 
prove
 (`!s:real^N->bool. bounded s ==> ?a b. s SUBSET interval(a,b)`,


let BOUNDED_SUBSET_CLOSED_INTERVAL_SYMMETRIC = 
prove
 (`!s:real^N->bool. bounded s ==> ?a. s SUBSET interval[--a,a]`,

  GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP BOUNDED_SUBSET_OPEN_INTERVAL_SYMMETRIC) THEN
  MATCH_MP_TAC MONO_EXISTS THEN
  SIMP_TAC[IN_BALL; IN_INTERVAL; SUBSET; REAL_LT_IMP_LE]);;


let BOUNDED_SUBSET_CLOSED_INTERVAL = 
prove
 (`!s:real^N->bool. bounded s ==> ?a b. s SUBSET interval[a,b]`,


let FRONTIER_CLOSED_INTERVAL = 
prove
 (`!a b. frontier(interval[a,b]) = interval[a,b] DIFF interval(a,b)`,


let FRONTIER_OPEN_INTERVAL = 
prove
 (`!a b. frontier(interval(a,b)) =
                if interval(a,b) = {} then {}
                else interval[a,b] DIFF interval(a,b)`,

  REPEAT GEN_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[FRONTIER_EMPTY] THEN
  ASM_SIMP_TAC[frontier; CLOSURE_OPEN_INTERVAL; INTERIOR_OPEN;
               OPEN_INTERVAL]);;


let INTER_INTERVAL_MIXED_EQ_EMPTY = 
prove
 (`!a b c d:real^N.
        ~(interval(c,d) = {})
        ==> (interval(a,b) INTER interval[c,d] = {} <=>
             interval(a,b) INTER interval(c,d) = {})`,


let INTERVAL_TRANSLATION = 
prove
 (`(!c a b. interval[c + a,c + b] = IMAGE (\x. c + x) (interval[a,b])) /\
   (!c a b. interval(c + a,c + b) = IMAGE (\x. c + x) (interval(a,b)))`,

  REWRITE_TAC[interval] THEN CONJ_TAC THEN GEOM_TRANSLATE_TAC[] THEN
  REWRITE_TAC[VECTOR_ADD_COMPONENT; REAL_LT_LADD; REAL_LE_LADD]);;

add_translation_invariants
 [CONJUNCT1 INTERVAL_TRANSLATION; CONJUNCT2 INTERVAL_TRANSLATION];;


let EMPTY_AS_INTERVAL = 
prove
 (`{} = interval[vec 1,vec 0]`,

  SIMP_TAC[EXTENSION; NOT_IN_EMPTY; IN_INTERVAL; VEC_COMPONENT] THEN
  GEN_TAC THEN DISCH_THEN(MP_TAC o SPEC `1`) THEN
  REWRITE_TAC[LE_REFL; DIMINDEX_GE_1] THEN REAL_ARITH_TAC);;


let UNIT_INTERVAL_NONEMPTY = 
prove
 (`~(interval[vec 0:real^N,vec 1] = {}) /\
   ~(interval(vec 0:real^N,vec 1) = {})`,


let IMAGE_STRETCH_INTERVAL = 
prove
 (`!a b:real^N m.
    IMAGE (\x. lambda k. m(k) * x$k) (interval[a,b]) =
        if interval[a,b] = {} then {}
        else interval[(lambda k. min (m(k) * a$k) (m(k) * b$k)):real^N,
                      (lambda k. max (m(k) * a$k) (m(k) * b$k))]`,

  REPEAT GEN_TAC THEN COND_CASES_TAC THEN ASM_SIMP_TAC[IMAGE_CLAUSES] THEN
  ASM_SIMP_TAC[EXTENSION; IN_IMAGE; CART_EQ; IN_INTERVAL; AND_FORALL_THM;
               TAUT `(a ==> b) /\ (a ==> c) <=> a ==> b /\ c`;
                LAMBDA_BETA; GSYM LAMBDA_SKOLEM] THEN
  X_GEN_TAC `x:real^N` THEN MATCH_MP_TAC(MESON[]
   `(!x. p x ==> (q x <=> r x))
    ==> ((!x. p x ==> q x) <=> (!x. p x ==> r x))`) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INTERVAL_NE_EMPTY]) THEN
  MATCH_MP_TAC MONO_FORALL THEN
  X_GEN_TAC `k:num` THEN ASM_CASES_TAC `1 <= k /\ k <= dimindex(:N)` THEN
  ASM_REWRITE_TAC[] THEN ASM_CASES_TAC `(m:num->real) k = &0` THENL
   [ASM_REWRITE_TAC[REAL_MUL_LZERO; REAL_MAX_ACI; REAL_MIN_ACI] THEN
    ASM_MESON_TAC[REAL_LE_ANTISYM; REAL_LE_REFL];
    ALL_TAC] THEN
  ASM_SIMP_TAC[REAL_FIELD `~(m = &0) ==> (x = m * y <=> y = x / m)`] THEN
  REWRITE_TAC[UNWIND_THM2] THEN FIRST_X_ASSUM(DISJ_CASES_TAC o MATCH_MP
   (REAL_ARITH `~(z = &0) ==> &0 < z \/ &0 < --z`))
  THENL
   [ALL_TAC;
    ONCE_REWRITE_TAC[GSYM REAL_LE_NEG2] THEN
    ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
    REWRITE_TAC[REAL_ARITH `--(max a b) = min (--a) (--b)`;
                REAL_ARITH `--(min a b) = max (--a) (--b)`; real_div;
                GSYM REAL_MUL_RNEG; GSYM REAL_INV_NEG] THEN
    REWRITE_TAC[GSYM real_div]] THEN
  ASM_SIMP_TAC[REAL_LE_LDIV_EQ; REAL_LE_RDIV_EQ] THEN
  ASM_SIMP_TAC[real_min; real_max; REAL_LE_LMUL_EQ; REAL_LE_RMUL_EQ] THEN
  REAL_ARITH_TAC);;


let INTERVAL_IMAGE_STRETCH_INTERVAL = 
prove
 (`!a b:real^N m. ?u v:real^N.
     IMAGE (\x. lambda k. m k * x$k) (interval[a,b]) = interval[u,v]`,

  REWRITE_TAC[IMAGE_STRETCH_INTERVAL] THEN MESON_TAC[EMPTY_AS_INTERVAL]);;


let CLOSED_INTERVAL_IMAGE_UNIT_INTERVAL = 
prove
 (`!a b:real^N.
        ~(interval[a,b] = {})
        ==> interval[a,b] = IMAGE (\x:real^N. a + x)
                                  (IMAGE (\x. (lambda i. (b$i - a$i) * x$i))
                                         (interval[vec 0:real^N,vec 1]))`,

  REWRITE_TAC[INTERVAL_NE_EMPTY] THEN REPEAT STRIP_TAC THEN
  REWRITE_TAC[IMAGE_STRETCH_INTERVAL; UNIT_INTERVAL_NONEMPTY] THEN
  REWRITE_TAC[GSYM INTERVAL_TRANSLATION] THEN
  REWRITE_TAC[EXTENSION; IN_INTERVAL] THEN
  SIMP_TAC[LAMBDA_BETA; VECTOR_ADD_COMPONENT; VEC_COMPONENT] THEN
  GEN_TAC THEN REWRITE_TAC[REAL_MUL_RZERO; REAL_MUL_RID] THEN
  MATCH_MP_TAC(MESON[] `(!x. P x <=> Q x) ==> ((!x. P x) <=> (!x. Q x))`) THEN
  POP_ASSUM MP_TAC THEN MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `i:num` THEN
  ASM_CASES_TAC `1 <= i /\ i <= dimindex(:N)` THEN ASM_REWRITE_TAC[] THEN
  REAL_ARITH_TAC);;


let SUMS_INTERVALS = 
prove
 (`(!a b c d:real^N.
        ~(interval[a,b] = {}) /\ ~(interval[c,d] = {})
        ==> {x + y | x IN interval[a,b] /\ y IN interval[c,d]} =
            interval[a+c,b+d]) /\
   (!a b c d:real^N.
        ~(interval(a,b) = {}) /\ ~(interval(c,d) = {})
        ==> {x + y | x IN interval(a,b) /\ y IN interval(c,d)} =
            interval(a+c,b+d))`,

  CONJ_TAC THEN REPEAT GEN_TAC THEN REWRITE_TAC[INTERVAL_NE_EMPTY] THEN
  STRIP_TAC THEN REWRITE_TAC[EXTENSION; IN_INTERVAL; IN_ELIM_THM] THEN
  REWRITE_TAC[TAUT `(a /\ b) /\ c <=> c /\ a /\ b`] THEN
  REWRITE_TAC[VECTOR_ARITH `x:real^N = y + z <=> z = x - y`] THEN
  REWRITE_TAC[UNWIND_THM2; VECTOR_ADD_COMPONENT; VECTOR_SUB_COMPONENT] THEN
  (X_GEN_TAC `x:real^N` THEN EQ_TAC THENL
   [DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC);
    DISCH_TAC THEN
    REWRITE_TAC[AND_FORALL_THM; GSYM LAMBDA_SKOLEM;
                TAUT `(p ==> q) /\ (p ==> r) <=> p ==> q /\ r`] THEN
    REWRITE_TAC[REAL_ARITH
     `((a <= y /\ y <= b) /\ c <= x - y /\ x - y <= d <=>
       max a (x - d) <= y /\ y <= min b (x - c)) /\
      ((a < y /\ y < b) /\ c < x - y /\ x - y < d <=>
       max a (x - d) < y /\ y < min b (x - c))`] THEN
    REWRITE_TAC[GSYM REAL_LE_BETWEEN; GSYM REAL_LT_BETWEEN]] THEN
  X_GEN_TAC `i:num` THEN STRIP_TAC THEN
  REPEAT(FIRST_X_ASSUM(MP_TAC o SPEC `i:num`)) THEN
  ASM_REWRITE_TAC[] THEN ASM_REAL_ARITH_TAC));;


let PCROSS_INTERVAL = 
prove
 (`!a b:real^M c d:real^N.
        interval[a,b] PCROSS interval[c,d] =
        interval[pastecart a c,pastecart b d]`,

  REPEAT GEN_TAC THEN REWRITE_TAC[PCROSS] THEN
  REWRITE_TAC[EXTENSION; FORALL_PASTECART; IN_ELIM_PASTECART_THM] THEN
  SIMP_TAC[IN_INTERVAL; pastecart; LAMBDA_BETA; DIMINDEX_FINITE_SUM] THEN
  MAP_EVERY X_GEN_TAC [`x:real^M`; `y:real^N`] THEN EQ_TAC THEN STRIP_TAC THENL
   [X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    COND_CASES_TAC THEN ASM_SIMP_TAC[] THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_ARITH_TAC;
    CONJ_TAC THEN X_GEN_TAC `i:num` THEN STRIP_TAC THENL
     [FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN ASM_REWRITE_TAC[] THEN
      DISCH_THEN MATCH_MP_TAC THEN ASM_ARITH_TAC;
      FIRST_X_ASSUM(MP_TAC o SPEC `i + dimindex(:M)`) THEN
      COND_CASES_TAC THEN ASM_REWRITE_TAC[ADD_SUB] THENL
       [ASM_ARITH_TAC;
        DISCH_THEN MATCH_MP_TAC THEN ASM_ARITH_TAC]]]);;

let OPEN_CONTAINS_INTERVAL,OPEN_CONTAINS_OPEN_INTERVAL = (CONJ_PAIR o prove)
 (`(!s:real^N->bool.
        open s <=>
        !x. x IN s ==> ?a b. x IN interval(a,b) /\ interval[a,b] SUBSET s) /\
   (!s:real^N->bool.
        open s <=>
        !x. x IN s ==> ?a b. x IN interval(a,b) /\ interval(a,b) SUBSET s)`,
  REWRITE_TAC[AND_FORALL_THM] THEN GEN_TAC THEN
  MATCH_MP_TAC(TAUT
   `(q ==> r) /\ (r ==> p) /\ (p ==> q) ==> (p <=> q) /\ (p <=> r)`) THEN
  REPEAT CONJ_TAC THENL
   [MESON_TAC[SUBSET_TRANS; INTERVAL_OPEN_SUBSET_CLOSED];
    DISCH_TAC THEN REWRITE_TAC[OPEN_CONTAINS_BALL] THEN
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN
    ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`] THEN STRIP_TAC THEN
    MP_TAC(ISPEC `interval(a:real^N,b)` OPEN_CONTAINS_BALL) THEN
    REWRITE_TAC[OPEN_INTERVAL] THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC MONO_EXISTS THEN
    REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_MESON_TAC[SUBSET_TRANS; INTERVAL_OPEN_SUBSET_CLOSED];
    DISCH_TAC THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_ASSUM(MP_TAC o SPEC `x:real^N` o
      GEN_REWRITE_RULE I [OPEN_CONTAINS_CBALL]) THEN
    ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `x - e / &(dimindex(:N)) % vec 1:real^N` THEN
    EXISTS_TAC `x + e / &(dimindex(:N)) % vec 1:real^N` THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (SET_RULE
     `b SUBSET s ==> x IN i /\ j SUBSET b ==> x IN i /\ j SUBSET s`)) THEN
    SIMP_TAC[IN_INTERVAL; VECTOR_SUB_COMPONENT; VECTOR_MUL_COMPONENT; IN_CBALL;
             VEC_COMPONENT; VECTOR_ADD_COMPONENT; SUBSET; REAL_MUL_RID] THEN
    REWRITE_TAC[REAL_ARITH `x - e < x /\ x < x + e <=> &0 < e`;
                REAL_ARITH `x - e <= y /\ y <= x + e <=> abs(x - y) <= e`] THEN
    ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; LE_1; DIMINDEX_GE_1] THEN
    X_GEN_TAC `y:real^N` THEN REWRITE_TAC[GSYM VECTOR_SUB_COMPONENT] THEN
    DISCH_TAC THEN REWRITE_TAC[dist] THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN
    EXISTS_TAC `sum(1..dimindex(:N)) (\i. abs((x - y:real^N)$i))` THEN
    REWRITE_TAC[NORM_LE_L1] THEN MATCH_MP_TAC SUM_BOUND_GEN THEN
    ASM_SIMP_TAC[CARD_NUMSEG_1; IN_NUMSEG; FINITE_NUMSEG] THEN
    REWRITE_TAC[NUMSEG_EMPTY; NOT_LT; DIMINDEX_GE_1]]);;


let DIAMETER_INTERVAL = 
prove
 (`(!a b:real^N.
        diameter(interval[a,b]) =
        if interval[a,b] = {} then &0 else norm(b - a)) /\
   (!a b:real^N.
        diameter(interval(a,b)) =
        if interval(a,b) = {} then &0 else norm(b - a))`,

  REWRITE_TAC[AND_FORALL_THM] THEN REPEAT GEN_TAC THEN
  ASM_CASES_TAC `interval[a:real^N,b] = {}` THENL
   [ASM_MESON_TAC[INTERVAL_OPEN_SUBSET_CLOSED; SUBSET_EMPTY; DIAMETER_EMPTY];
    ASM_REWRITE_TAC[]] THEN
  MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
   [REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN
    ASM_SIMP_TAC[DIAMETER_BOUNDED_BOUND;
                 ENDS_IN_INTERVAL; BOUNDED_INTERVAL] THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC
     `diameter(cball(inv(&2) % (a + b):real^N,norm(b - a) / &2))` THEN
    CONJ_TAC THENL
     [MATCH_MP_TAC DIAMETER_SUBSET THEN REWRITE_TAC[BOUNDED_CBALL] THEN
      REWRITE_TAC[SUBSET; IN_INTERVAL; IN_CBALL] THEN
      GEN_TAC THEN DISCH_TAC THEN REWRITE_TAC[dist] THEN
      REWRITE_TAC[GSYM NORM_MUL; REAL_ARITH `x / &2 = abs(inv(&2)) * x`] THEN
      MATCH_MP_TAC NORM_LE_COMPONENTWISE THEN
      X_GEN_TAC `i:num` THEN DISCH_TAC THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN
      ASM_REWRITE_TAC[VECTOR_ADD_COMPONENT; VECTOR_SUB_COMPONENT;
                      VECTOR_MUL_COMPONENT] THEN
      REAL_ARITH_TAC;
      REWRITE_TAC[DIAMETER_CBALL] THEN NORM_ARITH_TAC];
    DISCH_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[DIAMETER_EMPTY] THEN
    SUBGOAL_THEN `interval[a:real^N,b] = closure(interval(a,b))`
    SUBST_ALL_TAC THEN ASM_REWRITE_TAC[CLOSURE_INTERVAL] THEN
    ASM_MESON_TAC[DIAMETER_CLOSURE; BOUNDED_INTERVAL]]);;


let IMAGE_TWIZZLE_INTERVAL = 
prove
 (`!p a b. dimindex(:M) = dimindex(:N) /\ p permutes 1..dimindex(:N)
           ==> IMAGE ((\x. lambda i. x$(p i)):real^M->real^N) (interval[a,b]) =
               interval[(lambda i. a$(p i)),(lambda i. b$(p i))]`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
  SIMP_TAC[IN_INTERVAL; CART_EQ; LAMBDA_BETA] THEN CONJ_TAC THENL
   [X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
    EXISTS_TAC `(lambda i. (y:real^N)$(inverse p i)):real^M` THEN
    IMP_REWRITE_TAC[LAMBDA_BETA] THEN
    ASM_REWRITE_TAC[GSYM IN_NUMSEG] THEN
    ASM_MESON_TAC[PERMUTES_INVERSE_EQ; PERMUTES_IN_IMAGE];
    REWRITE_TAC[GSYM IN_NUMSEG] THEN
    ASM_MESON_TAC[PERMUTES_INVERSES; PERMUTES_IN_IMAGE]]);;

(* ------------------------------------------------------------------------- *)
(* Some special cases for intervals in R^1.                                  *)
(* ------------------------------------------------------------------------- *)


let INTERVAL_CASES_1 = 
prove
 (`!x:real^1. x IN interval[a,b] ==> x IN interval(a,b) \/ (x = a) \/ (x = b)`,

  REWRITE_TAC[CART_EQ; IN_INTERVAL; FORALL_DIMINDEX_1] THEN REAL_ARITH_TAC);;


let IN_INTERVAL_1 = 
prove
 (`!a b x:real^1.
        (x IN interval[a,b] <=> drop a <= drop x /\ drop x <= drop b) /\
        (x IN interval(a,b) <=> drop a < drop x /\ drop x < drop b)`,

  REWRITE_TAC[IN_INTERVAL; drop; CONJ_ASSOC; DIMINDEX_1; LE_ANTISYM] THEN
  MESON_TAC[]);;


let INTERVAL_EQ_EMPTY_1 = 
prove
 (`!a b:real^1.
        (interval[a,b] = {} <=> drop b < drop a) /\
        (interval(a,b) = {} <=> drop b <= drop a)`,

  REWRITE_TAC[INTERVAL_EQ_EMPTY; drop; CONJ_ASSOC; DIMINDEX_1; LE_ANTISYM] THEN
  MESON_TAC[]);;


let INTERVAL_NE_EMPTY_1 = 
prove
 (`(!a b:real^1. ~(interval[a,b] = {}) <=> drop a <= drop b) /\
   (!a b:real^1. ~(interval(a,b) = {}) <=> drop a < drop b)`,

  REWRITE_TAC[INTERVAL_EQ_EMPTY_1] THEN REAL_ARITH_TAC);;


let SUBSET_INTERVAL_1 = 
prove
 (`!a b c d.
        (interval[a,b] SUBSET interval[c,d] <=>
                drop b < drop a \/
                drop c <= drop a /\ drop a <= drop b /\ drop b <= drop d) /\
        (interval[a,b] SUBSET interval(c,d) <=>
                drop b < drop a \/
                drop c < drop a /\ drop a <= drop b /\ drop b < drop d) /\
        (interval(a,b) SUBSET interval[c,d] <=>
                drop b <= drop a \/
                drop c <= drop a /\ drop a < drop b /\ drop b <= drop d) /\
        (interval(a,b) SUBSET interval(c,d) <=>
                drop b <= drop a \/
                drop c <= drop a /\ drop a < drop b /\ drop b <= drop d)`,

  REWRITE_TAC[SUBSET_INTERVAL; FORALL_1; DIMINDEX_1; drop] THEN
  REAL_ARITH_TAC);;


let EQ_INTERVAL_1 = 
prove
 (`!a b c d:real^1.
       (interval[a,b] = interval[c,d] <=>
          drop b < drop a /\ drop d < drop c \/
          drop a = drop c /\ drop b = drop d)`,

  REWRITE_TAC[SET_RULE `s = t <=> s SUBSET t /\ t SUBSET s`] THEN
  REWRITE_TAC[SUBSET_INTERVAL_1] THEN REAL_ARITH_TAC);;


let DISJOINT_INTERVAL_1 = 
prove
 (`!a b c d:real^1.
        (interval[a,b] INTER interval[c,d] = {} <=>
          drop b < drop a \/ drop d < drop c \/
          drop b < drop c \/ drop d < drop a) /\
        (interval[a,b] INTER interval(c,d) = {} <=>
          drop b < drop a \/ drop d <= drop c \/
          drop b <= drop c \/ drop d <= drop a) /\
        (interval(a,b) INTER interval[c,d] = {} <=>
          drop b <= drop a \/ drop d < drop c \/
          drop b <= drop c \/ drop d <= drop a) /\
        (interval(a,b) INTER interval(c,d) = {} <=>
          drop b <= drop a \/ drop d <= drop c \/
          drop b <= drop c \/ drop d <= drop a)`,

  REWRITE_TAC[DISJOINT_INTERVAL; CONJ_ASSOC; DIMINDEX_1; LE_ANTISYM;
              UNWIND_THM1; drop]);;


let OPEN_CLOSED_INTERVAL_1 = 
prove
 (`!a b:real^1. interval(a,b) = interval[a,b] DIFF {a,b}`,

  REWRITE_TAC[EXTENSION; IN_INTERVAL_1; IN_DIFF; IN_INSERT; NOT_IN_EMPTY] THEN
  REWRITE_TAC[GSYM DROP_EQ] THEN REAL_ARITH_TAC);;


let CLOSED_OPEN_INTERVAL_1 = 
prove
 (`!a b:real^1. drop a <= drop b ==> interval[a,b] = interval(a,b) UNION {a,b}`,

  REWRITE_TAC[EXTENSION; IN_INTERVAL_1; IN_UNION; IN_INSERT; NOT_IN_EMPTY] THEN
  REWRITE_TAC[GSYM DROP_EQ] THEN REAL_ARITH_TAC);;


let BALL_1 = 
prove
 (`!x:real^1 r. cball(x,r) = interval[x - lift r,x + lift r] /\
                ball(x,r) = interval(x - lift r,x + lift r)`,

  REWRITE_TAC[EXTENSION; IN_BALL; IN_CBALL; IN_INTERVAL_1] THEN
  REWRITE_TAC[dist; NORM_REAL; GSYM drop; DROP_SUB; LIFT_DROP; DROP_ADD] THEN
  REAL_ARITH_TAC);;


let SPHERE_1 = 
prove
 (`!a:real^1 r. sphere(a,r) = if r < &0 then {} else {a - lift r,a + lift r}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sphere] THEN COND_CASES_TAC THEN
  REWRITE_TAC[DIST_REAL; GSYM drop; FORALL_DROP] THEN
  REWRITE_TAC[EXTENSION; IN_INSERT; NOT_IN_EMPTY; IN_ELIM_THM] THEN
  REWRITE_TAC[GSYM DROP_EQ; DROP_ADD; DROP_SUB; LIFT_DROP] THEN
  ASM_REAL_ARITH_TAC);;


let FINITE_SPHERE_1 = 
prove
 (`!a:real^1 r. FINITE(sphere(a,r))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[SPHERE_1] THEN
  MESON_TAC[FINITE_INSERT; FINITE_EMPTY]);;


let FINITE_INTERVAL_1 = 
prove
 (`(!a b. FINITE(interval[a,b]) <=> drop b <= drop a) /\
   (!a b. FINITE(interval(a,b)) <=> drop b <= drop a)`,

  REWRITE_TAC[OPEN_CLOSED_INTERVAL_1] THEN
  REWRITE_TAC[SET_RULE `s DIFF {a,b} = s DELETE a DELETE b`] THEN
  REWRITE_TAC[FINITE_DELETE] THEN REPEAT GEN_TAC THEN
  SUBGOAL_THEN `interval[a,b] = IMAGE lift {x | drop a <= x /\ x <= drop b}`
  SUBST1_TAC THENL
   [CONV_TAC SYM_CONV THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
    CONJ_TAC THENL [MESON_TAC[LIFT_DROP]; ALL_TAC] THEN
    REWRITE_TAC[IN_INTERVAL_1; IN_ELIM_THM; LIFT_DROP];
    SIMP_TAC[FINITE_IMAGE_INJ_EQ; LIFT_EQ; FINITE_REAL_INTERVAL]]);;


let BALL_INTERVAL = 
prove
 (`!x:real^1 e. ball(x,e) = interval(x - lift e,x + lift e)`,

  REWRITE_TAC[EXTENSION; IN_BALL; IN_INTERVAL_1; DIST_REAL] THEN
  REWRITE_TAC[GSYM drop; DROP_SUB; DROP_ADD; LIFT_DROP] THEN REAL_ARITH_TAC);;


let CBALL_INTERVAL = 
prove
 (`!x:real^1 e. cball(x,e) = interval[x - lift e,x + lift e]`,

  REWRITE_TAC[EXTENSION; IN_CBALL; IN_INTERVAL_1; DIST_REAL] THEN
  REWRITE_TAC[GSYM drop; DROP_SUB; DROP_ADD; LIFT_DROP] THEN REAL_ARITH_TAC);;


let BALL_INTERVAL_0 = 
prove
 (`!e. ball(vec 0:real^1,e) = interval(--lift e,lift e)`,

  GEN_TAC THEN REWRITE_TAC[BALL_INTERVAL] THEN AP_TERM_TAC THEN
  BINOP_TAC THEN VECTOR_ARITH_TAC);;


let CBALL_INTERVAL_0 = 
prove
 (`!e. cball(vec 0:real^1,e) = interval[--lift e,lift e]`,

  GEN_TAC THEN REWRITE_TAC[CBALL_INTERVAL] THEN AP_TERM_TAC THEN
  AP_THM_TAC THEN AP_TERM_TAC THEN BINOP_TAC THEN VECTOR_ARITH_TAC);;


let INTER_INTERVAL_1 = 
prove
 (`!a b c d:real^1.
        interval[a,b] INTER interval[c,d] =
        interval[lift(max (drop a) (drop c)),lift(min (drop b) (drop d))]`,

  REWRITE_TAC[EXTENSION; IN_INTER; IN_INTERVAL_1; real_max; real_min] THEN
  REPEAT GEN_TAC THEN
  REPEAT(COND_CASES_TAC THEN ASM_REWRITE_TAC[LIFT_DROP]) THEN
  ASM_REAL_ARITH_TAC);;


let CLOSED_DIFF_OPEN_INTERVAL_1 = 
prove
 (`!a b:real^1.
        interval[a,b] DIFF interval(a,b) =
        if interval[a,b] = {} then {} else {a,b}`,

  REWRITE_TAC[EXTENSION; IN_DIFF; INTERVAL_EQ_EMPTY_1; IN_INTERVAL_1] THEN
  REPEAT GEN_TAC THEN COND_CASES_TAC THEN
  ASM_REWRITE_TAC[NOT_IN_EMPTY; IN_INSERT; NOT_IN_EMPTY] THEN
  REWRITE_TAC[GSYM DROP_EQ] THEN ASM_REAL_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Intervals in general, including infinite and mixtures of open and closed. *)
(* ------------------------------------------------------------------------- *)


let is_interval = new_definition
  `is_interval(s:real^N->bool) <=>
        !a b x. a IN s /\ b IN s /\
                (!i. 1 <= i /\ i <= dimindex(:N)
                     ==> (a$i <= x$i /\ x$i <= b$i) \/
                         (b$i <= x$i /\ x$i <= a$i))
                ==> x IN s`;;


let IS_INTERVAL_INTERVAL = 
prove
 (`!a:real^N b. is_interval(interval (a,b)) /\ is_interval(interval [a,b])`,


let IS_INTERVAL_EMPTY = 
prove
 (`is_interval {}`,

  REWRITE_TAC[is_interval; NOT_IN_EMPTY]);;


let IS_INTERVAL_UNIV = 
prove
 (`is_interval(UNIV:real^N->bool)`,

  REWRITE_TAC[is_interval; IN_UNIV]);;


let IS_INTERVAL_TRANSLATION_EQ = 
prove
 (`!a:real^N s. is_interval(IMAGE (\x. a + x) s) <=> is_interval s`,

  REWRITE_TAC[is_interval] THEN GEOM_TRANSLATE_TAC[] THEN
  REWRITE_TAC[VECTOR_ADD_COMPONENT; REAL_LT_LADD; REAL_LE_LADD]);;

add_translation_invariants [IS_INTERVAL_TRANSLATION_EQ];;


let IS_INTERVAL_TRANSLATION = 
prove
 (`!s a:real^N. is_interval s ==> is_interval(IMAGE (\x. a + x) s)`,


let IS_INTERVAL_POINTWISE = 
prove
 (`!s:real^N->bool x.
        is_interval s /\
        (!i. 1 <= i /\ i <= dimindex(:N) ==> ?a. a IN s /\ a$i = x$i)
        ==> x IN s`,

  REWRITE_TAC[is_interval] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
    `!n. ?y:real^N. (!i. 1 <= i /\ i <= n ==> y$i = (x:real^N)$i) /\ y IN s`
  MP_TAC THENL
   [INDUCT_TAC THEN REWRITE_TAC[ARITH_RULE `~(1 <= i /\ i <= 0)`] THENL
     [ASM_MESON_TAC[DIMINDEX_GE_1; LE_REFL]; ALL_TAC] THEN
    FIRST_X_ASSUM(X_CHOOSE_TAC `y:real^N`) THEN
    ASM_CASES_TAC `SUC n <= dimindex(:N)` THENL
     [FIRST_X_ASSUM(MP_TAC o SPEC `SUC n`) THEN
      ANTS_TAC THENL [ASM_ARITH_TAC; ALL_TAC] THEN
      DISCH_THEN(X_CHOOSE_THEN `z:real^N` STRIP_ASSUME_TAC) THEN
      EXISTS_TAC
       `(lambda i. if i <= n then (y:real^N)$i else (z:real^N)$i):real^N` THEN
      CONJ_TAC THENL
       [X_GEN_TAC `i:num` THEN STRIP_TAC THEN
        SUBGOAL_THEN `i <= dimindex(:N)` ASSUME_TAC THENL
         [ASM_ARITH_TAC; ASM_SIMP_TAC[LAMBDA_BETA]] THEN
        COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
        SUBGOAL_THEN `i = SUC n` (fun th -> ASM_REWRITE_TAC[th]) THEN
        ASM_ARITH_TAC;
        FIRST_X_ASSUM(ASSUME_TAC o CONJUNCT2) THEN
        FIRST_X_ASSUM MATCH_MP_TAC THEN
        MAP_EVERY EXISTS_TAC [`y:real^N`; `z:real^N`] THEN
        ASM_SIMP_TAC[LAMBDA_BETA] THEN REAL_ARITH_TAC];
      EXISTS_TAC `y:real^N` THEN ASM_REWRITE_TAC[] THEN
      SUBGOAL_THEN `y:real^N = x` (fun th -> REWRITE_TAC[th]) THEN
      REWRITE_TAC[CART_EQ] THEN
      ASM_MESON_TAC[ARITH_RULE `i <= N /\ ~(SUC n <= N) ==> i <= n`]];
    DISCH_THEN(MP_TAC o SPEC `dimindex(:N)`) THEN
    REWRITE_TAC[GSYM CART_EQ] THEN MESON_TAC[]]);;


let IS_INTERVAL_COMPACT = 
prove
 (`!s:real^N->bool. is_interval s /\ compact s <=> ?a b. s = interval[a,b]`,

  GEN_TAC THEN EQ_TAC THEN STRIP_TAC THEN
  ASM_SIMP_TAC[IS_INTERVAL_INTERVAL; COMPACT_INTERVAL] THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [ASM_MESON_TAC[EMPTY_AS_INTERVAL]; ALL_TAC] THEN
  EXISTS_TAC `(lambda i. inf { (x:real^N)$i | x IN s}):real^N` THEN
  EXISTS_TAC `(lambda i. sup { (x:real^N)$i | x IN s}):real^N` THEN
  SIMP_TAC[EXTENSION; IN_INTERVAL; LAMBDA_BETA] THEN X_GEN_TAC `x:real^N` THEN
  EQ_TAC THENL
   [DISCH_TAC THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    MP_TAC(ISPEC `{ (x:real^N)$i | x IN s}` INF) THEN
    MP_TAC(ISPEC `{ (x:real^N)$i | x IN s}` SUP) THEN
    ONCE_REWRITE_TAC[SIMPLE_IMAGE] THEN
    ASM_REWRITE_TAC[IMAGE_EQ_EMPTY; FORALL_IN_IMAGE] THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP COMPACT_IMP_BOUNDED) THEN
    REWRITE_TAC[bounded] THEN
    ASM_MESON_TAC[COMPONENT_LE_NORM; REAL_LE_TRANS; MEMBER_NOT_EMPTY;
                  REAL_ARITH `abs(x) <= B ==> --B <= x /\ x <= B`];
    DISCH_TAC THEN MATCH_MP_TAC IS_INTERVAL_POINTWISE THEN
    ASM_REWRITE_TAC[] THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    SUBGOAL_THEN
     `?a b:real^N. a IN s /\ b IN s /\ a$i <= (x:real^N)$i /\ x$i <= b$i`
    STRIP_ASSUME_TAC THENL
     [MP_TAC(ISPECL [`\x:real^N. x$i`; `s:real^N->bool`]
        CONTINUOUS_ATTAINS_INF) THEN
      ASM_SIMP_TAC[CONTINUOUS_ON_LIFT_COMPONENT; o_DEF] THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN STRIP_TAC THEN
      MP_TAC(ISPECL [`\x:real^N. x$i`; `s:real^N->bool`]
        CONTINUOUS_ATTAINS_SUP) THEN
      ASM_SIMP_TAC[CONTINUOUS_ON_LIFT_COMPONENT; o_DEF] THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:real^N` THEN STRIP_TAC THEN
      ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC REAL_LE_TRANS THENL
       [EXISTS_TAC `inf {(x:real^N)$i | x IN s}` THEN ASM_SIMP_TAC[] THEN
        MATCH_MP_TAC REAL_LE_INF THEN ASM SET_TAC[];
        EXISTS_TAC `sup {(x:real^N)$i | x IN s}` THEN ASM_SIMP_TAC[] THEN
        MATCH_MP_TAC REAL_SUP_LE THEN ASM SET_TAC[]];
      EXISTS_TAC
       `(lambda j. if j = i then (x:real^N)$i else (a:real^N)$j):real^N` THEN
      ASM_SIMP_TAC[LAMBDA_BETA] THEN
      FIRST_ASSUM(MATCH_MP_TAC o REWRITE_RULE[is_interval]) THEN
      MAP_EVERY EXISTS_TAC
       [`a:real^N`;
        `(lambda j. if j = i then (b:real^N)$i else (a:real^N)$j):real^N`] THEN
      ASM_SIMP_TAC[LAMBDA_BETA] THEN CONJ_TAC THENL
       [FIRST_X_ASSUM(MATCH_MP_TAC o REWRITE_RULE[is_interval]) THEN
        MAP_EVERY EXISTS_TAC [`a:real^N`; `b:real^N`] THEN
        ASM_SIMP_TAC[LAMBDA_BETA];
        ALL_TAC] THEN
      GEN_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
      ASM_REAL_ARITH_TAC]]);;


let IS_INTERVAL_1 = 
prove
 (`!s:real^1->bool.
        is_interval s <=>
          !a b x. a IN s /\ b IN s /\ drop a <= drop x /\ drop x <= drop b
                  ==> x IN s`,

  REWRITE_TAC[is_interval; DIMINDEX_1; FORALL_1; GSYM drop] THEN
  REWRITE_TAC[FORALL_LIFT; LIFT_DROP] THEN MESON_TAC[]);;


let IS_INTERVAL_1_CASES = 
prove
 (`!s:real^1->bool.
        is_interval s <=>
        s = {} \/
        s = (:real^1) \/
        (?a. s = {x | a < drop x}) \/
        (?a. s = {x | a <= drop x}) \/
        (?b. s = {x | drop x <= b}) \/
        (?b. s = {x | drop x < b}) \/
        (?a b. s = {x | a < drop x /\ drop x < b}) \/
        (?a b. s = {x | a < drop x /\ drop x <= b}) \/
        (?a b. s = {x | a <= drop x /\ drop x < b}) \/
        (?a b. s = {x | a <= drop x /\ drop x <= b})`,

  GEN_TAC THEN REWRITE_TAC[IS_INTERVAL_1] THEN EQ_TAC THENL
   [DISCH_TAC;
    STRIP_TAC THEN ASM_REWRITE_TAC[IN_ELIM_THM; IN_UNIV; NOT_IN_EMPTY] THEN
    REAL_ARITH_TAC] THEN
  ASM_CASES_TAC `s:real^1->bool = {}` THEN ASM_REWRITE_TAC[] THEN
  MP_TAC(ISPEC `IMAGE drop s` SUP) THEN
  MP_TAC(ISPEC `IMAGE drop s` INF) THEN
  ASM_REWRITE_TAC[IMAGE_EQ_EMPTY; FORALL_IN_IMAGE] THEN
  ASM_CASES_TAC `?a. !x. x IN s ==> a <= drop x` THEN
  ASM_CASES_TAC `?b. !x. x IN s ==> drop x <= b` THEN
  ASM_REWRITE_TAC[] THENL
   [STRIP_TAC THEN STRIP_TAC THEN
    MAP_EVERY ASM_CASES_TAC
     [`inf(IMAGE drop s) IN IMAGE drop s`; `sup(IMAGE drop s) IN IMAGE drop s`]
    THENL
     [REPLICATE_TAC 8 DISJ2_TAC;
      REPLICATE_TAC 7 DISJ2_TAC THEN DISJ1_TAC;
      REPLICATE_TAC 6 DISJ2_TAC THEN DISJ1_TAC;
      REPLICATE_TAC 5 DISJ2_TAC THEN DISJ1_TAC] THEN
    MAP_EVERY EXISTS_TAC [`inf(IMAGE drop s)`; `sup(IMAGE drop s)`];
    STRIP_TAC THEN ASM_CASES_TAC `inf(IMAGE drop s) IN IMAGE drop s` THENL
     [REPLICATE_TAC 2 DISJ2_TAC THEN DISJ1_TAC;
      DISJ2_TAC THEN DISJ1_TAC] THEN
    EXISTS_TAC `inf(IMAGE drop s)`;
    STRIP_TAC THEN ASM_CASES_TAC `sup(IMAGE drop s) IN IMAGE drop s` THENL
     [REPLICATE_TAC 3 DISJ2_TAC THEN DISJ1_TAC;
      REPLICATE_TAC 4 DISJ2_TAC THEN DISJ1_TAC] THEN
    EXISTS_TAC `sup(IMAGE drop s)`;
    DISJ1_TAC] THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_UNIV] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[IN_IMAGE]) THEN
  REWRITE_TAC[GSYM REAL_NOT_LE] THEN
  ASM_MESON_TAC[REAL_LE_TRANS; REAL_LE_TOTAL; REAL_LE_ANTISYM]);;


let IS_INTERVAL_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool.
        is_interval s /\ is_interval t ==> is_interval(s PCROSS t)`,

  REWRITE_TAC[is_interval; DIMINDEX_FINITE_SUM] THEN
  REWRITE_TAC[FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
  REPEAT GEN_TAC THEN
  MATCH_MP_TAC(MESON[]
   `(!a b a' b' x x'. P a b x /\ Q a' b' x' ==> R a b x a' b' x')
    ==> (!a b x. P a b x) /\ (!a' b' x'. Q a' b' x')
        ==> (!a a' b b' x x'. R a b x a' b' x')`) THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_REWRITE_TAC[] THEN X_GEN_TAC `i:num` THEN STRIP_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN
    ASM_SIMP_TAC[pastecart; LAMBDA_BETA; DIMINDEX_FINITE_SUM;
                 ARITH_RULE `x:num <= m ==> x <= m + n`];
    FIRST_X_ASSUM(MP_TAC o SPEC `dimindex(:M) + i`) THEN
    ASM_SIMP_TAC[pastecart; LAMBDA_BETA; DIMINDEX_FINITE_SUM;
                 ARITH_RULE `x:num <= n ==> m + x <= m + n`;
                 ARITH_RULE `1 <= x ==> 1 <= m + x`] THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[ADD_SUB2] THEN ASM_ARITH_TAC]);;


let IS_INTERVAL_PCROSS_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool.
        is_interval(s PCROSS t) <=>
        s = {} \/ t = {} \/ is_interval s /\ is_interval t`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s:real^M->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; IS_INTERVAL_EMPTY] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[PCROSS_EMPTY; IS_INTERVAL_EMPTY] THEN
  EQ_TAC THEN REWRITE_TAC[IS_INTERVAL_PCROSS] THEN
  REWRITE_TAC[is_interval] THEN
  REWRITE_TAC[FORALL_PASTECART; PASTECART_IN_PCROSS] THEN
  STRIP_TAC THEN CONJ_TAC THENL
   [MAP_EVERY X_GEN_TAC [`a:real^M`; `b:real^M`; `x:real^M`] THEN
    STRIP_TAC THEN UNDISCH_TAC `~(t:real^N->bool = {})` THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
    DISCH_THEN(X_CHOOSE_TAC `y:real^N`) THEN
    FIRST_X_ASSUM(MP_TAC o SPECL
     [`a:real^M`; `y:real^N`; `b:real^M`;
      `y:real^N`; `x:real^M`; `y:real^N`]);
    MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`; `x:real^N`] THEN
    STRIP_TAC THEN UNDISCH_TAC `~(s:real^M->bool = {})` THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
    DISCH_THEN(X_CHOOSE_TAC `w:real^M`) THEN
    FIRST_X_ASSUM(MP_TAC o SPECL
     [`w:real^M`; `a:real^N`; `w:real^M`;
      `b:real^N`; `w:real^M`; `x:real^N`])] THEN
  ASM_REWRITE_TAC[] THEN DISCH_THEN MATCH_MP_TAC THEN
  SIMP_TAC[pastecart; LAMBDA_BETA] THEN
  REPEAT STRIP_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[REAL_LE_REFL] THEN
  ASM_MESON_TAC[DIMINDEX_FINITE_SUM; ARITH_RULE
      `1 <= i /\ i <= m + n /\ ~(i <= m) ==> 1 <= i - m /\ i - m <= n`]);;


let IS_INTERVAL_INTER = 
prove
 (`!s t:real^N->bool.
        is_interval s /\ is_interval t ==> is_interval(s INTER t)`,

  REWRITE_TAC[is_interval; IN_INTER] THEN REPEAT GEN_TAC THEN STRIP_TAC THEN
  MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`; `x:real^N`] THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  MAP_EVERY EXISTS_TAC [`a:real^N`; `b:real^N`] THEN ASM_REWRITE_TAC[]);;


let INTERVAL_SUBSET_IS_INTERVAL = 
prove
 (`!s a b:real^N.
     is_interval s
     ==> (interval[a,b] SUBSET s <=> interval[a,b] = {} \/ a IN s /\ b IN s)`,

  REWRITE_TAC[is_interval] THEN REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `interval[a:real^N,b] = {}` THEN
  ASM_REWRITE_TAC[EMPTY_SUBSET] THEN
  EQ_TAC THENL [ASM_MESON_TAC[ENDS_IN_INTERVAL; SUBSET]; ALL_TAC] THEN
  REWRITE_TAC[SUBSET; IN_INTERVAL] THEN ASM_MESON_TAC[]);;


let INTERVAL_CONTAINS_COMPACT_NEIGHBOURHOOD = 
prove
 (`!s x:real^N.
        is_interval s /\ x IN s
        ==> ?a b d. &0 < d /\ x IN interval[a,b] /\
                    interval[a,b] SUBSET s /\
                    ball(x,d) INTER s SUBSET interval[a,b]`,

  REPEAT STRIP_TAC THEN ASM_SIMP_TAC[INTERVAL_SUBSET_IS_INTERVAL] THEN
  SUBGOAL_THEN
   `!i. 1 <= i /\ i <= dimindex(:N)
        ==> ?a. (?y. y IN s /\ y$i = a) /\
                (a < x$i \/ a = (x:real^N)$i /\
                            !y:real^N. y IN s ==> a <= y$i)`
  MP_TAC THENL [ASM_MESON_TAC[REAL_NOT_LT]; REWRITE_TAC[LAMBDA_SKOLEM]] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN STRIP_TAC THEN
  SUBGOAL_THEN
   `!i. 1 <= i /\ i <= dimindex(:N)
        ==> ?b. (?y. y IN s /\ y$i = b) /\
                (x$i < b \/ b = (x:real^N)$i /\
                            !y:real^N. y IN s ==> y$i <= b)`
  MP_TAC THENL [ASM_MESON_TAC[REAL_NOT_LT]; REWRITE_TAC[LAMBDA_SKOLEM]] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:real^N` THEN STRIP_TAC THEN
  EXISTS_TAC `min (inf (IMAGE (\i. if a$i < x$i
                                   then (x:real^N)$i - (a:real^N)$i else &1)
                              (1..dimindex(:N))))
                  (inf (IMAGE (\i. if x$i < b$i
                                   then (b:real^N)$i - x$i else &1)
                              (1..dimindex(:N))))` THEN
  REWRITE_TAC[REAL_LT_MIN; SUBSET; IN_BALL; IN_INTER] THEN
  SIMP_TAC[REAL_LT_INF_FINITE; IMAGE_EQ_EMPTY; FINITE_IMAGE;
           FINITE_NUMSEG; NUMSEG_EMPTY; GSYM NOT_LE; DIMINDEX_GE_1] THEN
  REWRITE_TAC[FORALL_IN_IMAGE; IN_INTERVAL] THEN REPEAT CONJ_TAC THENL
   [MESON_TAC[REAL_SUB_LT; REAL_LT_01];
    MESON_TAC[REAL_SUB_LT; REAL_LT_01];
    ASM_MESON_TAC[REAL_LE_LT];
    DISJ2_TAC THEN CONJ_TAC THEN MATCH_MP_TAC IS_INTERVAL_POINTWISE THEN
    ASM_MESON_TAC[];
    X_GEN_TAC `y:real^N` THEN
    DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
    REWRITE_TAC[AND_FORALL_THM] THEN MATCH_MP_TAC MONO_FORALL THEN
    X_GEN_TAC `i:num` THEN DISCH_THEN(fun th -> STRIP_TAC THEN MP_TAC th) THEN
    ASM_REWRITE_TAC[IN_NUMSEG] THEN MATCH_MP_TAC MONO_AND THEN CONJ_TAC THEN
    (COND_CASES_TAC THENL [REWRITE_TAC[dist]; ASM_MESON_TAC[]]) THEN
    DISCH_TAC THEN MP_TAC(ISPECL [`x - y:real^N`; `i:num`]
      COMPONENT_LE_NORM) THEN
    ASM_REWRITE_TAC[VECTOR_SUB_COMPONENT] THEN ASM_REAL_ARITH_TAC]);;


let IS_INTERVAL_SUMS = 
prove
 (`!s t:real^N->bool.
        is_interval s /\ is_interval t
        ==> is_interval {x + y | x IN s /\ y IN t}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[is_interval] THEN
  REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN
  REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN
  REWRITE_TAC[IMP_IMP; GSYM CONJ_ASSOC] THEN
  MAP_EVERY X_GEN_TAC
   [`a:real^N`; `a':real^N`; `b:real^N`; `b':real^N`; `y:real^N`] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (MP_TAC o SPECL [`a:real^N`; `b:real^N`]) MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (MP_TAC o SPECL [`a':real^N`; `b':real^N`]) STRIP_ASSUME_TAC) THEN
  ASM_REWRITE_TAC[IMP_IMP; IN_ELIM_THM] THEN  ONCE_REWRITE_TAC[CONJ_SYM] THEN
  ONCE_REWRITE_TAC[VECTOR_ARITH `z:real^N = x + y <=> y = z - x`] THEN
  REWRITE_TAC[UNWIND_THM2] THEN MATCH_MP_TAC(MESON[]
   `(?x. P x /\ Q(f x))
    ==> (!x. P x ==> x IN s) /\ (!x. Q x ==> x IN t)
        ==> ?x. x IN s /\ f x IN t`) THEN
  REWRITE_TAC[VECTOR_SUB_COMPONENT; AND_FORALL_THM;
              TAUT `(p ==> q) /\ (p ==> r) <=> p ==> q /\ r`] THEN
  REWRITE_TAC[GSYM LAMBDA_SKOLEM] THEN
  X_GEN_TAC `i:num` THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN
  ASM_REWRITE_TAC[VECTOR_ADD_COMPONENT] THEN
  REWRITE_TAC[REAL_ARITH
   `c <= y - x /\ y - x <= d <=> y - d <= x /\ x <= y - c`] THEN
  REWRITE_TAC[REAL_ARITH
  `a <= x /\ x <= b \/ b <= x /\ x <= a <=> min a b <= x /\ x <= max a b`] THEN
  ONCE_REWRITE_TAC[TAUT `(p /\ q) /\ (r /\ s) <=> (p /\ r) /\ (q /\ s)`] THEN
  REWRITE_TAC[GSYM REAL_LE_MIN; GSYM REAL_MAX_LE] THEN
  REWRITE_TAC[GSYM REAL_LE_BETWEEN] THEN REAL_ARITH_TAC);;


let IS_INTERVAL_SING = 
prove
 (`!a:real^N. is_interval {a}`,

  SIMP_TAC[is_interval; IN_SING; IMP_CONJ; CART_EQ; REAL_LE_ANTISYM]);;


let IS_INTERVAL_SCALING = 
prove
 (`!s:real^N->bool c. is_interval s ==> is_interval(IMAGE (\x. c % x) s)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `c = &0` THENL
   [ASM_REWRITE_TAC[VECTOR_MUL_LZERO] THEN
    SUBGOAL_THEN `IMAGE ((\x. vec 0):real^N->real^N) s = {} \/
                  IMAGE ((\x. vec 0):real^N->real^N) s = {vec 0}`
    STRIP_ASSUME_TAC THENL
     [SET_TAC[];
      ASM_REWRITE_TAC[IS_INTERVAL_EMPTY];
      ASM_REWRITE_TAC[IS_INTERVAL_SING]];
    REWRITE_TAC[is_interval; IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN
    REWRITE_TAC[FORALL_IN_IMAGE] THEN
    GEN_REWRITE_TAC (BINOP_CONV o REDEPTH_CONV) [RIGHT_IMP_FORALL_THM] THEN
    REWRITE_TAC[IMP_IMP; VECTOR_MUL_COMPONENT] THEN
    MAP_EVERY (fun t -> MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC t)
     [`a:real^N`; `b:real^N`] THEN
    DISCH_THEN(fun th -> X_GEN_TAC `x:real^N` THEN STRIP_TAC THEN
                         MP_TAC(SPEC `inv(c) % x:real^N` th)) THEN
    ASM_REWRITE_TAC[VECTOR_MUL_COMPONENT; IN_IMAGE] THEN ANTS_TAC THENL
     [X_GEN_TAC `i:num` THEN STRIP_TAC THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `i:num`) THEN ASM_REWRITE_TAC[] THEN
      ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN REWRITE_TAC[GSYM real_div] THEN
      FIRST_X_ASSUM(DISJ_CASES_TAC o MATCH_MP (REAL_ARITH
       `~(c = &0) ==> &0 < c \/ &0 < --c`)) THEN
      ASM_SIMP_TAC[REAL_LE_RDIV_EQ; REAL_LE_LDIV_EQ] THEN
      GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [GSYM REAL_LE_NEG2] THEN
      ASM_SIMP_TAC[GSYM REAL_MUL_RNEG; GSYM REAL_LE_RDIV_EQ; GSYM
                   REAL_LE_LDIV_EQ] THEN
      REWRITE_TAC[real_div; REAL_INV_NEG] THEN REAL_ARITH_TAC;
      DISCH_TAC THEN EXISTS_TAC `inv c % x:real^N` THEN
      ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_RINV; VECTOR_MUL_LID]]]);;


let IS_INTERVAL_SCALING_EQ = 
prove
 (`!s:real^N->bool c.
        is_interval(IMAGE (\x. c % x) s) <=> c = &0 \/ is_interval s`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `c = &0` THENL
   [ASM_REWRITE_TAC[VECTOR_MUL_LZERO] THEN
    SUBGOAL_THEN `IMAGE ((\x. vec 0):real^N->real^N) s = {} \/
                  IMAGE ((\x. vec 0):real^N->real^N) s = {vec 0}`
    STRIP_ASSUME_TAC THENL
     [SET_TAC[];
      ASM_REWRITE_TAC[IS_INTERVAL_EMPTY];
      ASM_REWRITE_TAC[IS_INTERVAL_SING]];
    ASM_REWRITE_TAC[] THEN EQ_TAC THEN REWRITE_TAC[IS_INTERVAL_SCALING] THEN
    DISCH_THEN(MP_TAC o SPEC `inv c:real` o MATCH_MP IS_INTERVAL_SCALING) THEN
    ASM_SIMP_TAC[GSYM IMAGE_o; VECTOR_MUL_ASSOC; o_DEF; REAL_MUL_LINV;
                 VECTOR_MUL_LID; IMAGE_ID]]);;


let lemma = 
prove
 (`!c. &0 < c
       ==> !s:real^N->bool. is_interval(IMAGE (\x. c % x) s) <=>
                            is_interval s`,

  SIMP_TAC[IS_INTERVAL_SCALING_EQ; REAL_LT_IMP_NZ]) in
add_scaling_theorems [lemma];;

(* ------------------------------------------------------------------------- *)
(* Line segments, with same open/closed overloading as for intervals.        *)
(* ------------------------------------------------------------------------- *)


let closed_segment = define
 `closed_segment[a,b] = {(&1 - u) % a + u % b | &0 <= u /\ u <= &1}`;;


let open_segment = new_definition
 `open_segment(a,b) = closed_segment[a,b] DIFF {a,b}`;;


let OPEN_SEGMENT_ALT = 
prove
 (`!a b:real^N.
        ~(a = b)
        ==> open_segment(a,b) = {(&1 - u) % a + u % b | &0 < u /\ u < &1}`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[open_segment; closed_segment] THEN
  REWRITE_TAC[EXTENSION; IN_DIFF; IN_INSERT; NOT_IN_EMPTY; IN_ELIM_THM] THEN
  X_GEN_TAC `x:real^N` THEN REWRITE_TAC[LEFT_AND_EXISTS_THM] THEN
  AP_TERM_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN
  X_GEN_TAC `u:real` THEN ASM_CASES_TAC `x:real^N = (&1 - u) % a + u % b` THEN
  ASM_REWRITE_TAC[REAL_LE_LT;
    VECTOR_ARITH `(&1 - u) % a + u % b = a <=> u % (b - a) = vec 0`;
    VECTOR_ARITH `(&1 - u) % a + u % b = b <=> (&1 - u) % (b - a) = vec 0`;
    VECTOR_MUL_EQ_0; REAL_SUB_0; VECTOR_SUB_EQ] THEN
  REAL_ARITH_TAC);;

make_overloadable "segment" `:A`;;

overload_interface("segment",`open_segment`);;
overload_interface("segment",`closed_segment`);;


let segment = 
prove
 (`segment[a,b] = {(&1 - u) % a + u % b | &0 <= u /\ u <= &1} /\
   segment(a,b) = segment[a,b] DIFF {a,b}`,

  REWRITE_TAC[open_segment; closed_segment]);;


let SEGMENT_REFL = 
prove
 (`(!a. segment[a,a] = {a}) /\
   (!a. segment(a,a) = {})`,

  REWRITE_TAC[segment; VECTOR_ARITH `(&1 - u) % a + u % a = a`] THEN
  SET_TAC[REAL_POS]);;


let IN_SEGMENT = 
prove
 (`!a b x:real^N.
        (x IN segment[a,b] <=>
         ?u. &0 <= u /\ u <= &1 /\ x = (&1 - u) % a + u % b) /\
        (x IN segment(a,b) <=>
         ~(a = b) /\ ?u. &0 < u /\ u < &1 /\ x = (&1 - u) % a + u % b)`,

  REPEAT STRIP_TAC THENL
   [REWRITE_TAC[segment; IN_ELIM_THM; CONJ_ASSOC]; ALL_TAC] THEN
  ASM_CASES_TAC `a:real^N = b` THEN
  ASM_REWRITE_TAC[SEGMENT_REFL; NOT_IN_EMPTY] THEN
  ASM_SIMP_TAC[OPEN_SEGMENT_ALT; IN_ELIM_THM; CONJ_ASSOC]);;


let SEGMENT_SYM = 
prove
 (`(!a b:real^N. segment[a,b] = segment[b,a]) /\
   (!a b:real^N. segment(a,b) = segment(b,a))`,

  MATCH_MP_TAC(TAUT `a /\ (a ==> b) ==> a /\ b`) THEN
  SIMP_TAC[open_segment] THEN
  CONJ_TAC THENL [ALL_TAC; SIMP_TAC[INSERT_AC]] THEN
  REWRITE_TAC[EXTENSION; IN_SEGMENT] THEN REPEAT GEN_TAC THEN EQ_TAC THEN
  DISCH_THEN(X_CHOOSE_TAC `u:real`) THEN EXISTS_TAC `&1 - u` THEN
  ASM_REWRITE_TAC[] THEN
  REPEAT CONJ_TAC THEN TRY ASM_ARITH_TAC THEN VECTOR_ARITH_TAC);;


let ENDS_IN_SEGMENT = 
prove
 (`!a b. a IN segment[a,b] /\ b IN segment[a,b]`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[segment; IN_ELIM_THM] THENL
   [EXISTS_TAC `&0`; EXISTS_TAC `&1`] THEN
  (CONJ_TAC THENL [REAL_ARITH_TAC; VECTOR_ARITH_TAC]));;


let ENDS_NOT_IN_SEGMENT = 
prove
 (`!a b. ~(a IN segment(a,b)) /\ ~(b IN segment(a,b))`,

  REWRITE_TAC[open_segment] THEN SET_TAC[]);;


let SEGMENT_CLOSED_OPEN = 
prove
 (`!a b. segment[a,b] = segment(a,b) UNION {a,b}`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_segment] THEN MATCH_MP_TAC(SET_RULE
   `a IN s /\ b IN s ==> s = (s DIFF {a,b}) UNION {a,b}`) THEN
  REWRITE_TAC[ENDS_IN_SEGMENT]);;


let MIDPOINT_IN_SEGMENT = 
prove
 (`(!a b:real^N. midpoint(a,b) IN segment[a,b]) /\
   (!a b:real^N. midpoint(a,b) IN segment(a,b) <=> ~(a = b))`,

  REWRITE_TAC[IN_SEGMENT] THEN REPEAT STRIP_TAC THENL
   [ALL_TAC; ASM_CASES_TAC `a:real^N = b` THEN ASM_REWRITE_TAC[]] THEN
  EXISTS_TAC `&1 / &2` THEN REWRITE_TAC[midpoint] THEN
  CONV_TAC REAL_RAT_REDUCE_CONV THEN VECTOR_ARITH_TAC);;


let BETWEEN_IN_SEGMENT = 
prove
 (`!x a b:real^N. between x (a,b) <=> x IN segment[a,b]`,

  REPEAT GEN_TAC THEN REWRITE_TAC[between] THEN
  ASM_CASES_TAC `a:real^N = b` THEN
  ASM_REWRITE_TAC[SEGMENT_REFL; IN_SING] THENL [NORM_ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[segment; IN_ELIM_THM] THEN EQ_TAC THENL
   [DISCH_THEN(ASSUME_TAC o SYM) THEN
    EXISTS_TAC `dist(a:real^N,x) / dist(a,b)` THEN
    ASM_SIMP_TAC[REAL_LE_LDIV_EQ; REAL_LE_RDIV_EQ; DIST_POS_LT] THEN CONJ_TAC
    THENL [FIRST_ASSUM(SUBST1_TAC o SYM) THEN NORM_ARITH_TAC; ALL_TAC] THEN
    MATCH_MP_TAC VECTOR_MUL_LCANCEL_IMP THEN EXISTS_TAC `dist(a:real^N,b)` THEN
    ASM_SIMP_TAC[VECTOR_MUL_ASSOC; VECTOR_ADD_LDISTRIB; REAL_SUB_LDISTRIB;
                 REAL_DIV_LMUL; DIST_EQ_0] THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [DIST_TRIANGLE_EQ] o SYM) THEN
    FIRST_ASSUM(SUBST1_TAC o SYM) THEN
    REWRITE_TAC[dist; REAL_ARITH `(a + b) * &1 - a = b`] THEN
    VECTOR_ARITH_TAC;
    STRIP_TAC THEN ASM_REWRITE_TAC[dist] THEN
    REWRITE_TAC[VECTOR_ARITH `a - ((&1 - u) % a + u % b) = u % (a - b)`;
                VECTOR_ARITH `((&1 - u) % a + u % b) - b = (&1 - u) % (a - b)`;
                NORM_MUL; GSYM REAL_ADD_LDISTRIB] THEN
    REPEAT(POP_ASSUM MP_TAC) THEN CONV_TAC REAL_FIELD]);;


let IN_SEGMENT_COMPONENT = 
prove
 (`!a b x:real^N i.
        x IN segment[a,b] /\ 1 <= i /\ i <= dimindex(:N)
        ==> min (a$i) (b$i) <= x$i /\ x$i <= max (a$i) (b$i)`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [IN_SEGMENT]) THEN
  DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
  FIRST_X_ASSUM(X_CHOOSE_THEN `t:real` STRIP_ASSUME_TAC) THEN
  ASM_REWRITE_TAC[VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT] THEN
  SIMP_TAC[REAL_ARITH `c <= u * a + t * b <=> u * --a + t * --b <= --c`] THEN
  MATCH_MP_TAC REAL_CONVEX_BOUND_LE THEN ASM_REAL_ARITH_TAC);;


let SEGMENT_1 = 
prove
 (`(!a b. segment[a,b] =
          if drop a <= drop b then interval[a,b] else interval[b,a]) /\
   (!a b. segment(a,b) =
          if drop a <= drop b then interval(a,b) else interval(b,a))`,

  CONJ_TAC THEN REPEAT GEN_TAC THEN REWRITE_TAC[open_segment] THEN
  COND_CASES_TAC THEN
  REWRITE_TAC[IN_DIFF; IN_INSERT; NOT_IN_EMPTY;
              EXTENSION; GSYM BETWEEN_IN_SEGMENT; between; IN_INTERVAL_1] THEN
  REWRITE_TAC[GSYM DROP_EQ; DIST_REAL; GSYM drop] THEN ASM_REAL_ARITH_TAC);;


let OPEN_SEGMENT_1 = 
prove
 (`!a b:real^1. open(segment(a,b))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[SEGMENT_1] THEN
  COND_CASES_TAC THEN REWRITE_TAC[OPEN_INTERVAL]);;


let SEGMENT_TRANSLATION = 
prove
 (`(!c a b. segment[c + a,c + b] = IMAGE (\x. c + x) (segment[a,b])) /\
   (!c a b. segment(c + a,c + b) = IMAGE (\x. c + x) (segment(a,b)))`,

  REWRITE_TAC[EXTENSION; IN_SEGMENT; IN_IMAGE] THEN
  REWRITE_TAC[VECTOR_ARITH `(&1 - u) % (c + a) + u % (c + b) =
                            c + (&1 - u) % a + u % b`] THEN
  REWRITE_TAC[VECTOR_ARITH `c + a:real^N = c + b <=> a = b`] THEN
  MESON_TAC[]);;

add_translation_invariants
 [CONJUNCT1 SEGMENT_TRANSLATION; CONJUNCT2 SEGMENT_TRANSLATION];;


let CLOSED_SEGMENT_LINEAR_IMAGE = 
prove
 (`!f a b. linear f
           ==> segment[f a,f b] = IMAGE f (segment[a,b])`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[EXTENSION; IN_IMAGE; IN_SEGMENT] THEN
  FIRST_ASSUM(fun th -> REWRITE_TAC[GSYM(MATCH_MP LINEAR_CMUL th)]) THEN
  FIRST_ASSUM(fun th -> REWRITE_TAC[GSYM(MATCH_MP LINEAR_ADD th)]) THEN
  MESON_TAC[]);;

add_linear_invariants [CLOSED_SEGMENT_LINEAR_IMAGE];;


let OPEN_SEGMENT_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N a b.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> segment(f a,f b) = IMAGE f (segment(a,b))`,

  REWRITE_TAC[open_segment] THEN GEOM_TRANSFORM_TAC[]);;

add_linear_invariants [OPEN_SEGMENT_LINEAR_IMAGE];;


let IN_OPEN_SEGMENT = 
prove
 (`!a b x:real^N.
        x IN segment(a,b) <=> x IN segment[a,b] /\ ~(x = a) /\ ~(x = b)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[open_segment; IN_DIFF] THEN SET_TAC[]);;


let IN_OPEN_SEGMENT_ALT = 
prove
 (`!a b x:real^N.
        x IN segment(a,b) <=>
        x IN segment[a,b] /\ ~(x = a) /\ ~(x = b) /\ ~(a = b)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `a:real^N = b` THEN
  ASM_REWRITE_TAC[SEGMENT_REFL; IN_SING; NOT_IN_EMPTY] THEN
  ASM_MESON_TAC[IN_OPEN_SEGMENT]);;


let COLLINEAR_DIST_IN_CLOSED_SEGMENT = 
prove
 (`!a b x. collinear {x,a,b} /\
           dist(x,a) <= dist(a,b) /\ dist(x,b) <= dist(a,b)
           ==> x IN segment[a,b]`,


let COLLINEAR_DIST_IN_OPEN_SEGMENT = 
prove
 (`!a b x. collinear {x,a,b} /\
           dist(x,a) < dist(a,b) /\ dist(x,b) < dist(a,b)
           ==> x IN segment(a,b)`,


let SEGMENT_SCALAR_MULTIPLE = 
prove
 (`(!a b v. segment[a % v,b % v] =
            {x % v:real^N | a <= x /\ x <= b \/ b <= x /\ x <= a}) /\
   (!a b v. ~(v = vec 0)
            ==> segment(a % v,b % v) =
                {x % v:real^N | a < x /\ x < b \/ b < x /\ x < a})`,

  MATCH_MP_TAC(TAUT `a /\ (a ==> b) ==> a /\ b`) THEN REPEAT STRIP_TAC THENL
   [REPEAT GEN_TAC THEN
    MP_TAC(SPECL [`a % basis 1:real^1`; `b % basis 1:real^1`]
     (CONJUNCT1 SEGMENT_1)) THEN
    REWRITE_TAC[segment; VECTOR_MUL_ASSOC; GSYM VECTOR_ADD_RDISTRIB] THEN
    REWRITE_TAC[SET_RULE `{f x % b | p x} = IMAGE (\a. a % b) {f x | p x}`] THEN
    DISCH_TAC THEN AP_TERM_TAC THEN
    FIRST_X_ASSUM(MP_TAC o AP_TERM `IMAGE drop`) THEN
    REWRITE_TAC[GSYM IMAGE_o; o_DEF; DROP_CMUL] THEN
    SIMP_TAC[drop; BASIS_COMPONENT; DIMINDEX_GE_1; LE_REFL] THEN
    REWRITE_TAC[REAL_MUL_RID; IMAGE_ID] THEN DISCH_THEN SUBST1_TAC THEN
    MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
    CONJ_TAC THENL [MESON_TAC[LIFT_DROP]; ALL_TAC] THEN
    REWRITE_TAC[FORALL_LIFT; LIFT_DROP] THEN GEN_TAC THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[IN_INTERVAL_1; LIFT_DROP] THEN
    SIMP_TAC[drop; VECTOR_MUL_COMPONENT; BASIS_COMPONENT; DIMINDEX_GE_1;
             LE_REFL; IN_ELIM_THM] THEN ASM_REAL_ARITH_TAC;
    ASM_REWRITE_TAC[open_segment] THEN
    ASM_SIMP_TAC[VECTOR_MUL_RCANCEL; SET_RULE
     `(!x y. x % v = y % v <=> x = y)
      ==> {x % v | P x} DIFF {a % v,b % v} =
          {x % v | P x /\ ~(x = a) /\ ~(x = b)}`] THEN
    ONCE_REWRITE_TAC[SIMPLE_IMAGE_GEN] THEN AP_TERM_TAC THEN
    REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN REAL_ARITH_TAC]);;


let FINITE_INTER_COLLINEAR_OPEN_SEGMENTS = 
prove
 (`!a b c d:real^N.
        collinear{a,b,c}
        ==> (FINITE(segment(a,b) INTER segment(c,d)) <=>
             segment(a,b) INTER segment(c,d) = {})`,

  REPEAT GEN_TAC THEN ABBREV_TAC `m:real^N = b - a` THEN POP_ASSUM MP_TAC THEN
  GEOM_NORMALIZE_TAC `m:real^N` THEN
  SIMP_TAC[VECTOR_SUB_EQ; SEGMENT_REFL; INTER_EMPTY; FINITE_EMPTY] THEN
  X_GEN_TAC `m:real^N` THEN DISCH_TAC THEN REPEAT GEN_TAC THEN
  DISCH_THEN(SUBST_ALL_TAC o SYM) THEN POP_ASSUM MP_TAC THEN
  GEOM_ORIGIN_TAC `a:real^N` THEN GEOM_BASIS_MULTIPLE_TAC 1 `b:real^N` THEN
  X_GEN_TAC `b:real` THEN DISCH_TAC THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `y:real^N`] THEN
  SIMP_TAC[VECTOR_SUB_RZERO; NORM_MUL; NORM_BASIS; DIMINDEX_GE_1; LE_REFL] THEN
  ASM_REWRITE_TAC[real_abs; REAL_MUL_RID] THEN DISCH_THEN SUBST_ALL_TAC THEN
  POP_ASSUM(K ALL_TAC) THEN
  ASM_CASES_TAC `collinear{vec 0:real^N,&1 % basis 1,y}` THENL
   [POP_ASSUM MP_TAC THEN
    SIMP_TAC[COLLINEAR_LEMMA_ALT; BASIS_NONZERO; DIMINDEX_GE_1; LE_REFL] THEN
    MATCH_MP_TAC(TAUT
     `~a /\ (b ==> c ==> d) ==> a \/ b ==> a \/ c ==> d`) THEN
    CONJ_TAC THENL
     [SIMP_TAC[VECTOR_MUL_LID; BASIS_NONZERO; DIMINDEX_GE_1; LE_REFL];
      REWRITE_TAC[LEFT_IMP_EXISTS_THM]] THEN
    X_GEN_TAC `b:real` THEN DISCH_THEN SUBST_ALL_TAC THEN
    X_GEN_TAC `a:real` THEN DISCH_THEN SUBST_ALL_TAC THEN
    REWRITE_TAC[VECTOR_MUL_ASSOC; REAL_MUL_RID] THEN
    SUBST1_TAC(VECTOR_ARITH `vec 0:real^N = &0 % basis 1`) THEN
    SIMP_TAC[SEGMENT_SCALAR_MULTIPLE; BASIS_NONZERO; DIMINDEX_GE_1; LE_REFL;
     VECTOR_MUL_RCANCEL; IMAGE_EQ_EMPTY; FINITE_IMAGE_INJ_EQ; SET_RULE
     `(!x y. x % v = y % v <=> x = y)
      ==> {x % v | P x} INTER {x % v | Q x} =
          IMAGE (\x. x % v) {x | P x /\ Q x}`] THEN
    REWRITE_TAC[REAL_ARITH `(&0 < x /\ x < &1 \/ &1 < x /\ x < &0) /\
                            (b < x /\ x < a \/ a < x /\ x < b) <=>
                       max (&0) (min a b) < x /\ x < min (&1) (max a b)`] THEN
    SIMP_TAC[FINITE_REAL_INTERVAL; EXTENSION; NOT_IN_EMPTY; IN_ELIM_THM] THEN
    SIMP_TAC[GSYM REAL_LT_BETWEEN; GSYM NOT_EXISTS_THM] THEN REAL_ARITH_TAC;
    DISCH_TAC THEN ASM_CASES_TAC
     `segment(vec 0:real^N,&1 % basis 1) INTER segment (x,y) = {}` THEN
    ASM_REWRITE_TAC[FINITE_EMPTY] THEN DISCH_THEN(K ALL_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    REWRITE_TAC[open_segment; IN_DIFF; NOT_IN_EMPTY;
                DE_MORGAN_THM; IN_INTER; IN_INSERT] THEN
    DISCH_THEN(X_CHOOSE_THEN `p:real^N` STRIP_ASSUME_TAC) THEN
    UNDISCH_TAC `~collinear{vec 0:real^N,&1 % basis 1, y}` THEN
    RULE_ASSUM_TAC(REWRITE_RULE[VECTOR_MUL_LID]) THEN
    REWRITE_TAC[VECTOR_MUL_LID] THEN
    MATCH_MP_TAC COLLINEAR_SUBSET THEN
    EXISTS_TAC `{p,x:real^N, y, vec 0, basis 1}` THEN
    CONJ_TAC THENL [ALL_TAC; SET_TAC[]] THEN
    MP_TAC(ISPECL [`{y:real^N,vec 0,basis 1}`; `p:real^N`; `x:real^N`]
        COLLINEAR_TRIPLES) THEN
    ASM_REWRITE_TAC[] THEN DISCH_THEN SUBST1_TAC THEN
    REWRITE_TAC[FORALL_IN_INSERT; NOT_IN_EMPTY] THEN CONJ_TAC THENL
     [ONCE_REWRITE_TAC[SET_RULE `{p,x,y} = {x,p,y}`] THEN
      MATCH_MP_TAC BETWEEN_IMP_COLLINEAR THEN
      ASM_REWRITE_TAC[BETWEEN_IN_SEGMENT];
      ALL_TAC] THEN
    ASM_SIMP_TAC[GSYM COLLINEAR_4_3] THEN
    ONCE_REWRITE_TAC[SET_RULE `{p,x,z,w} = {w,z,p,x}`] THEN
    SIMP_TAC[COLLINEAR_4_3; BASIS_NONZERO; DIMINDEX_GE_1; ARITH] THEN
    REPEAT(FIRST_X_ASSUM(MP_TAC o MATCH_MP BETWEEN_IMP_COLLINEAR o
        GEN_REWRITE_RULE I [GSYM BETWEEN_IN_SEGMENT])) THEN
    REPEAT(POP_ASSUM MP_TAC) THEN SIMP_TAC[INSERT_AC]]);;

let DIST_IN_CLOSED_SEGMENT,DIST_IN_OPEN_SEGMENT = (CONJ_PAIR o prove)
 (`(!a b x:real^N.
    x IN segment[a,b] ==> dist(x,a) <= dist(a,b) /\ dist(x,b) <= dist(a,b)) /\
   (!a b x:real^N.
    x IN segment(a,b) ==> dist(x,a) < dist(a,b) /\ dist(x,b) < dist(a,b))`,
  SIMP_TAC[IN_SEGMENT; RIGHT_AND_EXISTS_THM; LEFT_IMP_EXISTS_THM; dist;
           VECTOR_ARITH
    `((&1 - u) % a + u % b) - a:real^N = u % (b - a) /\
     ((&1 - u) % a + u % b) - b = --(&1 - u) % (b - a)`] THEN
  REWRITE_TAC[NORM_MUL; REAL_ABS_NEG; NORM_SUB] THEN CONJ_TAC THEN
  REPEAT GEN_TAC THEN STRIP_TAC THENL
   [REWRITE_TAC[REAL_ARITH `x * y <= y <=> x * y <= &1 * y`] THEN
    CONJ_TAC THEN MATCH_MP_TAC REAL_LE_RMUL THEN
    REWRITE_TAC[NORM_POS_LE] THEN ASM_REAL_ARITH_TAC;
    REWRITE_TAC[REAL_ARITH `x * y < y <=> x * y < &1 * y`] THEN
    ASM_SIMP_TAC[REAL_LT_RMUL_EQ; NORM_POS_LT; VECTOR_SUB_EQ] THEN
    ASM_REAL_ARITH_TAC]);;


let DIST_DECREASES_OPEN_SEGMENT = 
prove
 (`!a b c x:real^N.
      x IN segment(a,b) ==> dist(c,x) < dist(c,a) \/ dist(c,x) < dist(c,b)`,

  GEOM_ORIGIN_TAC `a:real^N` THEN GEOM_NORMALIZE_TAC `b:real^N` THEN
  REWRITE_TAC[SEGMENT_REFL; NOT_IN_EMPTY] THEN X_GEN_TAC `b:real^N` THEN
  GEOM_BASIS_MULTIPLE_TAC 1 `b:real^N` THEN X_GEN_TAC `b:real` THEN
  SIMP_TAC[NORM_MUL; NORM_BASIS; real_abs; DIMINDEX_GE_1; LE_REFL;
           REAL_MUL_RID; VECTOR_MUL_LID] THEN
  REPEAT(DISCH_THEN(K ALL_TAC)) THEN REPEAT GEN_TAC THEN
  REWRITE_TAC[IN_SEGMENT; dist] THEN STRIP_TAC THEN
  ASM_REWRITE_TAC[VECTOR_MUL_RZERO; VECTOR_ADD_LID] THEN
  SUBGOAL_THEN
   `norm((c$1 - u) % basis 1:real^N) < norm((c:real^N)$1 % basis 1:real^N) \/
    norm((c$1 - u) % basis 1:real^N) < norm((c$1 - &1) % basis 1:real^N)`
  MP_TAC THENL
   [SIMP_TAC[NORM_MUL; NORM_BASIS; DIMINDEX_GE_1; LE_REFL] THEN
    ASM_REAL_ARITH_TAC;
    ASM_SIMP_TAC[NORM_LT; DOT_LMUL; DOT_RMUL; DOT_BASIS; DIMINDEX_GE_1;
              DOT_LSUB; DOT_RSUB; LE_REFL; VECTOR_MUL_COMPONENT; VEC_COMPONENT;
              BASIS_COMPONENT; DOT_LZERO; DOT_RZERO; VECTOR_SUB_COMPONENT] THEN
    ASM_REAL_ARITH_TAC]);;


let DIST_DECREASES_CLOSED_SEGMENT = 
prove
 (`!a b c x:real^N.
      x IN segment[a,b] ==> dist(c,x) <= dist(c,a) \/ dist(c,x) <= dist(c,b)`,

(* ------------------------------------------------------------------------- *)
(* Limit component bounds.                                                   *)
(* ------------------------------------------------------------------------- *)


let LIM_COMPONENT_UBOUND = 
prove
 (`!net:(A)net f (l:real^N) b k.
        ~(trivial_limit net) /\ (f --> l) net /\
        eventually (\x. (f x)$k <= b) net /\
        1 <= k /\ k <= dimindex(:N)
        ==> l$k <= b`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPECL
   [`net:(A)net`; `f:A->real^N`; `{y:real^N | basis k dot y <= b}`; `l:real^N`]
   LIM_IN_CLOSED_SET) THEN
  ASM_SIMP_TAC[CLOSED_HALFSPACE_LE; IN_ELIM_THM; DOT_BASIS]);;


let LIM_COMPONENT_LBOUND = 
prove
 (`!net:(A)net f (l:real^N) b k.
        ~(trivial_limit net) /\ (f --> l) net /\
        eventually (\x. b <= (f x)$k) net /\
        1 <= k /\ k <= dimindex(:N)
        ==> b <= l$k`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPECL
   [`net:(A)net`; `f:A->real^N`; `{y:real^N | b <= basis k dot y}`; `l:real^N`]
   LIM_IN_CLOSED_SET) THEN
  ASM_SIMP_TAC[REWRITE_RULE[real_ge] CLOSED_HALFSPACE_GE;
               IN_ELIM_THM; DOT_BASIS]);;


let LIM_COMPONENT_EQ = 
prove
 (`!net f:A->real^N i l b.
        (f --> l) net /\ 1 <= i /\ i <= dimindex(:N) /\
        ~(trivial_limit net) /\ eventually (\x. f(x)$i = b) net
        ==> l$i = b`,

  REWRITE_TAC[GSYM REAL_LE_ANTISYM; EVENTUALLY_AND] THEN
  MESON_TAC[LIM_COMPONENT_UBOUND; LIM_COMPONENT_LBOUND]);;


let LIM_COMPONENT_LE = 
prove
 (`!net:(A)net f:A->real^N g:A->real^N k l m.
         ~(trivial_limit net) /\ (f --> l) net /\ (g --> m) net /\
        eventually (\x. (f x)$k <= (g x)$k) net /\
        1 <= k /\ k <= dimindex(:N)
        ==> l$k <= m$k`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[GSYM REAL_SUB_LE] THEN
  REWRITE_TAC[GSYM VECTOR_SUB_COMPONENT; LIM_COMPONENT_LBOUND] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c ==> d <=> b /\ a ==> c ==> d`] THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIM_SUB) THEN POP_ASSUM MP_TAC THEN
  REWRITE_TAC[IMP_IMP; GSYM CONJ_ASSOC; LIM_COMPONENT_LBOUND]);;


let LIM_DROP_LE = 
prove
 (`!net:(A)net f g l m.
         ~(trivial_limit net) /\ (f --> l) net /\ (g --> m) net /\
        eventually (\x. drop(f x) <= drop(g x)) net
        ==> drop l <= drop m`,

  REWRITE_TAC[drop] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC(ISPEC `net:(A)net` LIM_COMPONENT_LE) THEN
  MAP_EVERY EXISTS_TAC [`f:A->real^1`; `g:A->real^1`] THEN
  ASM_REWRITE_TAC[DIMINDEX_1; LE_REFL]);;


let LIM_DROP_UBOUND = 
prove
 (`!net f:A->real^1 l b.
        (f --> l) net /\
        ~(trivial_limit net) /\ eventually (\x. drop(f x) <= b) net
        ==> drop l <= b`,

  SIMP_TAC[drop] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC LIM_COMPONENT_UBOUND THEN
  REWRITE_TAC[LE_REFL; DIMINDEX_1] THEN ASM_MESON_TAC[]);;


let LIM_DROP_LBOUND = 
prove
 (`!net f:A->real^1 l b.
        (f --> l) net /\
        ~(trivial_limit net) /\ eventually (\x. b <= drop(f x)) net
        ==> b <= drop l`,

  SIMP_TAC[drop] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC LIM_COMPONENT_LBOUND THEN
  REWRITE_TAC[LE_REFL; DIMINDEX_1] THEN ASM_MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Also extending closed bounds to closures.                                 *)
(* ------------------------------------------------------------------------- *)


let IMAGE_CLOSURE_SUBSET = 
prove
 (`!f (s:real^N->bool) (t:real^M->bool).
      f continuous_on closure s /\ closed t /\ IMAGE f s SUBSET t
      ==> IMAGE f (closure s) SUBSET t`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `closure s SUBSET {x | (f:real^N->real^M) x IN t}` MP_TAC
  THENL [MATCH_MP_TAC SUBSET_TRANS; SET_TAC []]  THEN
  EXISTS_TAC `{x | x IN closure s /\ (f:real^N->real^M) x IN t}` THEN
  CONJ_TAC THENL
  [MATCH_MP_TAC CLOSURE_MINIMAL; SET_TAC[]] THEN
  ASM_SIMP_TAC[CONTINUOUS_CLOSED_PREIMAGE; CLOSED_CLOSURE] THEN
  MP_TAC (ISPEC `s:real^N->bool` CLOSURE_SUBSET) THEN ASM SET_TAC[]);;


let CLOSURE_IMAGE_CLOSURE = 
prove
 (`!f:real^M->real^N s.
        f continuous_on closure s
        ==> closure(IMAGE f (closure s)) = closure(IMAGE f s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM SUBSET_ANTISYM_EQ] THEN
  SIMP_TAC[SUBSET_CLOSURE; IMAGE_SUBSET; CLOSURE_SUBSET] THEN
  SIMP_TAC[CLOSURE_MINIMAL_EQ; CLOSED_CLOSURE] THEN
  MATCH_MP_TAC IMAGE_CLOSURE_SUBSET THEN
  ASM_REWRITE_TAC[CLOSED_CLOSURE; CLOSURE_SUBSET]);;


let CLOSURE_IMAGE_BOUNDED = 
prove
 (`!f:real^M->real^N s.
        f continuous_on closure s /\ bounded s
        ==> closure(IMAGE f s) = IMAGE f (closure s)`,

  REPEAT STRIP_TAC THEN
  TRANS_TAC EQ_TRANS `closure(IMAGE (f:real^M->real^N) (closure s))` THEN
  CONJ_TAC THENL [ASM_MESON_TAC[CLOSURE_IMAGE_CLOSURE]; ALL_TAC] THEN
  MATCH_MP_TAC CLOSURE_CLOSED THEN MATCH_MP_TAC COMPACT_IMP_CLOSED THEN
  MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
  ASM_REWRITE_TAC[COMPACT_CLOSURE]);;


let CONTINUOUS_ON_CLOSURE_NORM_LE = 
prove
 (`!f:real^N->real^M s x b.
      f continuous_on (closure s) /\
      (!y. y IN s ==> norm(f y) <= b) /\
      x IN (closure s)
      ==> norm(f x) <= b`,

  REWRITE_TAC [GSYM IN_CBALL_0] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^N->real^M) (closure s) SUBSET cball(vec 0,b)`
    MP_TAC THENL
  [MATCH_MP_TAC IMAGE_CLOSURE_SUBSET; ASM SET_TAC []] THEN
  ASM_REWRITE_TAC [CLOSED_CBALL] THEN ASM SET_TAC []);;


let CONTINUOUS_ON_CLOSURE_COMPONENT_LE = 
prove
 (`!f:real^N->real^M s x b k.
      f continuous_on (closure s) /\
      (!y. y IN s ==> (f y)$k <= b) /\
      x IN (closure s)
      ==> (f x)$k <= b`,

  REWRITE_TAC [GSYM IN_CBALL_0] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^N->real^M) (closure s) SUBSET {x | x$k <= b}`
  MP_TAC THENL
   [MATCH_MP_TAC IMAGE_CLOSURE_SUBSET; ASM SET_TAC []] THEN
  ASM_REWRITE_TAC[CLOSED_HALFSPACE_COMPONENT_LE] THEN ASM SET_TAC[]);;


let CONTINUOUS_ON_CLOSURE_COMPONENT_GE = 
prove
 (`!f:real^N->real^M s x b k.
      f continuous_on (closure s) /\
      (!y. y IN s ==> b <= (f y)$k) /\
      x IN (closure s)
      ==> b <= (f x)$k`,

  REWRITE_TAC [GSYM IN_CBALL_0] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^N->real^M) (closure s) SUBSET {x | x$k >= b}`
  MP_TAC THENL
   [MATCH_MP_TAC IMAGE_CLOSURE_SUBSET; ASM SET_TAC [real_ge]] THEN
  ASM_REWRITE_TAC[CLOSED_HALFSPACE_COMPONENT_GE] THEN ASM SET_TAC[real_ge]);;

(* ------------------------------------------------------------------------- *)
(* Limits relative to a union.                                               *)
(* ------------------------------------------------------------------------- *)


let LIM_WITHIN_UNION = 
prove
 (`(f --> l) (at x within (s UNION t)) <=>
   (f --> l) (at x within s) /\ (f --> l) (at x within t)`,

  REWRITE_TAC[LIM_WITHIN; IN_UNION; AND_FORALL_THM] THEN
  AP_TERM_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  EQ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN DISCH_THEN
   (CONJUNCTS_THEN2 (X_CHOOSE_TAC `d:real`) (X_CHOOSE_TAC `k:real`)) THEN
  EXISTS_TAC `min d k` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  ASM_MESON_TAC[]);;


let CONTINUOUS_ON_UNION = 
prove
 (`!f s t. closed s /\ closed t /\ f continuous_on s /\ f continuous_on t
           ==> f continuous_on (s UNION t)`,


let CONTINUOUS_ON_CASES = 
prove
 (`!P f g:real^M->real^N s t.
        closed s /\ closed t /\ f continuous_on s /\ g continuous_on t /\
        (!x. x IN s /\ ~P x \/ x IN t /\ P x ==> f x = g x)
        ==> (\x. if P x then f x else g x) continuous_on (s UNION t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_UNION THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_EQ THENL
   [EXISTS_TAC `f:real^M->real^N`; EXISTS_TAC `g:real^M->real^N`] THEN
  ASM_REWRITE_TAC[] THEN ASM_MESON_TAC[]);;


let CONTINUOUS_ON_UNION_LOCAL = 
prove
 (`!f:real^M->real^N s.
        closed_in (subtopology euclidean (s UNION t)) s /\
        closed_in (subtopology euclidean (s UNION t)) t /\
        f continuous_on s /\ f continuous_on t
        ==> f continuous_on (s UNION t)`,


let CONTINUOUS_ON_CASES_LOCAL = 
prove
 (`!P f g:real^M->real^N s t.
        closed_in (subtopology euclidean (s UNION t)) s /\
        closed_in (subtopology euclidean (s UNION t)) t /\
        f continuous_on s /\ g continuous_on t /\
        (!x. x IN s /\ ~P x \/ x IN t /\ P x ==> f x = g x)
        ==> (\x. if P x then f x else g x) continuous_on (s UNION t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_UNION_LOCAL THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_EQ THENL
   [EXISTS_TAC `f:real^M->real^N`; EXISTS_TAC `g:real^M->real^N`] THEN
  ASM_REWRITE_TAC[] THEN ASM_MESON_TAC[]);;


let CONTINUOUS_ON_CASES_LE = 
prove
 (`!f g:real^M->real^N h s a.
        f continuous_on {t | t IN s /\ h t <= a} /\
        g continuous_on {t | t IN s /\ a <= h t} /\
        (lift o h) continuous_on s /\
        (!t. t IN s /\ h t = a ==> f t = g t)
        ==> (\t. if h t <= a then f(t) else g(t)) continuous_on s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_SUBSET THEN EXISTS_TAC
   `{t | t IN s /\ (h:real^M->real) t <= a} UNION
    {t | t IN s /\ a <= h t}` THEN
  CONJ_TAC THENL
   [ALL_TAC; SIMP_TAC[SUBSET; IN_UNION; IN_ELIM_THM; REAL_LE_TOTAL]] THEN
  MATCH_MP_TAC CONTINUOUS_ON_CASES_LOCAL THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[IN_ELIM_THM; GSYM CONJ_ASSOC; REAL_LE_ANTISYM] THEN
  REWRITE_TAC[CONJ_ASSOC] THEN CONJ_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[]] THEN
  CONJ_TAC THENL
   [SUBGOAL_THEN
     `{t | t IN s /\ (h:real^M->real) t <= a} =
      {t | t IN ({t | t IN s /\ h t <= a} UNION {t | t IN s /\ a <= h t}) /\
           (lift o h) t IN {x | x$1 <= a}}`
     (fun th -> GEN_REWRITE_TAC RAND_CONV [th])
    THENL
     [REWRITE_TAC[GSYM drop; o_THM; IN_ELIM_THM; LIFT_DROP; EXTENSION;
                  IN_UNION] THEN
      GEN_TAC THEN EQ_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
      ASM_REAL_ARITH_TAC;
      MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE THEN
      ASM_REWRITE_TAC[CLOSED_HALFSPACE_COMPONENT_LE; ETA_AX] THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        CONTINUOUS_ON_SUBSET)) THEN
      SET_TAC[]];
    SUBGOAL_THEN
     `{t | t IN s /\ a <= (h:real^M->real) t} =
      {t | t IN ({t | t IN s /\ h t <= a} UNION {t | t IN s /\ a <= h t}) /\
           (lift o h) t IN {x | x$1 >= a}}`
     (fun th -> GEN_REWRITE_TAC RAND_CONV [th])
    THENL
     [REWRITE_TAC[GSYM drop; o_THM; IN_ELIM_THM; LIFT_DROP; EXTENSION;
                  IN_UNION] THEN
      GEN_TAC THEN EQ_TAC THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
      ASM_REAL_ARITH_TAC;
      MATCH_MP_TAC CONTINUOUS_CLOSED_IN_PREIMAGE THEN
      ASM_REWRITE_TAC[CLOSED_HALFSPACE_COMPONENT_GE; ETA_AX] THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        CONTINUOUS_ON_SUBSET)) THEN
      SET_TAC[]]]);;


let CONTINUOUS_ON_CASES_1 = 
prove
 (`!f g:real^1->real^N s a.
        f continuous_on {t | t IN s /\ drop t <= a} /\
        g continuous_on {t | t IN s /\ a <= drop t} /\
        (lift a IN s ==> f(lift a) = g(lift a))
        ==> (\t. if drop t <= a then f(t) else g(t)) continuous_on s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_CASES_LE THEN
  ASM_REWRITE_TAC[o_DEF; LIFT_DROP; CONTINUOUS_ON_ID] THEN
  REWRITE_TAC[GSYM LIFT_EQ; LIFT_DROP] THEN ASM_MESON_TAC[]);;


let EXTENSION_FROM_CLOPEN = 
prove
 (`!f:real^M->real^N s t u.
        open_in (subtopology euclidean s) t /\
        closed_in (subtopology euclidean s) t /\
        f continuous_on t /\ IMAGE f t SUBSET u /\ (u = {} ==> s = {})
        ==> ?g. g continuous_on s /\ IMAGE g s SUBSET u /\
                !x. x IN t ==> g x = f x`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `u:real^N->bool = {}` THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_EMPTY; IMAGE_CLAUSES; SUBSET_EMPTY;
               IMAGE_EQ_EMPTY; NOT_IN_EMPTY] THEN
  STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
  DISCH_THEN(X_CHOOSE_TAC `a:real^N`) THEN
  EXISTS_TAC `\x. if x IN t then (f:real^M->real^N) x else a` THEN
  SIMP_TAC[SUBSET; FORALL_IN_IMAGE] THEN
  CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
  SUBGOAL_THEN `s:real^M->bool = t UNION (s DIFF t)` SUBST1_TAC THENL
   [ASM SET_TAC[]; MATCH_MP_TAC CONTINUOUS_ON_CASES_LOCAL] THEN
  ASM_SIMP_TAC[SET_RULE `t SUBSET s ==> t UNION (s DIFF t) = s`] THEN
  REWRITE_TAC[CONTINUOUS_ON_CONST; IN_DIFF] THEN
  CONJ_TAC THENL [MATCH_MP_TAC CLOSED_IN_DIFF; MESON_TAC[]] THEN
  ASM_REWRITE_TAC[CLOSED_IN_REFL]);;

(* ------------------------------------------------------------------------- *)
(* Componentwise limits and continuity.                                      *)
(* ------------------------------------------------------------------------- *)


let LIM_COMPONENTWISE_LIFT = 
prove
 (`!net f:A->real^N.
        (f --> l) net <=>
        !i. 1 <= i /\ i <= dimindex(:N)
            ==> ((\x. lift((f x)$i)) --> lift(l$i)) net`,

  REPEAT GEN_TAC THEN REWRITE_TAC[tendsto] THEN EQ_TAC THENL
   [DISCH_TAC THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    X_GEN_TAC `e:real` THEN
    DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `e:real`) THEN
    ASM_SIMP_TAC[GSYM VECTOR_SUB_COMPONENT] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
    GEN_TAC THEN REWRITE_TAC[dist] THEN MATCH_MP_TAC(REAL_ARITH
     `y <= x ==> x < e ==> y < e`) THEN
    ASM_SIMP_TAC[COMPONENT_LE_NORM; GSYM LIFT_SUB; NORM_LIFT;
                 GSYM VECTOR_SUB_COMPONENT];
    GEN_REWRITE_TAC (LAND_CONV o BINDER_CONV) [RIGHT_IMP_FORALL_THM] THEN
    ONCE_REWRITE_TAC[IMP_IMP] THEN ONCE_REWRITE_TAC[IMP_CONJ_ALT] THEN
    ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN
    REWRITE_TAC[GSYM IN_NUMSEG; RIGHT_FORALL_IMP_THM] THEN
    SIMP_TAC[FORALL_EVENTUALLY; FINITE_NUMSEG; NUMSEG_EMPTY;
             GSYM NOT_LE; DIMINDEX_GE_1] THEN
    REWRITE_TAC[DIST_LIFT; GSYM VECTOR_SUB_COMPONENT] THEN
    DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `e / &(dimindex(:N))`) THEN
    ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; LE_1; DIMINDEX_GE_1] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EVENTUALLY_MONO) THEN
    X_GEN_TAC `x:A` THEN SIMP_TAC[GSYM VECTOR_SUB_COMPONENT; dist] THEN
    DISCH_TAC THEN W(MP_TAC o PART_MATCH lhand NORM_LE_L1 o lhand o snd) THEN
    MATCH_MP_TAC(REAL_ARITH `s < e ==> n <= s ==> n < e`) THEN
    MATCH_MP_TAC SUM_BOUND_LT_GEN THEN
    ASM_SIMP_TAC[FINITE_NUMSEG; NUMSEG_EMPTY; GSYM NOT_LE; DIMINDEX_GE_1;
                 CARD_NUMSEG_1; GSYM IN_NUMSEG]]);;


let CONTINUOUS_COMPONENTWISE_LIFT = 
prove
 (`!net f:A->real^N.
        f continuous net <=>
        !i. 1 <= i /\ i <= dimindex(:N)
            ==> (\x. lift((f x)$i)) continuous net`,

  REWRITE_TAC[continuous; GSYM LIM_COMPONENTWISE_LIFT]);;


let CONTINUOUS_ON_COMPONENTWISE_LIFT = 
prove
 (`!f:real^M->real^N s.
        f continuous_on s <=>
        !i. 1 <= i /\ i <= dimindex(:N)
            ==> (\x. lift((f x)$i)) continuous_on s`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV)
   [CONTINUOUS_COMPONENTWISE_LIFT] THEN
  MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Some more convenient intermediate-value theorem formulations.             *)
(* ------------------------------------------------------------------------- *)


let CONNECTED_IVT_HYPERPLANE = 
prove
 (`!s x y:real^N a b.
        connected s /\
        x IN s /\ y IN s /\ a dot x <= b /\ b <= a dot y
        ==> ?z. z IN s /\ a dot z = b`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [connected]) THEN
  REWRITE_TAC[NOT_EXISTS_THM] THEN DISCH_THEN(MP_TAC o SPECL
   [`{x:real^N | a dot x < b}`; `{x:real^N | a dot x > b}`]) THEN
  REWRITE_TAC[OPEN_HALFSPACE_LT; OPEN_HALFSPACE_GT] THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN STRIP_TAC THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_INTER; NOT_IN_EMPTY; SUBSET;
              IN_UNION; REAL_LT_LE; real_gt] THEN
  ASM_MESON_TAC[REAL_LE_TOTAL; REAL_LE_ANTISYM]);;


let CONNECTED_IVT_COMPONENT = 
prove
 (`!s x y:real^N a k.
        connected s /\ x IN s /\ y IN s /\
        1 <= k /\ k <= dimindex(:N) /\ x$k <= a /\ a <= y$k
        ==> ?z. z IN s /\ z$k = a`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPECL
   [`s:real^N->bool`; `x:real^N`; `y:real^N`; `(basis k):real^N`;
    `a:real`] CONNECTED_IVT_HYPERPLANE) THEN
  ASM_SIMP_TAC[DOT_BASIS]);;

(* ------------------------------------------------------------------------- *)
(* Rather trivial observation that we can map any connected set on segment.  *)
(* ------------------------------------------------------------------------- *)


let MAPPING_CONNECTED_ONTO_SEGMENT = 
prove
 (`!s:real^M->bool a b:real^N.
        connected s /\ ~(?a. s SUBSET {a})
        ==> ?f. f continuous_on s /\ IMAGE f s = segment[a,b]`,

  REPEAT STRIP_TAC THEN FIRST_X_ASSUM(MP_TAC o MATCH_MP (SET_RULE
   `~(?a. s SUBSET {a}) ==> ?a b. a IN s /\ b IN s /\ ~(a = b)`)) THEN
  REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`u:real^M`; `v:real^M`] THEN STRIP_TAC THEN EXISTS_TAC
   `\x:real^M. a + dist(u,x) / (dist(u,x) + dist(v,x)) % (b - a:real^N)` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC CONTINUOUS_ON_ADD THEN REWRITE_TAC[CONTINUOUS_ON_CONST] THEN
    MATCH_MP_TAC CONTINUOUS_ON_MUL THEN SIMP_TAC[o_DEF; CONTINUOUS_ON_CONST];
    REWRITE_TAC[segment; VECTOR_ARITH
     `(&1 - u) % a + u % b:real^N = a + u % (b - a)`] THEN
    MATCH_MP_TAC(SET_RULE
     `IMAGE f s = {x | P x}
      ==> IMAGE (\x. a + f x % b) s = {a + u % b:real^N | P u}`) THEN
    REWRITE_TAC[GSYM SUBSET_ANTISYM_EQ; SUBSET; FORALL_IN_IMAGE] THEN
    ASM_SIMP_TAC[IN_ELIM_THM; REAL_LE_RDIV_EQ; REAL_LE_LDIV_EQ;
      NORM_ARITH `~(u:real^N = v) ==> &0 < dist(u,x) + dist(v,x)`] THEN
    CONJ_TAC THENL [CONV_TAC NORM_ARITH; REWRITE_TAC[IN_IMAGE]] THEN
    X_GEN_TAC `t:real` THEN STRIP_TAC THEN
    MP_TAC(ISPECL
     [`IMAGE (\x:real^M. lift(dist(u,x) / (dist(u,x) + dist(v,x)))) s`;
      `vec 0:real^1`; `vec 1:real^1`; `t:real`; `1`]
        CONNECTED_IVT_COMPONENT) THEN
    ASM_SIMP_TAC[VEC_COMPONENT; DIMINDEX_1; ARITH_LE] THEN
    REWRITE_TAC[EXISTS_IN_IMAGE; GSYM drop; LIFT_DROP] THEN
    ANTS_TAC THENL [REWRITE_TAC[IN_IMAGE]; MESON_TAC[]] THEN
    REPEAT CONJ_TAC THENL
     [MATCH_MP_TAC CONNECTED_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[];
      EXISTS_TAC `u:real^M` THEN ASM_REWRITE_TAC[DIST_REFL; real_div] THEN
      REWRITE_TAC[GSYM LIFT_NUM; LIFT_EQ] THEN REAL_ARITH_TAC;
      EXISTS_TAC `v:real^M` THEN ASM_REWRITE_TAC[DIST_REFL] THEN
      ASM_SIMP_TAC[REAL_DIV_REFL; DIST_EQ_0; REAL_ADD_RID] THEN
      REWRITE_TAC[GSYM LIFT_NUM; LIFT_EQ]]] THEN
  REWRITE_TAC[real_div; LIFT_CMUL] THEN
  MATCH_MP_TAC CONTINUOUS_ON_MUL THEN
  REWRITE_TAC[CONTINUOUS_ON_LIFT_DIST] THEN
  MATCH_MP_TAC(REWRITE_RULE[o_DEF] CONTINUOUS_ON_INV) THEN
  ASM_SIMP_TAC[LIFT_ADD; NORM_ARITH
   `~(u:real^N = v) ==> ~(dist(u,x) + dist(v,x) = &0)`] THEN
  MATCH_MP_TAC CONTINUOUS_ON_ADD THEN
  REWRITE_TAC[REWRITE_RULE[o_DEF] CONTINUOUS_ON_LIFT_DIST]);;

(* ------------------------------------------------------------------------- *)
(* Also more convenient formulations of monotone convergence.                *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_INCREASING_CONVERGENT = 
prove
 (`!s:num->real^1.
        bounded {s n | n IN (:num)} /\ (!n. drop(s n) <= drop(s(SUC n)))
        ==> ?l. (s --> l) sequentially`,

  GEN_TAC THEN
  REWRITE_TAC[bounded; IN_ELIM_THM; ABS_DROP; LIM_SEQUENTIALLY; dist;
              DROP_SUB; IN_UNIV; GSYM EXISTS_DROP] THEN
  DISCH_TAC THEN MATCH_MP_TAC CONVERGENT_BOUNDED_MONOTONE THEN
  REWRITE_TAC[LEFT_EXISTS_AND_THM] THEN
  CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
  DISJ1_TAC THEN MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN
  ASM_REWRITE_TAC[REAL_LE_TRANS; REAL_LE_REFL]);;


let BOUNDED_DECREASING_CONVERGENT = 
prove
 (`!s:num->real^1.
        bounded {s n | n IN (:num)} /\ (!n. drop(s(SUC n)) <= drop(s(n)))
        ==> ?l. (s --> l) sequentially`,

  GEN_TAC THEN REWRITE_TAC[bounded; FORALL_IN_GSPEC] THEN
  DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
  MP_TAC(ISPEC `\n. --((s:num->real^1) n)` BOUNDED_INCREASING_CONVERGENT) THEN
  ASM_SIMP_TAC[bounded; FORALL_IN_GSPEC; NORM_NEG; DROP_NEG; REAL_LE_NEG2] THEN
  GEN_REWRITE_TAC (LAND_CONV o BINDER_CONV) [GSYM LIM_NEG_EQ] THEN
  REWRITE_TAC[VECTOR_NEG_NEG; ETA_AX] THEN MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Since we'll use some cardinality reasoning, add invariance theorems.      *)
(* ------------------------------------------------------------------------- *)

let card_translation_invariants = (CONJUNCTS o prove)
 (`(!a (s:real^N->bool) (t:A->bool).
     IMAGE (\x. a + x) s =_c t <=> s =_c t) /\
   (!a (s:A->bool) (t:real^N->bool).
     s =_c IMAGE (\x. a + x) t <=> s =_c t) /\
   (!a (s:real^N->bool) (t:A->bool).
     IMAGE (\x. a + x) s <_c t <=> s <_c t) /\
   (!a (s:A->bool) (t:real^N->bool).
     s <_c IMAGE (\x. a + x) t <=> s <_c t) /\
   (!a (s:real^N->bool) (t:A->bool).
     IMAGE (\x. a + x) s <=_c t <=> s <=_c t) /\
   (!a (s:A->bool) (t:real^N->bool).
     s <=_c IMAGE (\x. a + x) t <=> s <=_c t) /\
   (!a (s:real^N->bool) (t:A->bool).
     IMAGE (\x. a + x) s >_c t <=> s >_c t) /\
   (!a (s:A->bool) (t:real^N->bool).
     s >_c IMAGE (\x. a + x) t <=> s >_c t) /\
   (!a (s:real^N->bool) (t:A->bool).
     IMAGE (\x. a + x) s >=_c t <=> s >=_c t) /\
   (!a (s:A->bool) (t:real^N->bool).
     s >=_c IMAGE (\x. a + x) t <=> s >=_c t)`,
  REWRITE_TAC[gt_c; ge_c] THEN REPEAT STRIP_TAC THENL
   [MATCH_MP_TAC CARD_EQ_CONG;
    MATCH_MP_TAC CARD_EQ_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LE_CONG] THEN
  REWRITE_TAC[CARD_EQ_REFL] THEN MATCH_MP_TAC CARD_EQ_IMAGE THEN
  SIMP_TAC[VECTOR_ARITH `a + x:real^N = a + y <=> x = y`]) in
add_translation_invariants card_translation_invariants;;

let card_linear_invariants = (CONJUNCTS o prove)
 (`(!(f:real^M->real^N) s (t:A->bool).
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (IMAGE f s =_c t <=> s =_c t)) /\
   (!(f:real^M->real^N) (s:A->bool) t.
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (s =_c IMAGE f t <=> s =_c t)) /\
   (!(f:real^M->real^N) s (t:A->bool).
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (IMAGE f s <_c t <=> s <_c t)) /\
   (!(f:real^M->real^N) (s:A->bool) t.
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (s <_c IMAGE f t <=> s <_c t)) /\
   (!(f:real^M->real^N) s (t:A->bool).
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (IMAGE f s <=_c t <=> s <=_c t)) /\
   (!(f:real^M->real^N) (s:A->bool) t.
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (s <=_c IMAGE f t <=> s <=_c t)) /\
   (!(f:real^M->real^N) s (t:A->bool).
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (IMAGE f s >_c t <=> s >_c t)) /\
   (!(f:real^M->real^N) (s:A->bool) t.
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (s >_c IMAGE f t <=> s >_c t)) /\
   (!(f:real^M->real^N) s (t:A->bool).
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (IMAGE f s >=_c t <=> s >=_c t)) /\
   (!(f:real^M->real^N) (s:A->bool) t.
     linear f /\ (!x y. f x = f y ==> x = y)
     ==> (s >=_c IMAGE f t <=> s >=_c t))`,
  REWRITE_TAC[gt_c; ge_c] THEN REPEAT STRIP_TAC THENL
   [MATCH_MP_TAC CARD_EQ_CONG;
    MATCH_MP_TAC CARD_EQ_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LT_CONG;
    MATCH_MP_TAC CARD_LE_CONG;
    MATCH_MP_TAC CARD_LE_CONG] THEN
  REWRITE_TAC[CARD_EQ_REFL] THEN MATCH_MP_TAC CARD_EQ_IMAGE THEN
  ASM_MESON_TAC[]) in
add_linear_invariants card_linear_invariants;;

(* ------------------------------------------------------------------------- *)
(* Basic homeomorphism definitions.                                          *)
(* ------------------------------------------------------------------------- *)


let homeomorphism = new_definition
  `homeomorphism (s,t) (f,g) <=>
     (!x. x IN s ==> (g(f(x)) = x)) /\ (IMAGE f s = t) /\ f continuous_on s /\
     (!y. y IN t ==> (f(g(y)) = y)) /\ (IMAGE g t = s) /\ g continuous_on t`;;

parse_as_infix("homeomorphic",(12,"right"));;


let homeomorphic = new_definition
  `s homeomorphic t <=> ?f g. homeomorphism (s,t) (f,g)`;;


let HOMEOMORPHISM = 
prove
 (`!s:real^M->bool t:real^N->bool f g.
        homeomorphism (s,t) (f,g) <=>
         f continuous_on s /\ IMAGE f s SUBSET t /\
         g continuous_on t /\ IMAGE g t SUBSET s /\
         (!x. x IN s ==> g (f x) = x) /\
         (!y. y IN t ==> f (g y) = y)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphism] THEN
  EQ_TAC THEN SIMP_TAC[] THEN SET_TAC[]);;


let HOMEOMORPHISM_OF_SUBSETS = 
prove
 (`!f g s t s' t'.
    homeomorphism (s,t) (f,g) /\ s' SUBSET s /\ t' SUBSET t /\ IMAGE f s' = t'
    ==> homeomorphism (s',t') (f,g)`,

  REWRITE_TAC[homeomorphism] THEN
  REPEAT STRIP_TAC THEN
  TRY(MATCH_MP_TAC CONTINUOUS_ON_SUBSET) THEN ASM SET_TAC[]);;


let HOMEOMORPHISM_ID = 
prove
 (`!s:real^N->bool. homeomorphism (s,s) ((\x. x),(\x. x))`,

  REWRITE_TAC[homeomorphism; IMAGE_ID; CONTINUOUS_ON_ID]);;


let HOMEOMORPHISM_I = 
prove
 (`!s:real^N->bool. homeomorphism (s,s) (I,I)`,

  REWRITE_TAC[I_DEF; HOMEOMORPHISM_ID]);;


let HOMEOMORPHIC_REFL = 
prove
 (`!s:real^N->bool. s homeomorphic s`,

  REWRITE_TAC[homeomorphic] THEN MESON_TAC[HOMEOMORPHISM_I]);;


let HOMEOMORPHISM_SYM = 
prove
 (`!f:real^M->real^N g s t.
        homeomorphism (s,t) (f,g) <=> homeomorphism (t,s) (g,f)`,

  REWRITE_TAC[homeomorphism] THEN MESON_TAC[]);;


let HOMEOMORPHIC_SYM = 
prove
 (`!s t. s homeomorphic t <=> t homeomorphic s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; homeomorphism] THEN
  GEN_REWRITE_TAC RAND_CONV [SWAP_EXISTS_THM] THEN
  REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN CONV_TAC TAUT);;


let HOMEOMORPHISM_COMPOSE = 
prove
 (`!f:real^M->real^N g h:real^N->real^P k s t u.
        homeomorphism (s,t) (f,g) /\ homeomorphism (t,u) (h,k)
        ==> homeomorphism (s,u) (h o f,g o k)`,

  SIMP_TAC[homeomorphism; CONTINUOUS_ON_COMPOSE; IMAGE_o; o_THM] THEN
  SET_TAC[]);;


let HOMEOMORPHIC_TRANS = 
prove
 (`!s:real^M->bool t:real^N->bool u:real^P->bool.
        s homeomorphic t /\ t homeomorphic u ==> s homeomorphic u`,

  REWRITE_TAC[homeomorphic] THEN MESON_TAC[HOMEOMORPHISM_COMPOSE]);;


let HOMEOMORPHIC_IMP_CARD_EQ = 
prove
 (`!s:real^M->bool t:real^N->bool. s homeomorphic t ==> s =_c t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; homeomorphism; eq_c] THEN
  MATCH_MP_TAC MONO_EXISTS THEN SET_TAC[]);;


let HOMEOMORPHIC_EMPTY = 
prove
 (`(!s. (s:real^N->bool) homeomorphic ({}:real^M->bool) <=> s = {}) /\
   (!s. ({}:real^M->bool) homeomorphic (s:real^N->bool) <=> s = {})`,

  REWRITE_TAC[homeomorphic; homeomorphism; IMAGE_CLAUSES; IMAGE_EQ_EMPTY] THEN
  REPEAT STRIP_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[continuous_on; NOT_IN_EMPTY]);;


let HOMEOMORPHIC_MINIMAL = 
prove
 (`!s t. s homeomorphic t <=>
            ?f g. (!x. x IN s ==> f(x) IN t /\ (g(f(x)) = x)) /\
                  (!y. y IN t ==> g(y) IN s /\ (f(g(y)) = y)) /\
                  f continuous_on s /\ g continuous_on t`,

  REWRITE_TAC[homeomorphic; homeomorphism; EXTENSION; IN_IMAGE] THEN
  REPEAT GEN_TAC THEN REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN MESON_TAC[]);;


let HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_SELF = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> (IMAGE f s) homeomorphic s`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INJECTIVE_LEFT_INVERSE]) THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN DISCH_TAC THEN
  EXISTS_TAC `f:real^M->real^N` THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_ON; FORALL_IN_IMAGE; FUN_IN_IMAGE] THEN
  ASM_SIMP_TAC[continuous_on; IMP_CONJ; FORALL_IN_IMAGE] THEN
  X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  MP_TAC(ISPEC `f:real^M->real^N` LINEAR_INJECTIVE_BOUNDED_BELOW_POS) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `e * B:real` THEN ASM_SIMP_TAC[REAL_LT_MUL] THEN
  X_GEN_TAC `y:real^M` THEN ASM_SIMP_TAC[dist; GSYM LINEAR_SUB] THEN
  DISCH_TAC THEN ASM_SIMP_TAC[GSYM REAL_LT_LDIV_EQ] THEN
  MATCH_MP_TAC(REAL_ARITH `a <= b ==> b < x ==> a < x`) THEN
  ASM_SIMP_TAC[REAL_LE_RDIV_EQ]);;


let HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_LEFT_EQ = 
prove
 (`!f:real^M->real^N s t.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> ((IMAGE f s) homeomorphic t <=> s homeomorphic t)`,

  REPEAT GEN_TAC THEN DISCH_THEN(ASSUME_TAC o SPEC `s:real^M->bool` o
    MATCH_MP HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_SELF) THEN
  EQ_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [HOMEOMORPHIC_SYM]);
    POP_ASSUM MP_TAC] THEN
  REWRITE_TAC[IMP_IMP; HOMEOMORPHIC_TRANS]);;


let HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_RIGHT_EQ = 
prove
 (`!f:real^M->real^N s t.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> (s homeomorphic (IMAGE f t) <=> s homeomorphic t)`,

  ONCE_REWRITE_TAC[HOMEOMORPHIC_SYM] THEN
  REWRITE_TAC[HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_LEFT_EQ]);;

add_linear_invariants
  [HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_LEFT_EQ;
   HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_RIGHT_EQ];;


let HOMEOMORPHIC_TRANSLATION_SELF = 
prove
 (`!a:real^N s. (IMAGE (\x. a + x) s) homeomorphic s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  EXISTS_TAC `\x:real^N. x - a` THEN
  EXISTS_TAC `\x:real^N. a + x` THEN
  SIMP_TAC[FORALL_IN_IMAGE; CONTINUOUS_ON_SUB; CONTINUOUS_ON_ID;
           CONTINUOUS_ON_CONST; CONTINUOUS_ON_ADD; VECTOR_ADD_SUB] THEN
  REWRITE_TAC[IN_IMAGE] THEN MESON_TAC[]);;


let HOMEOMORPHIC_TRANSLATION_LEFT_EQ = 
prove
 (`!a:real^N s t.
      (IMAGE (\x. a + x) s) homeomorphic t <=> s homeomorphic t`,


let HOMEOMORPHIC_TRANSLATION_RIGHT_EQ = 
prove
 (`!a:real^N s t.
      s homeomorphic (IMAGE (\x. a + x) t) <=> s homeomorphic t`,

  ONCE_REWRITE_TAC[HOMEOMORPHIC_SYM] THEN
  REWRITE_TAC[HOMEOMORPHIC_TRANSLATION_LEFT_EQ]);;

add_translation_invariants
  [HOMEOMORPHIC_TRANSLATION_LEFT_EQ;
   HOMEOMORPHIC_TRANSLATION_RIGHT_EQ];;


let HOMEOMORPHISM_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N g s t.
    homeomorphism (s,t) (f,g)
    ==> !u. u SUBSET t
            ==> (open_in (subtopology euclidean s) {x | x IN s /\ f x IN u} <=>
                 open_in (subtopology euclidean t) u)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphism] THEN
  STRIP_TAC THEN MATCH_MP_TAC CONTINUOUS_RIGHT_INVERSE_IMP_QUOTIENT_MAP THEN
  EXISTS_TAC `g:real^N->real^M` THEN ASM_REWRITE_TAC[SUBSET_REFL]);;


let HOMEOMORPHIC_PCROSS = 
prove
 (`!s:real^M->bool t:real^N->bool s':real^P->bool t':real^Q->bool.
        s homeomorphic s' /\ t homeomorphic t'
        ==> (s PCROSS t) homeomorphic (s' PCROSS t')`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE] THEN
  DISCH_THEN(CONJUNCTS_THEN2
   (X_CHOOSE_THEN `f:real^M->real^P`
     (X_CHOOSE_THEN `f':real^P->real^M` STRIP_ASSUME_TAC))
   (X_CHOOSE_THEN `g:real^N->real^Q`
     (X_CHOOSE_THEN `g':real^Q->real^N` STRIP_ASSUME_TAC))) THEN
  MAP_EVERY EXISTS_TAC
   [`(\z. pastecart (f(fstcart z)) (g(sndcart z)))
     :real^(M,N)finite_sum->real^(P,Q)finite_sum`;
    `(\z. pastecart (f'(fstcart z)) (g'(sndcart z)))
     :real^(P,Q)finite_sum->real^(M,N)finite_sum`] THEN
  ASM_SIMP_TAC[FORALL_IN_PCROSS; FSTCART_PASTECART; SNDCART_PASTECART;
               SUBSET; FORALL_IN_IMAGE; PASTECART_IN_PCROSS] THEN
  CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_ON_PASTECART THEN
  CONJ_TAC THEN ONCE_REWRITE_TAC[GSYM o_DEF] THEN
  MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
  SIMP_TAC[LINEAR_FSTCART; LINEAR_SNDCART; LINEAR_CONTINUOUS_ON] THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
          CONTINUOUS_ON_SUBSET)) THEN
  REWRITE_TAC[FORALL_IN_IMAGE; FORALL_IN_PCROSS; SUBSET] THEN
  SIMP_TAC[FSTCART_PASTECART; SNDCART_PASTECART]);;


let HOMEOMORPHIC_PCROSS_SYM = 
prove
 (`!s:real^M->bool t:real^N->bool. (s PCROSS t) homeomorphic (t PCROSS s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; homeomorphism] THEN
  EXISTS_TAC `(\z. pastecart (sndcart z) (fstcart z))
              :real^(M,N)finite_sum->real^(N,M)finite_sum` THEN
  EXISTS_TAC `(\z. pastecart (sndcart z) (fstcart z))
              :real^(N,M)finite_sum->real^(M,N)finite_sum` THEN
  REWRITE_TAC[GSYM SUBSET_ANTISYM_EQ; SUBSET; FORALL_IN_IMAGE] THEN
  SIMP_TAC[CONTINUOUS_ON_PASTECART; LINEAR_CONTINUOUS_ON;
           LINEAR_FSTCART; LINEAR_SNDCART] THEN
  REWRITE_TAC[FORALL_IN_PCROSS; FSTCART_PASTECART; SNDCART_PASTECART;
    IN_IMAGE; EXISTS_PASTECART; PASTECART_INJ; PASTECART_IN_PCROSS] THEN
  MESON_TAC[]);;


let HOMEOMORPHIC_PCROSS_ASSOC = 
prove
 (`!s:real^M->bool t:real^N->bool u:real^P->bool.
        (s PCROSS (t PCROSS u)) homeomorphic ((s PCROSS t) PCROSS u)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
  MAP_EVERY EXISTS_TAC
   [`\z:real^(M,(N,P)finite_sum)finite_sum.
        pastecart (pastecart (fstcart z) (fstcart(sndcart z)))
                  (sndcart(sndcart z))`;
    `\z:real^((M,N)finite_sum,P)finite_sum.
        pastecart (fstcart(fstcart z))
                  (pastecart (sndcart(fstcart z)) (sndcart z))`] THEN
  REWRITE_TAC[FORALL_IN_PCROSS; SUBSET; FORALL_IN_IMAGE;
              RIGHT_FORALL_IMP_THM; IMP_CONJ] THEN
  SIMP_TAC[FSTCART_PASTECART; SNDCART_PASTECART; PASTECART_IN_PCROSS] THEN
  CONJ_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_ON THEN
  REPEAT(MATCH_MP_TAC LINEAR_PASTECART THEN CONJ_TAC) THEN
  TRY(GEN_REWRITE_TAC RAND_CONV [GSYM o_DEF] THEN
      MATCH_MP_TAC LINEAR_COMPOSE) THEN
  REWRITE_TAC[LINEAR_FSTCART; LINEAR_SNDCART]);;


let HOMEOMORPHIC_SCALING_LEFT = 
prove
 (`!c. &0 < c
       ==> !s t. (IMAGE (\x. c % x) s) homeomorphic t <=> s homeomorphic t`,

  REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN REPEAT GEN_TAC THEN DISCH_TAC THEN
  MATCH_MP_TAC HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_LEFT_EQ THEN
  ASM_SIMP_TAC[VECTOR_MUL_LCANCEL; REAL_LT_IMP_NZ; LINEAR_SCALING]);;


let HOMEOMORPHIC_SCALING_RIGHT = 
prove
 (`!c. &0 < c
       ==> !s t. s homeomorphic (IMAGE (\x. c % x) t) <=> s homeomorphic t`,

  REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN REPEAT GEN_TAC THEN DISCH_TAC THEN
  MATCH_MP_TAC HOMEOMORPHIC_INJECTIVE_LINEAR_IMAGE_RIGHT_EQ THEN
  ASM_SIMP_TAC[VECTOR_MUL_LCANCEL; REAL_LT_IMP_NZ; LINEAR_SCALING]);;


let HOMEOMORPHIC_SUBSPACES = 
prove
 (`!s:real^M->bool t:real^N->bool.
        subspace s /\ subspace t /\ dim s = dim t ==> s homeomorphic t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
  DISCH_THEN(MP_TAC o MATCH_MP ISOMETRIES_SUBSPACES) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `f:real^M->real^N` THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^N->real^M` THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_INTER; IN_CBALL_0] THEN
  SIMP_TAC[LINEAR_CONTINUOUS_ON] THEN ASM SET_TAC[]);;


let HOMEOMORPHIC_FINITE = 
prove
 (`!s:real^M->bool t:real^N->bool.
        FINITE s /\ FINITE t ==> (s homeomorphic t <=> CARD s = CARD t)`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [DISCH_THEN(MP_TAC o MATCH_MP HOMEOMORPHIC_IMP_CARD_EQ) THEN
    ASM_SIMP_TAC[CARD_EQ_CARD];
    STRIP_TAC THEN REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
    MP_TAC(ISPECL [`s:real^M->bool`; `t:real^N->bool`]
        CARD_EQ_BIJECTIONS) THEN
    ASM_REWRITE_TAC[] THEN
    REPEAT(MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC) THEN
    ASM_SIMP_TAC[CONTINUOUS_ON_FINITE] THEN ASM SET_TAC[]]);;


let HOMEOMORPHIC_FINITE_STRONG = 
prove
 (`!s:real^M->bool t:real^N->bool.
        FINITE s \/ FINITE t
        ==> (s homeomorphic t <=> FINITE s /\ FINITE t /\ CARD s = CARD t)`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN EQ_TAC THEN
  SIMP_TAC[HOMEOMORPHIC_FINITE] THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CARD_FINITE_CONG o MATCH_MP
    HOMEOMORPHIC_IMP_CARD_EQ) THEN
  FIRST_X_ASSUM DISJ_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[HOMEOMORPHIC_FINITE]);;


let HOMEOMORPHIC_SING = 
prove
 (`!a:real^M b:real^N. {a} homeomorphic {b}`,


let HOMEOMORPHIC_PCROSS_SING = 
prove
 (`(!s:real^M->bool a:real^N. s homeomorphic (s PCROSS {a})) /\
   (!s:real^M->bool a:real^N. s homeomorphic ({a} PCROSS s))`,

  MATCH_MP_TAC(TAUT `(p ==> q) /\ p ==> p /\ q`) THEN CONJ_TAC THENL
   [MESON_TAC[HOMEOMORPHIC_PCROSS_SYM; HOMEOMORPHIC_TRANS]; ALL_TAC] THEN
  REPEAT GEN_TAC THEN REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
  EXISTS_TAC `\x. (pastecart x a:real^(M,N)finite_sum)` THEN
  EXISTS_TAC `fstcart:real^(M,N)finite_sum->real^M` THEN
  SIMP_TAC[CONTINUOUS_ON_PASTECART; CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID] THEN
  SIMP_TAC[LINEAR_FSTCART; LINEAR_CONTINUOUS_ON; SUBSET; FORALL_IN_IMAGE] THEN
  REWRITE_TAC[FORALL_IN_PCROSS; PASTECART_IN_PCROSS; IN_SING] THEN
  SIMP_TAC[FSTCART_PASTECART]);;

(* ------------------------------------------------------------------------- *)
(* Inverse function property for open/closed maps.                           *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_ON_INVERSE_OPEN_MAP = 
prove
 (`!f:real^M->real^N g s t.
        f continuous_on s /\ IMAGE f s = t /\ (!x. x IN s ==> g(f x) = x) /\
        (!u. open_in (subtopology euclidean s) u
             ==> open_in (subtopology euclidean t) (IMAGE f u))
        ==> g continuous_on t`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`g:real^N->real^M`; `t:real^N->bool`; `s:real^M->bool`]
        CONTINUOUS_ON_OPEN_GEN) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; DISCH_THEN SUBST1_TAC] THEN
  X_GEN_TAC `u:real^M->bool` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `u:real^M->bool`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  FIRST_ASSUM(MP_TAC o CONJUNCT1 o GEN_REWRITE_RULE I [open_in]) THEN
  ASM SET_TAC[]);;


let CONTINUOUS_ON_INVERSE_CLOSED_MAP = 
prove
 (`!f:real^M->real^N g s t.
        f continuous_on s /\ IMAGE f s = t /\ (!x. x IN s ==> g(f x) = x) /\
        (!u. closed_in (subtopology euclidean s) u
             ==> closed_in (subtopology euclidean t) (IMAGE f u))
        ==> g continuous_on t`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`g:real^N->real^M`; `t:real^N->bool`; `s:real^M->bool`]
        CONTINUOUS_ON_CLOSED_GEN) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; DISCH_THEN SUBST1_TAC] THEN
  X_GEN_TAC `u:real^M->bool` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `u:real^M->bool`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
  FIRST_ASSUM(MP_TAC o CONJUNCT1 o GEN_REWRITE_RULE I [closed_in]) THEN
  REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN ASM SET_TAC[]);;


let HOMEOMORPHISM_INJECTIVE_OPEN_MAP = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y) /\
        (!u. open_in (subtopology euclidean s) u
             ==> open_in (subtopology euclidean t) (IMAGE f u))
        ==> ?g. homeomorphism (s,t) (f,g)`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INJECTIVE_ON_LEFT_INVERSE]) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^N->real^M` THEN
  DISCH_TAC THEN ASM_SIMP_TAC[homeomorphism] THEN
  REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  MATCH_MP_TAC CONTINUOUS_ON_INVERSE_OPEN_MAP THEN ASM_MESON_TAC[]);;


let HOMEOMORPHISM_INJECTIVE_CLOSED_MAP = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y) /\
        (!u. closed_in (subtopology euclidean s) u
             ==> closed_in (subtopology euclidean t) (IMAGE f u))
        ==> ?g. homeomorphism (s,t) (f,g)`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INJECTIVE_ON_LEFT_INVERSE]) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `g:real^N->real^M` THEN
  DISCH_TAC THEN ASM_SIMP_TAC[homeomorphism] THEN
  REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  MATCH_MP_TAC CONTINUOUS_ON_INVERSE_CLOSED_MAP THEN ASM_MESON_TAC[]);;


let HOMEOMORPHISM_IMP_OPEN_MAP = 
prove
 (`!f:real^M->real^N g s t u.
        homeomorphism (s,t) (f,g) /\ open_in (subtopology euclidean s) u
        ==> open_in (subtopology euclidean t) (IMAGE f u)`,

  REWRITE_TAC[homeomorphism] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^M->real^N) u =
                 {y | y IN t /\ g(y) IN u}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o CONJUNCT1 o GEN_REWRITE_RULE I [open_in]) THEN
    ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_ON_IMP_OPEN_IN THEN ASM_REWRITE_TAC[]]);;


let HOMEOMORPHISM_IMP_CLOSED_MAP = 
prove
 (`!f:real^M->real^N g s t u.
        homeomorphism (s,t) (f,g) /\ closed_in (subtopology euclidean s) u
        ==> closed_in (subtopology euclidean t) (IMAGE f u)`,

  REWRITE_TAC[homeomorphism] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^M->real^N) u =
                 {y | y IN t /\ g(y) IN u}`
  SUBST1_TAC THENL
   [FIRST_ASSUM(MP_TAC o CONJUNCT1 o GEN_REWRITE_RULE I [closed_in]) THEN
    REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN ASM SET_TAC[];
    MATCH_MP_TAC CONTINUOUS_ON_IMP_CLOSED_IN THEN ASM_REWRITE_TAC[]]);;


let HOMEOMORPHISM_INJECTIVE_OPEN_MAP_EQ = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y)
        ==> ((?g. homeomorphism (s,t) (f,g)) <=>
             !u. open_in (subtopology euclidean s) u
                 ==> open_in (subtopology euclidean t) (IMAGE f u))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN REPEAT STRIP_TAC THENL
   [MATCH_MP_TAC HOMEOMORPHISM_IMP_OPEN_MAP THEN ASM_MESON_TAC[];
    MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_OPEN_MAP THEN
    ASM_REWRITE_TAC[]]);;


let HOMEOMORPHISM_INJECTIVE_CLOSED_MAP_EQ = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y)
        ==> ((?g. homeomorphism (s,t) (f,g)) <=>
             !u. closed_in (subtopology euclidean s) u
                 ==> closed_in (subtopology euclidean t) (IMAGE f u))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN REPEAT STRIP_TAC THENL
   [MATCH_MP_TAC HOMEOMORPHISM_IMP_CLOSED_MAP THEN ASM_MESON_TAC[];
    MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_CLOSED_MAP THEN
    ASM_REWRITE_TAC[]]);;


let INJECTIVE_MAP_OPEN_IFF_CLOSED = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\
        (!x y. x IN s /\ y IN s /\ f x = f y ==> x = y)
        ==> ((!u. open_in (subtopology euclidean s) u
                  ==> open_in (subtopology euclidean t) (IMAGE f u)) <=>
             (!u. closed_in (subtopology euclidean s) u
                  ==> closed_in (subtopology euclidean t) (IMAGE f u)))`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC EQ_TRANS THEN
  EXISTS_TAC `?g:real^N->real^M. homeomorphism (s,t) (f,g)` THEN
  CONJ_TAC THENL
   [CONV_TAC SYM_CONV THEN MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_OPEN_MAP_EQ;
    MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_CLOSED_MAP_EQ] THEN
  ASM_REWRITE_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Relatively weak hypotheses if the domain of the function is compact.      *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_IMP_CLOSED_MAP = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\ compact s
        ==> !u. closed_in (subtopology euclidean s) u
                ==> closed_in (subtopology euclidean t) (IMAGE f u)`,

  SIMP_TAC[CLOSED_IN_CLOSED_EQ; COMPACT_IMP_CLOSED] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSED_SUBSET THEN
  EXPAND_TAC "t" THEN ASM_SIMP_TAC[IMAGE_SUBSET] THEN
  MATCH_MP_TAC COMPACT_IMP_CLOSED THEN
  MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN ASM_REWRITE_TAC[] THEN
  ASM_MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_IN_CLOSED_TRANS;
                BOUNDED_SUBSET; CONTINUOUS_ON_SUBSET]);;


let CONTINUOUS_IMP_QUOTIENT_MAP = 
prove
 (`!f:real^M->real^N s t.
        f continuous_on s /\ IMAGE f s = t /\ compact s
        ==> !u. u SUBSET t
                ==> (open_in (subtopology euclidean s)
                             {x | x IN s /\ f x IN u} <=>
                     open_in (subtopology euclidean t) u)`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN FIRST_X_ASSUM(SUBST_ALL_TAC o SYM) THEN
  MATCH_MP_TAC CLOSED_MAP_IMP_QUOTIENT_MAP THEN
  ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC CONTINUOUS_IMP_CLOSED_MAP THEN
  ASM_REWRITE_TAC[]);;


let CONTINUOUS_ON_INVERSE = 
prove
 (`!f:real^M->real^N g s.
        f continuous_on s /\ compact s /\ (!x. x IN s ==> (g(f(x)) = x))
        ==> g continuous_on (IMAGE f s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CONTINUOUS_ON_CLOSED] THEN
  SUBGOAL_THEN `IMAGE g (IMAGE (f:real^M->real^N) s) = s` SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_IMAGE] THEN ASM_MESON_TAC[]; ALL_TAC] THEN
  X_GEN_TAC `t:real^M->bool` THEN DISCH_TAC THEN
  REWRITE_TAC[CLOSED_IN_CLOSED] THEN
  EXISTS_TAC `IMAGE (f:real^M->real^N) t` THEN CONJ_TAC THENL
   [MATCH_MP_TAC COMPACT_IMP_CLOSED THEN
    MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_SUBSET) THEN
    REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
    ASM_MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_IN_CLOSED_TRANS;
                  BOUNDED_SUBSET; CONTINUOUS_ON_SUBSET];
    REWRITE_TAC[EXTENSION; IN_INTER; IN_ELIM_THM; IN_IMAGE] THEN
    ASM_MESON_TAC[CLOSED_IN_SUBSET; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY; SUBSET]]);;


let HOMEOMORPHISM_COMPACT = 
prove
 (`!s f t. compact s /\ f continuous_on s /\ (IMAGE f s = t) /\
           (!x y. x IN s /\ y IN s /\ (f x = f y) ==> (x = y))
           ==> ?g. homeomorphism(s,t) (f,g)`,

  REWRITE_TAC[INJECTIVE_ON_LEFT_INVERSE] THEN REPEAT GEN_TAC THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  MATCH_MP_TAC MONO_EXISTS THEN ASM_SIMP_TAC[EXTENSION; homeomorphism] THEN
  FIRST_X_ASSUM(SUBST_ALL_TAC o SYM) THEN
  ASM_MESON_TAC[CONTINUOUS_ON_INVERSE; IN_IMAGE]);;


let HOMEOMORPHIC_COMPACT = 
prove
 (`!s f t. compact s /\ f continuous_on s /\ (IMAGE f s = t) /\
           (!x y. x IN s /\ y IN s /\ (f x = f y) ==> (x = y))
           ==> s homeomorphic t`,

  REWRITE_TAC[homeomorphic] THEN MESON_TAC[HOMEOMORPHISM_COMPACT]);;

(* ------------------------------------------------------------------------- *)
(* Lemmas about composition of homeomorphisms.                               *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHISM_FROM_COMPOSITION_SURJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s = t /\
        g continuous_on t /\ IMAGE g t SUBSET u /\
        (?h. homeomorphism (s,u) (g o f,h))
        ==> (?f'. homeomorphism (s,t) (f,f')) /\
            (?g'. homeomorphism (t,u) (g,g'))`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  RULE_ASSUM_TAC(REWRITE_RULE[homeomorphism; o_THM]) THEN
  MATCH_MP_TAC(TAUT `q /\ (q ==> p) ==> p /\ q`) THEN CONJ_TAC THENL
   [MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_OPEN_MAP THEN
    REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
    MATCH_MP_TAC OPEN_MAP_FROM_COMPOSITION_SURJECTIVE THEN
    MAP_EVERY EXISTS_TAC [`f:real^M->real^N`; `s:real^M->bool`] THEN
    ASM_REWRITE_TAC[] THEN REPEAT STRIP_TAC THEN
    MATCH_MP_TAC HOMEOMORPHISM_IMP_OPEN_MAP THEN
    MAP_EVERY EXISTS_TAC [`h:real^P->real^M`; `s:real^M->bool`] THEN
    ASM_REWRITE_TAC[homeomorphism; o_THM];
    REWRITE_TAC[homeomorphism; o_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `g':real^P->real^N` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `(h:real^P->real^M) o (g:real^N->real^P)` THEN
    ASM_SIMP_TAC[o_THM; IMAGE_o] THEN
    CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
    ASM_MESON_TAC[CONTINUOUS_ON_SUBSET]]);;


let HOMEOMORPHISM_FROM_COMPOSITION_INJECTIVE = 
prove
 (`!f:real^M->real^N g:real^N->real^P s t u.
        f continuous_on s /\ IMAGE f s SUBSET t /\
        g continuous_on t /\ IMAGE g t SUBSET u /\
        (!x y. x IN t /\ y IN t /\ g x = g y ==> x = y) /\
        (?h. homeomorphism (s,u) (g o f,h))
        ==> (?f'. homeomorphism (s,t) (f,f')) /\
            (?g'. homeomorphism (t,u) (g,g'))`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  RULE_ASSUM_TAC(REWRITE_RULE[homeomorphism; o_THM]) THEN
  MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
   [MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_OPEN_MAP THEN
    REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
    MATCH_MP_TAC OPEN_MAP_FROM_COMPOSITION_INJECTIVE THEN
    MAP_EVERY EXISTS_TAC [`g:real^N->real^P`; `u:real^P->bool`] THEN
    ASM_REWRITE_TAC[] THEN REPEAT STRIP_TAC THEN
    MATCH_MP_TAC HOMEOMORPHISM_IMP_OPEN_MAP THEN
    MAP_EVERY EXISTS_TAC [`h:real^P->real^M`; `s:real^M->bool`] THEN
    ASM_REWRITE_TAC[homeomorphism; o_THM];
    REWRITE_TAC[homeomorphism; o_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `f':real^N->real^M` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `(f:real^M->real^N) o (h:real^P->real^M)` THEN
    ASM_SIMP_TAC[o_THM; IMAGE_o] THEN
    REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
    MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
    ASM_MESON_TAC[CONTINUOUS_ON_SUBSET]]);;

(* ------------------------------------------------------------------------- *)
(* Preservation of topological properties.                                   *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHIC_COMPACTNESS = 
prove
 (`!s t. s homeomorphic t ==> (compact s <=> compact t)`,

  REWRITE_TAC[homeomorphic; homeomorphism] THEN
  MESON_TAC[COMPACT_CONTINUOUS_IMAGE]);;


let HOMEOMORPHIC_CONNECTEDNESS = 
prove
 (`!s t. s homeomorphic t ==> (connected s <=> connected t)`,

  REWRITE_TAC[homeomorphic; homeomorphism] THEN
  MESON_TAC[CONNECTED_CONTINUOUS_IMAGE]);;

(* ------------------------------------------------------------------------- *)
(* Results on translation, scaling etc.                                      *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHIC_SCALING = 
prove
 (`!s:real^N->bool c. ~(c = &0) ==> s homeomorphic (IMAGE (\x. c % x) s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  MAP_EVERY EXISTS_TAC [`\x:real^N. c % x`; `\x:real^N. inv(c) % x`] THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_CMUL; CONTINUOUS_ON_ID; FORALL_IN_IMAGE] THEN
  ASM_SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; REAL_MUL_RINV] THEN
  SIMP_TAC[VECTOR_MUL_LID; IN_IMAGE; REAL_MUL_LID] THEN MESON_TAC[]);;


let HOMEOMORPHIC_TRANSLATION = 
prove
 (`!s a:real^N. s homeomorphic (IMAGE (\x. a + x) s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  MAP_EVERY EXISTS_TAC [`\x:real^N. a +  x`; `\x:real^N. --a + x`] THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_ADD; CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID] THEN
  SIMP_TAC[VECTOR_ADD_ASSOC; VECTOR_ADD_LINV; VECTOR_ADD_RINV;
           FORALL_IN_IMAGE; VECTOR_ADD_LID] THEN
  REWRITE_TAC[IN_IMAGE] THEN MESON_TAC[]);;


let HOMEOMORPHIC_AFFINITY = 
prove
 (`!s a:real^N c. ~(c = &0) ==> s homeomorphic (IMAGE (\x. a + c % x) s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC HOMEOMORPHIC_TRANS THEN
  EXISTS_TAC `IMAGE (\x:real^N. c % x) s` THEN
  ASM_SIMP_TAC[HOMEOMORPHIC_SCALING] THEN
  SUBGOAL_THEN `(\x:real^N. a + c % x) = (\x. a + x) o (\x. c % x)`
  SUBST1_TAC THENL [REWRITE_TAC[o_DEF]; ALL_TAC] THEN
  REWRITE_TAC[IMAGE_o; HOMEOMORPHIC_TRANSLATION]);;

let [HOMEOMORPHIC_BALLS; HOMEOMORPHIC_CBALLS; HOMEOMORPHIC_SPHERES] =
  (CONJUNCTS o prove)
 (`(!a:real^N b:real^N d e.
      &0 < d /\ &0 < e ==> ball(a,d) homeomorphic ball(b,e)) /\
   (!a:real^N b:real^N d e.
      &0 < d /\ &0 < e ==> cball(a,d) homeomorphic cball(b,e)) /\
   (!a:real^N b:real^N d e.
      &0 < d /\ &0 < e ==> sphere(a,d) homeomorphic sphere(b,e))`,
  REPEAT STRIP_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  EXISTS_TAC `\x:real^N. b + (e / d) % (x - a)` THEN
  EXISTS_TAC `\x:real^N. a + (d / e) % (x - b)` THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_ADD; CONTINUOUS_ON_SUB; CONTINUOUS_ON_CMUL;
    CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID; IN_BALL; IN_CBALL; IN_SPHERE] THEN
  REWRITE_TAC[dist; VECTOR_ARITH `a - (a + b) = --b:real^N`; NORM_NEG] THEN
  REWRITE_TAC[real_div; VECTOR_ARITH
   `a + d % ((b + e % (x - a)) - b) = (&1 - d * e) % a + (d * e) % x`] THEN
  ONCE_REWRITE_TAC[REAL_ARITH
    `(e * d') * (d * e') = (d * d') * (e * e')`] THEN
  ASM_SIMP_TAC[REAL_MUL_RINV; REAL_LT_IMP_NZ; REAL_MUL_LID; REAL_SUB_REFL] THEN
  REWRITE_TAC[NORM_MUL; VECTOR_MUL_LZERO; VECTOR_MUL_LID; VECTOR_ADD_LID] THEN
  ASM_SIMP_TAC[REAL_ABS_MUL; REAL_ABS_INV; REAL_ARITH
   `&0 < x ==> (abs x = x)`] THEN
  GEN_REWRITE_TAC(BINOP_CONV o BINDER_CONV o funpow 2 RAND_CONV)
        [GSYM REAL_MUL_RID] THEN
  ONCE_REWRITE_TAC[AC REAL_MUL_AC `(a * b) * c = (a * c) * b`] THEN
  ASM_SIMP_TAC[REAL_LE_LMUL_EQ; GSYM real_div; REAL_LE_LDIV_EQ; REAL_MUL_LID;
    GSYM REAL_MUL_ASSOC; REAL_LT_LMUL_EQ; REAL_LT_LDIV_EQ; NORM_SUB] THEN
  ASM_SIMP_TAC[REAL_DIV_REFL; REAL_LT_IMP_NZ; REAL_MUL_RID]);;

(* ------------------------------------------------------------------------- *)
(* Homeomorphism of one-point compactifications.                             *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHIC_ONE_POINT_COMPACTIFICATIONS = 
prove
 (`!s:real^M->bool t:real^N->bool a b.
        compact s /\ compact t /\ a IN s /\ b IN t /\
        (s DELETE a) homeomorphic (t DELETE b)
        ==> s homeomorphic t`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC HOMEOMORPHIC_COMPACT THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [homeomorphic]) THEN
  REWRITE_TAC[HOMEOMORPHISM; LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`f:real^M->real^N`; `g:real^N->real^M`] THEN
  STRIP_TAC THEN
  EXISTS_TAC `\x. if x = a then b else (f:real^M->real^N) x` THEN
  ASM_REWRITE_TAC[] THEN CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
  REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
  ASM_CASES_TAC `x:real^M = a` THEN ASM_REWRITE_TAC[] THENL
   [REWRITE_TAC[continuous_within] THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    MP_TAC(ISPECL [`b:real^N`; `e:real`] CENTRE_IN_BALL) THEN
    ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
    SUBGOAL_THEN
      `closed_in (subtopology euclidean s)
                 { x | x IN (s DELETE a) /\
                       (f:real^M->real^N)(x) IN t DIFF ball(b,e)}`
    MP_TAC THENL
     [MATCH_MP_TAC CLOSED_SUBSET THEN CONJ_TAC THENL [SET_TAC[]; ALL_TAC] THEN
      MATCH_MP_TAC COMPACT_IMP_CLOSED THEN SUBGOAL_THEN
       `{x | x IN s DELETE a /\ f x IN t DIFF ball(b,e)} =
        IMAGE (g:real^N->real^M) (t DIFF ball (b,e))`
      SUBST1_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
      ASM_SIMP_TAC[COMPACT_DIFF; OPEN_BALL] THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ]
        CONTINUOUS_ON_SUBSET)) THEN ASM SET_TAC[];
      REWRITE_TAC[closed_in; open_in; TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN
      DISCH_THEN(MP_TAC o SPEC `a:real^M` o last o CONJUNCTS) THEN
      ASM_REWRITE_TAC[IN_ELIM_THM; IN_DIFF; IN_DELETE] THEN
      SIMP_TAC[IMP_CONJ; DE_MORGAN_THM] THEN
      MATCH_MP_TAC MONO_EXISTS THEN REPEAT STRIP_TAC THEN
      ASM_REWRITE_TAC[] THEN COND_CASES_TAC THEN
      ASM_REWRITE_TAC[DIST_REFL] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
      RULE_ASSUM_TAC(REWRITE_RULE[IN_BALL]) THEN ASM SET_TAC[]];
    UNDISCH_TAC `(f:real^M->real^N) continuous_on (s DELETE a)` THEN
    REWRITE_TAC[CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^M`) THEN ASM_REWRITE_TAC[IN_DELETE] THEN
    REWRITE_TAC[continuous_within] THEN
    MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
    ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[IN_DELETE] THEN
    DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `min d (dist(a:real^M,x))` THEN
    ASM_REWRITE_TAC[REAL_LT_MIN; GSYM DIST_NZ] THEN
    ASM_MESON_TAC[REAL_LT_REFL]]);;

(* ------------------------------------------------------------------------- *)
(* Homeomorphisms between open intervals in real^1 and then in real^N.       *)
(* Could prove similar things for closed intervals, but they drop out of     *)
(* later stuff in "convex.ml" even more easily.                              *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHIC_OPEN_INTERVALS_1 = 
prove
 (`!a b c d.
        drop a < drop b /\ drop c < drop d
        ==> interval(a,b) homeomorphic interval(c,d)`,

  SUBGOAL_THEN
   `!a b. drop a < drop b
          ==> interval(vec 0:real^1,vec 1) homeomorphic interval(a,b)`
  ASSUME_TAC THENL
   [REPEAT STRIP_TAC THEN REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
    EXISTS_TAC `(\x. a + drop x % (b - a)):real^1->real^1` THEN
    EXISTS_TAC `(\x. inv(drop b - drop a) % (x - a)):real^1->real^1` THEN
    ASM_REWRITE_TAC[IN_INTERVAL_1; GSYM DROP_EQ] THEN
    REWRITE_TAC[DROP_ADD; DROP_CMUL; DROP_NEG; DROP_VEC; DROP_SUB] THEN
    REWRITE_TAC[REAL_ARITH `inv b * a:real = a / b`] THEN
    ASM_SIMP_TAC[REAL_LT_LDIV_EQ; REAL_LT_RDIV_EQ; REAL_SUB_LT;
       REAL_LT_ADDR; REAL_EQ_LDIV_EQ; REAL_DIV_RMUL; REAL_LT_IMP_NZ;
       REAL_LT_MUL; REAL_MUL_LZERO; REAL_ADD_SUB; REAL_LT_RMUL_EQ;
       REAL_ARITH `a + x < b <=> x < &1 * (b - a)`] THEN
    REPEAT CONJ_TAC THENL
     [REAL_ARITH_TAC;
      MATCH_MP_TAC CONTINUOUS_ON_ADD THEN REWRITE_TAC[CONTINUOUS_ON_CONST] THEN
      MATCH_MP_TAC CONTINUOUS_ON_VMUL THEN
      REWRITE_TAC[o_DEF; LIFT_DROP; CONTINUOUS_ON_ID];
      MATCH_MP_TAC CONTINUOUS_ON_CMUL THEN
      ASM_SIMP_TAC[CONTINUOUS_ON_SUB; CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID]];
    REPEAT STRIP_TAC THEN
    FIRST_ASSUM(MP_TAC o SPECL [`a:real^1`; `b:real^1`]) THEN
    FIRST_X_ASSUM(MP_TAC o SPECL [`c:real^1`; `d:real^1`]) THEN
    ASM_REWRITE_TAC[GSYM IMP_CONJ_ALT] THEN
    GEN_REWRITE_TAC (LAND_CONV o LAND_CONV) [HOMEOMORPHIC_SYM] THEN
    REWRITE_TAC[HOMEOMORPHIC_TRANS]]);;


let HOMEOMORPHIC_OPEN_INTERVAL_UNIV_1 = 
prove
 (`!a b. drop a < drop b ==> interval(a,b) homeomorphic (:real^1)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPECL [`a:real^1`; `b:real^1`; `--vec 1:real^1`; `vec 1:real^1`]
        HOMEOMORPHIC_OPEN_INTERVALS_1) THEN
  ASM_REWRITE_TAC[DROP_VEC; DROP_NEG] THEN CONV_TAC REAL_RAT_REDUCE_CONV THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] HOMEOMORPHIC_TRANS) THEN
  POP_ASSUM_LIST(K ALL_TAC) THEN
  REWRITE_TAC[HOMEOMORPHIC_MINIMAL; IN_UNIV] THEN
  EXISTS_TAC `\x:real^1. inv(&1 - norm x) % x` THEN
  EXISTS_TAC `\y. if &0 <= drop y then inv(&1 + drop y) % y
                  else inv(&1 - drop y) % y` THEN
  REWRITE_TAC[] THEN REPEAT CONJ_TAC THENL
   [X_GEN_TAC `x:real^1` THEN REWRITE_TAC[IN_INTERVAL_1] THEN
    REWRITE_TAC[DROP_NEG; DROP_VEC; DROP_CMUL; NORM_REAL; GSYM drop] THEN
    SIMP_TAC[REAL_LE_MUL_EQ; REAL_LT_INV_EQ; REAL_LE_MUL_EQ; REAL_ARITH
     `--a < x /\ x < a ==> &0 < a - abs x`] THEN
    SIMP_TAC[real_abs; VECTOR_MUL_ASSOC] THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN STRIP_TAC THEN
    GEN_REWRITE_TAC RAND_CONV [GSYM VECTOR_MUL_LID] THEN
    AP_THM_TAC THEN AP_TERM_TAC THEN
    REPEAT(POP_ASSUM MP_TAC) THEN CONV_TAC REAL_FIELD;
    X_GEN_TAC `y:real^1` THEN COND_CASES_TAC THEN
    ASM_REWRITE_TAC[IN_INTERVAL_1; DROP_NEG; DROP_VEC; REAL_BOUNDS_LT] THEN
    REWRITE_TAC[DROP_CMUL; REAL_ABS_MUL; REAL_ABS_INV] THEN
    REWRITE_TAC[GSYM(ONCE_REWRITE_RULE[REAL_MUL_SYM] real_div)] THEN
    ASM_SIMP_TAC[REAL_LT_LDIV_EQ; REAL_ARITH `&0 <= x ==> &0 < abs(&1 + x)`;
                 REAL_ARITH `~(&0 <= x) ==> &0 < abs(&1 - x)`] THEN
    (CONJ_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC]) THEN
    REWRITE_TAC[NORM_REAL; VECTOR_MUL_ASSOC] THEN
    REWRITE_TAC[GSYM drop; DROP_CMUL; REAL_ABS_MUL] THEN
    ASM_REWRITE_TAC[real_abs; REAL_LE_INV_EQ] THEN
    ASM_SIMP_TAC[REAL_ARITH `&0 <= x ==> &0 <= &1 + x`;
                 REAL_ARITH `~(&0 <= x) ==> &0 <= &1 - x`] THEN
    GEN_REWRITE_TAC RAND_CONV [GSYM VECTOR_MUL_LID] THEN
    AP_THM_TAC THEN AP_TERM_TAC THEN
    REPEAT(POP_ASSUM MP_TAC) THEN CONV_TAC REAL_FIELD;
    MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
    X_GEN_TAC `x:real^1` THEN
    REWRITE_TAC[IN_INTERVAL_1; DROP_NEG; DROP_VEC] THEN
    DISCH_TAC THEN MATCH_MP_TAC CONTINUOUS_MUL THEN
    REWRITE_TAC[CONTINUOUS_AT_ID] THEN
    ONCE_REWRITE_TAC[GSYM o_DEF] THEN MATCH_MP_TAC CONTINUOUS_INV THEN
    REWRITE_TAC[NETLIMIT_AT; o_DEF; LIFT_SUB; LIFT_DROP] THEN
    CONJ_TAC THENL
     [MATCH_MP_TAC CONTINUOUS_SUB THEN
      SIMP_TAC[CONTINUOUS_CONST; REWRITE_RULE[o_DEF] CONTINUOUS_AT_LIFT_NORM];
      REWRITE_TAC[NORM_REAL; GSYM drop] THEN ASM_REAL_ARITH_TAC];
    SUBGOAL_THEN `(:real^1) = {x | x$1 >= &0} UNION {x | x$1 <= &0}`
    SUBST1_TAC THENL
     [REWRITE_TAC[EXTENSION; IN_UNION; IN_UNION; IN_ELIM_THM; IN_UNIV] THEN
      REAL_ARITH_TAC;
      MATCH_MP_TAC CONTINUOUS_ON_CASES THEN
      REWRITE_TAC[CLOSED_HALFSPACE_COMPONENT_LE; CLOSED_HALFSPACE_COMPONENT_GE;
                  IN_ELIM_THM] THEN
      REWRITE_TAC[GSYM drop; REAL_NOT_LE; real_ge; REAL_LET_ANTISYM] THEN
      SIMP_TAC[REAL_LE_ANTISYM; REAL_SUB_RZERO; REAL_ADD_RID] THEN
      CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_AT_IMP_CONTINUOUS_ON THEN
      X_GEN_TAC `y:real^1` THEN REWRITE_TAC[IN_ELIM_THM; real_ge] THEN
      DISCH_TAC THEN MATCH_MP_TAC CONTINUOUS_MUL THEN
      REWRITE_TAC[CONTINUOUS_AT_ID] THEN
      ONCE_REWRITE_TAC[GSYM o_DEF] THEN MATCH_MP_TAC CONTINUOUS_INV THEN
      REWRITE_TAC[NETLIMIT_AT; o_DEF; LIFT_ADD; LIFT_SUB; LIFT_DROP] THEN
      ASM_SIMP_TAC[CONTINUOUS_ADD; CONTINUOUS_AT_ID; CONTINUOUS_SUB;
                   CONTINUOUS_CONST] THEN
      ASM_REAL_ARITH_TAC]]);;


let HOMEOMORPHIC_OPEN_INTERVALS = 
prove
 (`!a b:real^N c d:real^N.
        (interval(a,b) = {} <=> interval(c,d) = {})
        ==> interval(a,b) homeomorphic interval(c,d)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `interval(c:real^N,d) = {}` THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN ASM_REWRITE_TAC[HOMEOMORPHIC_REFL] THEN
  SUBGOAL_THEN
   `!i. 1 <= i /\ i <= dimindex(:N)
        ==> interval(lift((a:real^N)$i),lift((b:real^N)$i)) homeomorphic
            interval(lift((c:real^N)$i),lift((d:real^N)$i))`
  MP_TAC THENL
   [RULE_ASSUM_TAC(REWRITE_RULE[INTERVAL_NE_EMPTY]) THEN
    ASM_SIMP_TAC[HOMEOMORPHIC_OPEN_INTERVALS_1; LIFT_DROP];
    ALL_TAC] THEN
  REWRITE_TAC[HOMEOMORPHIC_MINIMAL; IN_INTERVAL_1; LIFT_DROP] THEN
  GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`f:num->real^1->real^1`; `g:num->real^1->real^1`] THEN
  DISCH_TAC THEN
  EXISTS_TAC
   `(\x. lambda i.
       drop((f:num->real^1->real^1) i (lift(x$i)))):real^N->real^N` THEN
  EXISTS_TAC
   `(\x. lambda i.
       drop((g:num->real^1->real^1) i (lift(x$i)))):real^N->real^N` THEN
  ASM_SIMP_TAC[IN_INTERVAL; LAMBDA_BETA; CART_EQ; LIFT_DROP] THEN
  ONCE_REWRITE_TAC[CONTINUOUS_ON_COMPONENTWISE_LIFT] THEN
  SIMP_TAC[LAMBDA_BETA; LIFT_DROP] THEN CONJ_TAC THEN REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[GSYM o_DEF] THEN
  MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_LIFT_COMPONENT] THEN
  MATCH_MP_TAC CONTINUOUS_ON_SUBSET THENL
   [EXISTS_TAC `interval(lift((a:real^N)$i),lift((b:real^N)$i))`;
    EXISTS_TAC `interval(lift((c:real^N)$i),lift((d:real^N)$i))`] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_INTERVAL_1] THEN
  ASM_SIMP_TAC[LIFT_DROP; IN_INTERVAL]);;


let HOMEOMORPHIC_OPEN_INTERVAL_UNIV = 
prove
 (`!a b:real^N.
        ~(interval(a,b) = {})
        ==> interval(a,b) homeomorphic (:real^N)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `!i. 1 <= i /\ i <= dimindex(:N)
        ==> interval(lift((a:real^N)$i),lift((b:real^N)$i)) homeomorphic
            (:real^1)`
  MP_TAC THENL
   [RULE_ASSUM_TAC(REWRITE_RULE[INTERVAL_NE_EMPTY]) THEN
    ASM_SIMP_TAC[HOMEOMORPHIC_OPEN_INTERVAL_UNIV_1; LIFT_DROP];
    ALL_TAC] THEN
  REWRITE_TAC[HOMEOMORPHIC_MINIMAL; IN_INTERVAL_1; LIFT_DROP] THEN
  GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM; IN_UNIV] THEN
  MAP_EVERY X_GEN_TAC [`f:num->real^1->real^1`; `g:num->real^1->real^1`] THEN
  DISCH_TAC THEN
  EXISTS_TAC
   `(\x. lambda i.
       drop((f:num->real^1->real^1) i (lift(x$i)))):real^N->real^N` THEN
  EXISTS_TAC
   `(\x. lambda i.
       drop((g:num->real^1->real^1) i (lift(x$i)))):real^N->real^N` THEN
  ASM_SIMP_TAC[IN_INTERVAL; LAMBDA_BETA; CART_EQ; LIFT_DROP; IN_UNIV] THEN
  ONCE_REWRITE_TAC[CONTINUOUS_ON_COMPONENTWISE_LIFT] THEN
  SIMP_TAC[LAMBDA_BETA; LIFT_DROP] THEN CONJ_TAC THEN REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[GSYM o_DEF] THEN
  MATCH_MP_TAC CONTINUOUS_ON_COMPOSE THEN
  ASM_SIMP_TAC[CONTINUOUS_ON_LIFT_COMPONENT] THEN
  MATCH_MP_TAC CONTINUOUS_ON_SUBSET THENL
   [EXISTS_TAC `interval(lift((a:real^N)$i),lift((b:real^N)$i))`;
    EXISTS_TAC `(:real^1)`] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_INTERVAL_1; IN_UNIV] THEN
  ASM_SIMP_TAC[LIFT_DROP; IN_INTERVAL]);;


let HOMEOMORPHIC_BALL_UNIV = 
prove
 (`!a:real^N r. &0 < r ==> ball(a,r) homeomorphic (:real^N)`,

  REPEAT GEN_TAC THEN GEOM_ORIGIN_TAC `a:real^N` THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `?y:real^N. r = norm(y)` (CHOOSE_THEN SUBST_ALL_TAC) THENL
   [ASM_MESON_TAC[VECTOR_CHOOSE_SIZE; REAL_LT_IMP_LE]; POP_ASSUM MP_TAC] THEN
  REWRITE_TAC[NORM_POS_LT] THEN GEOM_NORMALIZE_TAC `y:real^N` THEN
  SIMP_TAC[] THEN GEN_TAC THEN REPEAT(DISCH_THEN(K ALL_TAC)) THEN
  REWRITE_TAC[HOMEOMORPHIC_MINIMAL] THEN
  EXISTS_TAC `\z:real^N. inv(&1 - norm(z)) % z` THEN
  EXISTS_TAC `\z:real^N. inv(&1 + norm(z)) % z` THEN
  REWRITE_TAC[IN_BALL; IN_UNIV; DIST_0; VECTOR_MUL_ASSOC; VECTOR_MUL_EQ_0;
              VECTOR_ARITH `a % x:real^N = x <=> (a - &1) % x = vec 0`] THEN
  REPEAT CONJ_TAC THENL
   [X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN DISJ1_TAC THEN
    REWRITE_TAC[GSYM REAL_INV_MUL; REAL_SUB_0; REAL_INV_EQ_1] THEN
    REWRITE_TAC[NORM_MUL; REAL_ABS_INV] THEN
    ASM_SIMP_TAC[REAL_ARITH `x < &1 ==> abs(&1 - x) = &1 - x`] THEN
    POP_ASSUM MP_TAC THEN CONV_TAC REAL_FIELD;
    X_GEN_TAC `y:real^N` THEN REWRITE_TAC[NORM_MUL; REAL_ABS_INV] THEN
    ASM_SIMP_TAC[NORM_POS_LE; REAL_ARITH
     `&0 <= y ==> inv(abs(&1 + y)) * z = z / (&1 + y)`] THEN
    ASM_SIMP_TAC[NORM_POS_LE; REAL_LT_LDIV_EQ; REAL_ARITH
      `&0 <= y ==> &0 < &1 + y`] THEN
    CONJ_TAC THENL [REAL_ARITH_TAC; DISJ1_TAC] THEN
    REWRITE_TAC[GSYM REAL_INV_MUL; REAL_SUB_0; REAL_INV_EQ_1] THEN
    MP_TAC(ISPEC `y:real^N` NORM_POS_LE) THEN CONV_TAC REAL_FIELD;
    MATCH_MP_TAC CONTINUOUS_ON_MUL THEN REWRITE_TAC[CONTINUOUS_ON_ID] THEN
    GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM o_DEF] THEN
    MATCH_MP_TAC CONTINUOUS_ON_INV THEN
    SIMP_TAC[IN_BALL_0; REAL_SUB_0; REAL_ARITH `x < &1 ==> ~(&1 = x)`] THEN
    REWRITE_TAC[o_DEF; LIFT_SUB] THEN MATCH_MP_TAC CONTINUOUS_ON_SUB THEN
    REWRITE_TAC[CONTINUOUS_ON_CONST] THEN
    MATCH_MP_TAC CONTINUOUS_ON_LIFT_NORM_COMPOSE THEN
    REWRITE_TAC[CONTINUOUS_ON_ID];
    MATCH_MP_TAC CONTINUOUS_ON_MUL THEN REWRITE_TAC[CONTINUOUS_ON_ID] THEN
    GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM o_DEF] THEN
    MATCH_MP_TAC CONTINUOUS_ON_INV THEN
    SIMP_TAC[NORM_POS_LE; REAL_ARITH `&0 <= x ==> ~(&1 + x = &0)`] THEN
    REWRITE_TAC[o_DEF; LIFT_ADD] THEN MATCH_MP_TAC CONTINUOUS_ON_ADD THEN
    REWRITE_TAC[CONTINUOUS_ON_CONST] THEN
    MATCH_MP_TAC CONTINUOUS_ON_LIFT_NORM_COMPOSE THEN
    REWRITE_TAC[CONTINUOUS_ON_ID]]);;

(* ------------------------------------------------------------------------- *)
(* Cardinalities of various useful sets.                                     *)
(* ------------------------------------------------------------------------- *)


let CARD_EQ_EUCLIDEAN = 
prove
 (`(:real^N) =_c (:real)`,

  MATCH_MP_TAC CARD_EQ_CART THEN REWRITE_TAC[real_INFINITE]);;


let UNCOUNTABLE_EUCLIDEAN = 
prove
 (`~COUNTABLE(:real^N)`,

  MATCH_MP_TAC CARD_EQ_REAL_IMP_UNCOUNTABLE THEN
  REWRITE_TAC[CARD_EQ_EUCLIDEAN]);;


let CARD_EQ_INTERVAL = 
prove
 (`(!a b:real^N. ~(interval(a,b) = {}) ==> interval[a,b] =_c (:real)) /\
   (!a b:real^N. ~(interval(a,b) = {}) ==> interval(a,b) =_c (:real))`,

  REWRITE_TAC[AND_FORALL_THM] THEN REPEAT GEN_TAC THEN
  ASM_CASES_TAC `interval(a:real^N,b) = {}` THEN ASM_REWRITE_TAC[] THEN
  CONJ_TAC THEN REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
    REWRITE_TAC[CARD_LE_UNIV] THEN MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    REWRITE_TAC[CARD_EQ_EUCLIDEAN];
    TRANS_TAC CARD_LE_TRANS `interval(a:real^N,b)` THEN
    SIMP_TAC[CARD_LE_SUBSET; INTERVAL_OPEN_SUBSET_CLOSED];
    TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
    REWRITE_TAC[CARD_LE_UNIV] THEN MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    REWRITE_TAC[CARD_EQ_EUCLIDEAN];
    ALL_TAC] THEN
  TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
  SIMP_TAC[ONCE_REWRITE_RULE[CARD_EQ_SYM] CARD_EQ_IMP_LE;
           CARD_EQ_EUCLIDEAN] THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP HOMEOMORPHIC_OPEN_INTERVAL_UNIV) THEN
  DISCH_THEN(MP_TAC o MATCH_MP HOMEOMORPHIC_IMP_CARD_EQ) THEN
  MESON_TAC[CARD_EQ_IMP_LE; CARD_EQ_SYM]);;


let UNCOUNTABLE_INTERVAL = 
prove
 (`(!a b. ~(interval(a,b) = {}) ==> ~COUNTABLE(interval[a,b])) /\
   (!a b. ~(interval(a,b) = {}) ==> ~COUNTABLE(interval(a,b)))`,


let COUNTABLE_OPEN_INTERVAL = 
prove
 (`!a b. COUNTABLE(interval(a,b)) <=> interval(a,b) = {}`,


let CARD_EQ_OPEN = 
prove
 (`!s:real^N->bool. open s /\ ~(s = {}) ==> s =_c (:real)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
    REWRITE_TAC[CARD_LE_UNIV] THEN MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    REWRITE_TAC[CARD_EQ_EUCLIDEAN];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_CONTAINS_INTERVAL]) THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    DISCH_THEN(X_CHOOSE_TAC `c:real^N`) THEN
    DISCH_THEN(MP_TAC o SPEC `c:real^N`) THEN
    ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`] THEN
    ASM_CASES_TAC `interval(a:real^N,b) = {}` THEN
    ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN STRIP_TAC THEN
    TRANS_TAC CARD_LE_TRANS `interval[a:real^N,b]` THEN
    ASM_SIMP_TAC[CARD_LE_SUBSET] THEN MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    ONCE_REWRITE_TAC[CARD_EQ_SYM] THEN ASM_SIMP_TAC[CARD_EQ_INTERVAL]]);;


let UNCOUNTABLE_OPEN = 
prove
 (`!s:real^N->bool. open s /\ ~(s = {}) ==> ~(COUNTABLE s)`,


let CARD_EQ_BALL = 
prove
 (`!a:real^N r. &0 < r ==> ball(a,r) =_c (:real)`,


let CARD_EQ_CBALL = 
prove
 (`!a:real^N r. &0 < r ==> cball(a,r) =_c (:real)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
    REWRITE_TAC[CARD_LE_UNIV] THEN MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    REWRITE_TAC[CARD_EQ_EUCLIDEAN];
    TRANS_TAC CARD_LE_TRANS `ball(a:real^N,r)` THEN
    SIMP_TAC[CARD_LE_SUBSET; BALL_SUBSET_CBALL] THEN
    MATCH_MP_TAC CARD_EQ_IMP_LE THEN
    ONCE_REWRITE_TAC[CARD_EQ_SYM] THEN ASM_SIMP_TAC[CARD_EQ_BALL]]);;


let FINITE_IMP_NOT_OPEN = 
prove
 (`!s:real^N->bool. FINITE s /\ ~(s = {}) ==> ~(open s)`,


let OPEN_IMP_INFINITE = 
prove
 (`!s. open s ==> s = {} \/ INFINITE s`,


let EMPTY_INTERIOR_FINITE = 
prove
 (`!s:real^N->bool. FINITE s ==> interior s = {}`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPEC `s:real^N->bool` OPEN_INTERIOR) THEN
  ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] FINITE_IMP_NOT_OPEN) THEN
  MATCH_MP_TAC FINITE_SUBSET THEN EXISTS_TAC `s:real^N->bool` THEN
  ASM_REWRITE_TAC[INTERIOR_SUBSET]);;


let CARD_EQ_CONNECTED = 
prove
 (`!s a b:real^N.
        connected s /\ a IN s /\ b IN s /\ ~(a = b) ==> s =_c (:real)`,

  GEOM_ORIGIN_TAC `b:real^N` THEN GEOM_NORMALIZE_TAC `a:real^N` THEN
  REWRITE_TAC[NORM_EQ_SQUARE; REAL_POS; REAL_POW_ONE] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [TRANS_TAC CARD_LE_TRANS `(:real^N)` THEN
    SIMP_TAC[CARD_LE_UNIV; CARD_EQ_EUCLIDEAN; CARD_EQ_IMP_LE];
    TRANS_TAC CARD_LE_TRANS `interval[vec 0:real^1,vec 1]` THEN CONJ_TAC THENL
     [MATCH_MP_TAC(ONCE_REWRITE_RULE[CARD_EQ_SYM] CARD_EQ_IMP_LE) THEN
      SIMP_TAC[UNIT_INTERVAL_NONEMPTY; CARD_EQ_INTERVAL];
      REWRITE_TAC[LE_C] THEN EXISTS_TAC `\x:real^N. lift(a dot x)` THEN
      SIMP_TAC[FORALL_LIFT; LIFT_EQ; IN_INTERVAL_1; LIFT_DROP; DROP_VEC] THEN
      X_GEN_TAC `t:real` THEN STRIP_TAC THEN
      MATCH_MP_TAC CONNECTED_IVT_HYPERPLANE THEN
      MAP_EVERY EXISTS_TAC [`vec 0:real^N`; `a:real^N`] THEN
      ASM_REWRITE_TAC[DOT_RZERO]]]);;


let UNCOUNTABLE_CONNECTED = 
prove
 (`!s a b:real^N.
        connected s /\ a IN s /\ b IN s /\ ~(a = b) ==> ~COUNTABLE s`,

  REPEAT GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC CARD_EQ_REAL_IMP_UNCOUNTABLE THEN
  MATCH_MP_TAC CARD_EQ_CONNECTED THEN
  ASM_MESON_TAC[]);;


let CARD_LT_IMP_DISCONNECTED = 
prove
 (`!s x:real^N. s <_c (:real) /\ x IN s ==> connected_component s x = {x}`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[SET_RULE
   `s = {a} <=> a IN s /\ !a b. a IN s /\ b IN s /\ ~(a = b) ==> F`] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[IN] THEN
  ASM_REWRITE_TAC[CONNECTED_COMPONENT_REFL_EQ] THEN
  MP_TAC(ISPECL [`connected_component s (x:real^N)`; `a:real^N`; `b:real^N`]
        CARD_EQ_CONNECTED) THEN
  ASM_REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT] THEN
  DISCH_TAC THEN UNDISCH_TAC `(s:real^N->bool) <_c (:real)` THEN
  REWRITE_TAC[CARD_NOT_LT] THEN
  TRANS_TAC CARD_LE_TRANS `connected_component s (x:real^N)` THEN
  ASM_SIMP_TAC[ONCE_REWRITE_RULE[CARD_EQ_SYM] CARD_EQ_IMP_LE] THEN
  MATCH_MP_TAC CARD_LE_SUBSET THEN REWRITE_TAC[CONNECTED_COMPONENT_SUBSET]);;


let COUNTABLE_IMP_DISCONNECTED = 
prove
 (`!s x:real^N. COUNTABLE s /\ x IN s ==> connected_component s x = {x}`,


let CONNECTED_CARD_EQ_IFF_NONTRIVIAL = 
prove
 (`!s:real^N->bool.
        connected s ==> (s =_c (:real) <=> ~(?a. s SUBSET {a}))`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN REPEAT STRIP_TAC THENL
   [ALL_TAC; MATCH_MP_TAC CARD_EQ_CONNECTED THEN ASM SET_TAC[]] THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP(REWRITE_RULE[IMP_CONJ_ALT] FINITE_SUBSET)) THEN
  REWRITE_TAC[FINITE_SING] THEN
  ASM_MESON_TAC[CARD_EQ_REAL_IMP_UNCOUNTABLE; FINITE_IMP_COUNTABLE]);;

(* ------------------------------------------------------------------------- *)
(* "Iff" forms of constancy of function from connected set into a set that   *)
(* is smaller than R, or countable, or finite, or disconnected, or discrete. *)
(* ------------------------------------------------------------------------- *)

let [CONTINUOUS_DISCONNECTED_RANGE_CONSTANT_EQ;
     CONTINUOUS_DISCRETE_RANGE_CONSTANT_EQ;
     CONTINUOUS_FINITE_RANGE_CONSTANT_EQ] = (CONJUNCTS o prove)
  (`(!s. connected s <=>
         !f:real^M->real^N t.
            f continuous_on s /\ IMAGE f s SUBSET t /\
            (!y. y IN t ==> connected_component t y = {y})
            ==> ?a. !x. x IN s ==> f x = a) /\
    (!s. connected s <=>
         !f:real^M->real^N.
            f continuous_on s /\
            (!x. x IN s
                 ==> ?e. &0 < e /\
                         !y. y IN s /\ ~(f y = f x) ==> e <= norm(f y - f x))
            ==> ?a. !x. x IN s ==> f x = a) /\
    (!s. connected s <=>
         !f:real^M->real^N.
            f continuous_on s /\ FINITE(IMAGE f s)
            ==> ?a. !x. x IN s ==> f x = a)`,
  REWRITE_TAC[AND_FORALL_THM] THEN X_GEN_TAC `s:real^M->bool` THEN
  MATCH_MP_TAC(TAUT
   `(s ==> t) /\ (t ==> u) /\ (u ==> v) /\ (v ==> s)
    ==> (s <=> t) /\ (s <=> u) /\ (s <=> v)`) THEN
  REPEAT CONJ_TAC THENL
   [REPEAT STRIP_TAC THEN ASM_CASES_TAC `s:real^M->bool = {}` THEN
    ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
    FIRST_X_ASSUM(X_CHOOSE_TAC `x:real^M` o
        GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
    EXISTS_TAC `(f:real^M->real^N) x` THEN
    MATCH_MP_TAC(SET_RULE
     `IMAGE f s SUBSET {a} ==> !y. y IN s ==> f y = a`) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `(f:real^M->real^N) x`) THEN
    ANTS_TAC THENL [ASM SET_TAC[]; DISCH_THEN(SUBST1_TAC o SYM)] THEN
    MATCH_MP_TAC CONNECTED_COMPONENT_MAXIMAL THEN
    ASM_SIMP_TAC[CONNECTED_CONTINUOUS_IMAGE] THEN ASM SET_TAC[];
    REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
    EXISTS_TAC `IMAGE (f:real^M->real^N) s` THEN
    ASM_REWRITE_TAC[FORALL_IN_IMAGE; SUBSET_REFL] THEN
    X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^M`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
    MATCH_MP_TAC(SET_RULE
     `(!y. y IN s /\ f y IN connected_component (IMAGE f s) a ==> f y = a) /\
      connected_component (IMAGE f s) a SUBSET (IMAGE f s) /\
      connected_component (IMAGE f s) a a
      ==> connected_component (IMAGE f s) a = {a}`) THEN
    REWRITE_TAC[CONNECTED_COMPONENT_SUBSET; CONNECTED_COMPONENT_REFL_EQ] THEN
    ASM_SIMP_TAC[FUN_IN_IMAGE] THEN X_GEN_TAC `y:real^M` THEN STRIP_TAC THEN
    MP_TAC(ISPEC `connected_component (IMAGE (f:real^M->real^N) s) (f x)`
        CONNECTED_CLOSED) THEN
    REWRITE_TAC[CONNECTED_CONNECTED_COMPONENT] THEN
    ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
    ASM_REWRITE_TAC[] THEN MAP_EVERY EXISTS_TAC
     [`cball((f:real^M->real^N) x,e / &2)`;
      `(:real^N) DIFF ball((f:real^M->real^N) x,e)`] THEN
    REWRITE_TAC[GSYM OPEN_CLOSED; OPEN_BALL; CLOSED_CBALL] THEN
    REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN REPEAT CONJ_TAC THENL
     [REWRITE_TAC[SUBSET; IN_CBALL; IN_UNION; IN_DIFF; IN_BALL; IN_UNIV] THEN
      MATCH_MP_TAC(MESON[SUBSET; CONNECTED_COMPONENT_SUBSET]
       `(!x. x IN s ==> P x)
        ==> (!x. x IN connected_component s y ==> P x)`) THEN
      REWRITE_TAC[FORALL_IN_IMAGE] THEN X_GEN_TAC `z:real^M` THEN
      DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `z:real^M`) THEN
      ASM_REWRITE_TAC[] THEN CONV_TAC NORM_ARITH;
      MATCH_MP_TAC(SET_RULE
       `(!x. x IN s /\ x IN t ==> F) ==> s INTER t INTER u = {}`) THEN
      REWRITE_TAC[IN_BALL; IN_CBALL; IN_DIFF; IN_UNIV] THEN
      UNDISCH_TAC `&0 < e` THEN CONV_TAC NORM_ARITH;
      EXISTS_TAC `(f:real^M->real^N) x` THEN
      ASM_SIMP_TAC[CENTRE_IN_CBALL; REAL_HALF; REAL_LT_IMP_LE; IN_INTER] THEN
      REWRITE_TAC[IN] THEN
      ASM_SIMP_TAC[CONNECTED_COMPONENT_REFL_EQ; FUN_IN_IMAGE];
      EXISTS_TAC `(f:real^M->real^N) y` THEN
      ASM_REWRITE_TAC[IN_INTER; IN_DIFF; IN_UNIV; IN_BALL; REAL_NOT_LT] THEN
      ASM_SIMP_TAC[ONCE_REWRITE_RULE[DIST_SYM] dist]];
    MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `f:real^M->real^N` THEN
    DISCH_THEN(fun th -> STRIP_TAC THEN MATCH_MP_TAC th) THEN
    ASM_REWRITE_TAC[] THEN X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
    ASM_CASES_TAC `IMAGE (f:real^M->real^N) s DELETE (f x) = {}` THENL
     [EXISTS_TAC `&1` THEN REWRITE_TAC[REAL_LT_01] THEN ASM SET_TAC[];
      ALL_TAC] THEN
    EXISTS_TAC
     `inf{norm(z - f x) |z| z IN IMAGE (f:real^M->real^N) s DELETE (f x)}` THEN
    REWRITE_TAC[SIMPLE_IMAGE] THEN
    ASM_SIMP_TAC[REAL_LT_INF_FINITE; REAL_INF_LE_FINITE; FINITE_DELETE;
                 FINITE_IMAGE; IMAGE_EQ_EMPTY] THEN
    REWRITE_TAC[FORALL_IN_IMAGE; EXISTS_IN_IMAGE] THEN
    REWRITE_TAC[IN_DELETE; NORM_POS_LT; VECTOR_SUB_EQ; IN_IMAGE] THEN
    MESON_TAC[REAL_LE_REFL];
    REWRITE_TAC[CONNECTED_CLOSED_IN_EQ] THEN
    ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
    REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`t:real^M->bool`; `u:real^M->bool`] THEN
    STRIP_TAC THEN DISCH_THEN(MP_TAC o SPEC
     `(\x. if x IN t then vec 0 else basis 1):real^M->real^N`) THEN
    REWRITE_TAC[NOT_IMP] THEN REPEAT CONJ_TAC THENL
     [EXPAND_TAC "s" THEN MATCH_MP_TAC CONTINUOUS_ON_CASES_LOCAL THEN
      ASM_REWRITE_TAC[CONTINUOUS_ON_CONST] THEN ASM SET_TAC[];
      MATCH_MP_TAC FINITE_SUBSET THEN EXISTS_TAC `{vec 0:real^N,basis 1}` THEN
      REWRITE_TAC[FINITE_INSERT; FINITE_EMPTY] THEN SET_TAC[];
      SUBGOAL_THEN `?a b:real^M. a IN s /\ a IN t /\ b IN s /\ ~(b IN t)`
      STRIP_ASSUME_TAC THENL
       [ASM SET_TAC[]; DISCH_THEN(CHOOSE_THEN MP_TAC)] THEN
      DISCH_THEN(fun th -> MP_TAC(SPEC `a:real^M` th) THEN
                           MP_TAC(SPEC `b:real^M` th)) THEN
      ASM_REWRITE_TAC[] THEN DISCH_THEN(SUBST1_TAC o SYM) THEN
      CONV_TAC(RAND_CONV SYM_CONV) THEN
      SIMP_TAC[BASIS_NONZERO; LE_REFL; DIMINDEX_GE_1; REAL_LE_REFL]]]);;


let CONTINUOUS_DISCONNECTED_RANGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
        connected s /\
        f continuous_on s /\ IMAGE f s SUBSET t /\
        (!y. y IN t ==> connected_component t y = {y})
        ==> ?a. !x. x IN s ==> f x = a`,

  MESON_TAC[CONTINUOUS_DISCONNECTED_RANGE_CONSTANT_EQ]);;


let CONTINUOUS_DISCRETE_RANGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
        connected s /\
        f continuous_on s /\
        (!x. x IN s
             ==> ?e. &0 < e /\
                     !y. y IN s /\ ~(f y = f x) ==> e <= norm(f y - f x))
        ==> ?a. !x. x IN s ==> f x = a`,

  ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN
  REWRITE_TAC[RIGHT_FORALL_IMP_THM; IMP_CONJ] THEN
  REWRITE_TAC[IMP_IMP; GSYM CONTINUOUS_DISCRETE_RANGE_CONSTANT_EQ]);;


let CONTINUOUS_FINITE_RANGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
        connected s /\
        f continuous_on s /\
        FINITE(IMAGE f s)
        ==> ?a. !x. x IN s ==> f x = a`,

  MESON_TAC[CONTINUOUS_FINITE_RANGE_CONSTANT_EQ]);;


let CONTINUOUS_COUNTABLE_RANGE_CONSTANT_EQ = 
prove
 (`!s. connected s <=>
         !f:real^M->real^N.
            f continuous_on s /\ COUNTABLE(IMAGE f s)
            ==> ?a. !x. x IN s ==> f x = a`,

  GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[CONTINUOUS_DISCONNECTED_RANGE_CONSTANT_EQ];
    REWRITE_TAC[CONTINUOUS_FINITE_RANGE_CONSTANT_EQ]] THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[FINITE_IMP_COUNTABLE] THEN
  EXISTS_TAC `IMAGE (f:real^M->real^N) s` THEN
  ASM_SIMP_TAC[COUNTABLE_IMP_DISCONNECTED; SUBSET_REFL]);;


let CONTINUOUS_CARD_LT_RANGE_CONSTANT_EQ = 
prove
 (`!s. connected s <=>
         !f:real^M->real^N.
            f continuous_on s /\ (IMAGE f s) <_c (:real)
            ==> ?a. !x. x IN s ==> f x = a`,

  GEN_TAC THEN EQ_TAC THENL
   [REWRITE_TAC[CONTINUOUS_DISCONNECTED_RANGE_CONSTANT_EQ];
    REWRITE_TAC[CONTINUOUS_COUNTABLE_RANGE_CONSTANT_EQ]] THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_SIMP_TAC[COUNTABLE_IMP_CARD_LT_REAL] THEN
  EXISTS_TAC `IMAGE (f:real^M->real^N) s` THEN
  ASM_SIMP_TAC[CARD_LT_IMP_DISCONNECTED; SUBSET_REFL]);;


let CONTINUOUS_COUNTABLE_RANGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
        connected s /\ f continuous_on s /\ COUNTABLE(IMAGE f s)
        ==> ?a. !x. x IN s ==> f x = a`,


let CONTINUOUS_CARD_LT_RANGE_CONSTANT = 
prove
 (`!f:real^M->real^N s.
        connected s /\ f continuous_on s /\ (IMAGE f s) <_c (:real)
        ==> ?a. !x. x IN s ==> f x = a`,

(* ------------------------------------------------------------------------- *)
(* Homeomorphism of hyperplanes.                                             *)
(* ------------------------------------------------------------------------- *)


let HOMEOMORPHIC_HYPERPLANES = 
prove
 (`!a:real^N b c:real^N d.
        ~(a = vec 0) /\ ~(c = vec 0)
        ==> {x | a dot x = b} homeomorphic {x | c dot x = d}`,

  
let lemma = prove
   (`~(a = vec 0)
     ==> {x:real^N | a dot x = b} homeomorphic {x:real^N | x$1 = &0}`,
    REPEAT STRIP_TAC THEN SUBGOAL_THEN `?c:real^N. a dot c = b`
    STRIP_ASSUME_TAC THENL
     [FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [CART_EQ]) THEN
      REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; VEC_COMPONENT] THEN
      DISCH_THEN(X_CHOOSE_THEN `k:num` STRIP_ASSUME_TAC) THEN
      EXISTS_TAC `b / (a:real^N)$k % basis k:real^N` THEN
      ASM_SIMP_TAC[DOT_RMUL; DOT_BASIS; REAL_DIV_RMUL];
      FIRST_X_ASSUM(SUBST1_TAC o SYM) THEN
      ABBREV_TAC `p = {x:real^N | x$1 = &0}` THEN
      GEOM_ORIGIN_TAC `c:real^N` THEN
      REWRITE_TAC[VECTOR_ADD_RID; DOT_RADD; DOT_RZERO; REAL_EQ_ADD_LCANCEL_0;
                  REAL_ADD_RID] THEN
      REPEAT STRIP_TAC THEN UNDISCH_TAC `~(a:real^N = vec 0)` THEN
      GEOM_BASIS_MULTIPLE_TAC 1 `a:real^N` THEN
      SIMP_TAC[VECTOR_MUL_EQ_0; DE_MORGAN_THM; DOT_LMUL; REAL_ENTIRE] THEN
      SIMP_TAC[DOT_BASIS; LE_REFL; DIMINDEX_GE_1] THEN
      EXPAND_TAC "p" THEN REWRITE_TAC[HOMEOMORPHIC_REFL]]) in
  REPEAT STRIP_TAC THEN
  TRANS_TAC HOMEOMORPHIC_TRANS `{x:real^N | x$1 = &0}` THEN
  ASM_SIMP_TAC[lemma] THEN ONCE_REWRITE_TAC[HOMEOMORPHIC_SYM] THEN
  ASM_SIMP_TAC[lemma]);;


let HOMEOMORPHIC_HYPERPLANE_STANDARD_HYPERPLANE = 
prove
 (`!a:real^N b k c.
        ~(a = vec 0) /\ 1 <= k /\ k <= dimindex(:N)
        ==> {x | a dot x = b} homeomorphic {x:real^N | x$k = c}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `{x:real^N | x$k = c} = {x | basis k dot x = c}` SUBST1_TAC
  THENL [ASM_SIMP_TAC[DOT_BASIS]; MATCH_MP_TAC HOMEOMORPHIC_HYPERPLANES] THEN
  ASM_SIMP_TAC[BASIS_NONZERO]);;


let HOMEOMORPHIC_STANDARD_HYPERPLANE_HYPERPLANE = 
prove
 (`!a:real^N b k c.
        ~(a = vec 0) /\ 1 <= k /\ k <= dimindex(:N)
        ==> {x:real^N | x$k = c} homeomorphic {x | a dot x = b}`,

  ONCE_REWRITE_TAC[HOMEOMORPHIC_SYM] THEN
  REWRITE_TAC[HOMEOMORPHIC_HYPERPLANE_STANDARD_HYPERPLANE]);;


let HOMEOMORPHIC_HYPERPLANE_UNIV = 
prove
 (`!a b. ~(a = vec 0) /\ dimindex(:N) = dimindex(:M) + 1
         ==> {x:real^N | a dot x = b} homeomorphic (:real^M)`,

  REPEAT STRIP_TAC THEN TRANS_TAC HOMEOMORPHIC_TRANS
   `{x:real^N | basis(dimindex(:N)) dot x = &0}` THEN
  ASM_SIMP_TAC[HOMEOMORPHIC_HYPERPLANES; BASIS_NONZERO;
               LE_REFL; DIMINDEX_GE_1] THEN
  REWRITE_TAC[homeomorphic; HOMEOMORPHISM] THEN
  EXISTS_TAC `(\x. lambda i. x$i):real^N->real^M` THEN
  EXISTS_TAC `(\x. lambda i. if i <= dimindex(:M) then x$i else &0)
              :real^M->real^N` THEN
  REPEAT CONJ_TAC THENL
   [MATCH_MP_TAC LINEAR_CONTINUOUS_ON THEN
    SIMP_TAC[linear; CART_EQ; LAMBDA_BETA; VECTOR_ADD_COMPONENT;
             VECTOR_MUL_COMPONENT];
    REWRITE_TAC[SUBSET_UNIV];
    MATCH_MP_TAC LINEAR_CONTINUOUS_ON THEN
    SIMP_TAC[linear; CART_EQ; LAMBDA_BETA; VECTOR_ADD_COMPONENT;
             VECTOR_MUL_COMPONENT] THEN
    REPEAT STRIP_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
    REAL_ARITH_TAC;
    REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_ELIM_THM; IN_UNIV] THEN
    ASM_SIMP_TAC[DOT_BASIS; LAMBDA_BETA; LE_REFL; ARITH_RULE `1 <= n + 1`;
                 ARITH_RULE `~(m + 1 <= m)`];
    ASM_SIMP_TAC[IN_ELIM_THM; LAMBDA_BETA; DOT_BASIS; LE_REFL; CART_EQ;
                 ARITH_RULE `1 <= n + 1`] THEN
    GEN_TAC THEN DISCH_TAC THEN X_GEN_TAC `i:num` THEN
    ASM_CASES_TAC `i = dimindex(:M) + 1` THEN ASM_REWRITE_TAC[COND_ID] THEN
    COND_CASES_TAC THEN REWRITE_TAC[] THEN ASM_ARITH_TAC;
    ASM_SIMP_TAC[LAMBDA_BETA; CART_EQ; IN_UNIV; LE_REFL;
                 ARITH_RULE `i <= n ==> i <= n + 1`]]);;

(* ------------------------------------------------------------------------- *)
(* "Isometry" (up to constant bounds) of injective linear map etc.           *)
(* ------------------------------------------------------------------------- *)


let CAUCHY_ISOMETRIC = 
prove
 (`!f s e x.
        &0 < e /\ subspace s /\
        linear f /\ (!x. x IN s ==> norm(f x) >= e * norm(x)) /\
        (!n. x(n) IN s) /\ cauchy(f o x)
        ==> cauchy x`,

  REPEAT GEN_TAC THEN REWRITE_TAC[real_ge] THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[CAUCHY; dist; o_THM] THEN
  FIRST_ASSUM(fun th -> REWRITE_TAC[GSYM(MATCH_MP LINEAR_SUB th)]) THEN
  DISCH_THEN(fun th -> X_GEN_TAC `d:real` THEN DISCH_TAC THEN MP_TAC th) THEN
  DISCH_THEN(MP_TAC o SPEC `d * e`) THEN ASM_SIMP_TAC[REAL_LT_MUL] THEN
  ASM_MESON_TAC[REAL_LE_RDIV_EQ; REAL_MUL_SYM; REAL_LET_TRANS; SUBSPACE_SUB;
                REAL_LT_LDIV_EQ]);;


let COMPLETE_ISOMETRIC_IMAGE = 
prove
 (`!f:real^M->real^N s e.
        &0 < e /\ subspace s /\
        linear f /\ (!x. x IN s ==> norm(f x) >= e * norm(x)) /\
        complete s
        ==> complete(IMAGE f s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[complete; EXISTS_IN_IMAGE] THEN
  STRIP_TAC THEN X_GEN_TAC `g:num->real^N` THEN
  REWRITE_TAC[IN_IMAGE; SKOLEM_THM; FORALL_AND_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
  DISCH_THEN(X_CHOOSE_THEN `x:num->real^M` MP_TAC) THEN
  GEN_REWRITE_TAC (LAND_CONV o LAND_CONV) [GSYM FUN_EQ_THM] THEN
  REWRITE_TAC[GSYM o_DEF] THEN
  DISCH_THEN(CONJUNCTS_THEN2 SUBST_ALL_TAC ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:num->real^M`) THEN
  ASM_MESON_TAC[CAUCHY_ISOMETRIC; LINEAR_CONTINUOUS_AT;
                CONTINUOUS_AT_SEQUENTIALLY]);;


let INJECTIVE_IMP_ISOMETRIC = 
prove
 (`!f:real^M->real^N s.
        closed s /\ subspace s /\
        linear f /\ (!x. x IN s /\ (f x = vec 0) ==> (x = vec 0))
        ==> ?e. &0 < e /\ !x. x IN s ==> norm(f x) >= e * norm(x)`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s SUBSET {vec 0 :real^M}` THENL
   [EXISTS_TAC `&1` THEN REWRITE_TAC[REAL_LT_01; REAL_MUL_LID; real_ge] THEN
    ASM_MESON_TAC[SUBSET; IN_SING; NORM_0; LINEAR_0; REAL_LE_REFL];
    ALL_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [SUBSET]) THEN
  REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; IN_SING] THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^M` STRIP_ASSUME_TAC) THEN
  MP_TAC(ISPECL
   [`{(f:real^M->real^N) x | x IN s /\ norm(x) = norm(a:real^M)}`;
    `vec 0:real^N`] DISTANCE_ATTAINS_INF) THEN
  ANTS_TAC THENL
   [REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; IN_ELIM_THM] THEN
    CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
    MATCH_MP_TAC COMPACT_IMP_CLOSED THEN
    SUBST1_TAC(SET_RULE
     `{f x | x IN s /\ norm(x) = norm(a:real^M)} =
      IMAGE (f:real^M->real^N) (s INTER {x | norm x = norm a})`) THEN
    MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
    ASM_SIMP_TAC[LINEAR_CONTINUOUS_ON] THEN
    MATCH_MP_TAC CLOSED_INTER_COMPACT THEN ASM_REWRITE_TAC[] THEN
    SUBGOAL_THEN
     `{x:real^M | norm x = norm(a:real^M)} = frontier(cball(vec 0,norm a))`
    SUBST1_TAC THENL
     [ASM_SIMP_TAC[FRONTIER_CBALL; NORM_POS_LT; dist; VECTOR_SUB_LZERO;
                   NORM_NEG; sphere];
      ASM_SIMP_TAC[COMPACT_FRONTIER; COMPACT_CBALL]];
    ALL_TAC] THEN
  ONCE_REWRITE_TAC[SET_RULE `{f x | P x} = IMAGE f {x | P x}`] THEN
  REWRITE_TAC[FORALL_IN_IMAGE; EXISTS_IN_IMAGE] THEN
  DISCH_THEN(X_CHOOSE_THEN `b:real^M` MP_TAC) THEN
  REWRITE_TAC[IN_ELIM_THM; dist; VECTOR_SUB_LZERO; NORM_NEG] THEN
  STRIP_TAC THEN REWRITE_TAC[CLOSED_LIMPT; LIMPT_APPROACHABLE] THEN
  EXISTS_TAC `norm((f:real^M->real^N) b) / norm(b)` THEN CONJ_TAC THENL
   [ASM_MESON_TAC[REAL_LT_DIV; NORM_POS_LT; NORM_EQ_0]; ALL_TAC] THEN
  X_GEN_TAC `x:real^M` THEN DISCH_TAC THEN
  ASM_CASES_TAC `x:real^M = vec 0` THENL
   [FIRST_ASSUM(fun th -> ASM_REWRITE_TAC[MATCH_MP LINEAR_0 th]) THEN
    REWRITE_TAC[NORM_0; REAL_MUL_RZERO; real_ge; REAL_LE_REFL];
    ALL_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `(norm(a:real^M) / norm(x)) % x:real^M`) THEN
  ANTS_TAC THENL
   [ASM_SIMP_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM] THEN
    ASM_SIMP_TAC[REAL_DIV_RMUL; NORM_EQ_0] THEN ASM_MESON_TAC[subspace];
    ALL_TAC] THEN
  FIRST_ASSUM(fun th -> REWRITE_TAC[MATCH_MP LINEAR_CMUL th]) THEN
  ASM_REWRITE_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM; real_ge] THEN
  ASM_SIMP_TAC[GSYM REAL_LE_RDIV_EQ; REAL_LE_LDIV_EQ; NORM_POS_LT] THEN
  REWRITE_TAC[real_div; REAL_MUL_AC]);;


let CLOSED_INJECTIVE_IMAGE_SUBSPACE = 
prove
 (`!f s. subspace s /\
         linear f /\
         (!x. x IN s /\ f(x) = vec 0 ==> x = vec 0) /\
         closed s
         ==> closed(IMAGE f s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM COMPLETE_EQ_CLOSED] THEN
  MATCH_MP_TAC COMPLETE_ISOMETRIC_IMAGE THEN
  ASM_REWRITE_TAC[COMPLETE_EQ_CLOSED] THEN
  MATCH_MP_TAC INJECTIVE_IMP_ISOMETRIC THEN
  ASM_REWRITE_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* Relating linear images to open/closed/interior/closure.                   *)
(* ------------------------------------------------------------------------- *)


let OPEN_SURJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N.
        linear f /\ (!y. ?x. f x = y)
        ==> !s. open s ==> open(IMAGE f s)`,

  GEN_TAC THEN STRIP_TAC THEN
  REWRITE_TAC[open_def; FORALL_IN_IMAGE] THEN
  FIRST_ASSUM(MP_TAC o GEN `k:num` o SPEC `basis k:real^N`) THEN
  REWRITE_TAC[SKOLEM_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `b:num->real^M` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `bounded(IMAGE (b:num->real^M) (1..dimindex(:N)))` MP_TAC THENL
   [SIMP_TAC[FINITE_IMP_BOUNDED; FINITE_IMAGE; FINITE_NUMSEG]; ALL_TAC] THEN
  REWRITE_TAC[BOUNDED_POS; FORALL_IN_IMAGE; IN_NUMSEG] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  X_GEN_TAC `s:real^M->bool` THEN MATCH_MP_TAC MONO_FORALL THEN
  X_GEN_TAC `x:real^M` THEN ASM_CASES_TAC `(x:real^M) IN s` THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `e / B / &(dimindex(:N))` THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; DIMINDEX_GE_1; LE_1] THEN
  X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN REWRITE_TAC[IN_IMAGE] THEN
  ABBREV_TAC `u = y - (f:real^M->real^N) x` THEN
  EXISTS_TAC `x + vsum(1..dimindex(:N)) (\i. (u:real^N)$i % b i):real^M` THEN
  ASM_SIMP_TAC[LINEAR_ADD; LINEAR_VSUM; FINITE_NUMSEG; o_DEF;
               LINEAR_CMUL; BASIS_EXPANSION] THEN
  CONJ_TAC THENL [EXPAND_TAC "u" THEN VECTOR_ARITH_TAC; ALL_TAC] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN
  REWRITE_TAC[NORM_ARITH `dist(x + y,x) = norm y`] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `(dist(y,(f:real^M->real^N) x) * &(dimindex(:N))) * B` THEN
  ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ; REAL_OF_NUM_LT; DIMINDEX_GE_1; LE_1] THEN
  MATCH_MP_TAC VSUM_NORM_TRIANGLE THEN REWRITE_TAC[FINITE_NUMSEG] THEN
  ONCE_REWRITE_TAC[REAL_ARITH `(a * b) * c:real = b * a * c`] THEN
  GEN_REWRITE_TAC(RAND_CONV o LAND_CONV o RAND_CONV) [GSYM CARD_NUMSEG_1] THEN
  MATCH_MP_TAC SUM_BOUND THEN REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN
  X_GEN_TAC `k:num` THEN STRIP_TAC THEN REWRITE_TAC[NORM_MUL; dist] THEN
  MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS; NORM_POS_LE] THEN
  ASM_SIMP_TAC[COMPONENT_LE_NORM]);;


let OPEN_BIJECTIVE_LINEAR_IMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y) /\ (!y. ?x. f x = y)
        ==> (open(IMAGE f s) <=> open s)`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [DISCH_TAC; ASM_MESON_TAC[OPEN_SURJECTIVE_LINEAR_IMAGE]] THEN
  SUBGOAL_THEN `s = {x | (f:real^M->real^N) x IN IMAGE f s}`
  SUBST1_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC CONTINUOUS_OPEN_PREIMAGE_UNIV THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_AT]);;

add_linear_invariants [OPEN_BIJECTIVE_LINEAR_IMAGE_EQ];;


let CLOSED_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> !s. closed s ==> closed(IMAGE f s)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPEC `f:real^M->real^N` LINEAR_INJECTIVE_LEFT_INVERSE) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `g:real^N->real^M` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC CLOSED_IN_CLOSED_TRANS THEN
  EXISTS_TAC `IMAGE (f:real^M->real^N) (:real^M)` THEN
  CONJ_TAC THENL
   [MP_TAC(ISPECL [`g:real^N->real^M`; `IMAGE (f:real^M->real^N) (:real^M)`;
                   `IMAGE (g:real^N->real^M) (IMAGE (f:real^M->real^N) s)`]
        CONTINUOUS_CLOSED_IN_PREIMAGE) THEN
    ASM_SIMP_TAC[LINEAR_CONTINUOUS_ON] THEN ANTS_TAC THENL
     [ASM_REWRITE_TAC[GSYM IMAGE_o; IMAGE_I]; ALL_TAC] THEN
    MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [FUN_EQ_THM]) THEN
    REWRITE_TAC[EXTENSION; o_THM; I_THM] THEN SET_TAC[];
    MATCH_MP_TAC CLOSED_INJECTIVE_IMAGE_SUBSPACE THEN
    ASM_REWRITE_TAC[IN_UNIV; SUBSPACE_UNIV; CLOSED_UNIV] THEN
    X_GEN_TAC `x:real^M` THEN
    DISCH_THEN(MP_TAC o AP_TERM `g:real^N->real^M`) THEN
    RULE_ASSUM_TAC(REWRITE_RULE[FUN_EQ_THM; I_THM; o_THM]) THEN
    ASM_MESON_TAC[LINEAR_0]]);;


let CLOSED_INJECTIVE_LINEAR_IMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> (closed(IMAGE f s) <=> closed s)`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [DISCH_TAC; ASM_MESON_TAC[CLOSED_INJECTIVE_LINEAR_IMAGE]] THEN
  SUBGOAL_THEN `s = {x | (f:real^M->real^N) x IN IMAGE f s}`
  SUBST1_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE_UNIV THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_AT]);;

add_linear_invariants [CLOSED_INJECTIVE_LINEAR_IMAGE_EQ];;


let CLOSURE_LINEAR_IMAGE_SUBSET = 
prove
 (`!f:real^M->real^N s.
        linear f ==> IMAGE f (closure s) SUBSET closure(IMAGE f s)`,

  REPEAT STRIP_TAC THEN
  MATCH_MP_TAC IMAGE_CLOSURE_SUBSET THEN
  ASM_SIMP_TAC[CLOSED_CLOSURE; CLOSURE_SUBSET; LINEAR_CONTINUOUS_ON]);;


let CLOSURE_INJECTIVE_LINEAR_IMAGE  = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> closure(IMAGE f s) = IMAGE f (closure s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  ASM_SIMP_TAC[CLOSURE_LINEAR_IMAGE_SUBSET] THEN
  MATCH_MP_TAC CLOSURE_MINIMAL THEN
  SIMP_TAC[CLOSURE_SUBSET; IMAGE_SUBSET] THEN
  ASM_MESON_TAC[CLOSED_INJECTIVE_LINEAR_IMAGE; CLOSED_CLOSURE]);;

add_linear_invariants [CLOSURE_INJECTIVE_LINEAR_IMAGE];;


let CLOSURE_BOUNDED_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s.
        linear f /\ bounded s
        ==> closure(IMAGE f s) = IMAGE f (closure s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN
  ASM_SIMP_TAC[CLOSURE_LINEAR_IMAGE_SUBSET] THEN
  MATCH_MP_TAC CLOSURE_MINIMAL THEN
  SIMP_TAC[CLOSURE_SUBSET; IMAGE_SUBSET] THEN
  MATCH_MP_TAC COMPACT_IMP_CLOSED THEN
  MATCH_MP_TAC COMPACT_LINEAR_IMAGE THEN
  ASM_REWRITE_TAC[COMPACT_CLOSURE]);;


let LINEAR_INTERIOR_IMAGE_SUBSET = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
       ==> interior(IMAGE f s) SUBSET IMAGE f (interior s)`,


let LINEAR_IMAGE_SUBSET_INTERIOR = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!y. ?x. f x = y)
        ==> IMAGE f (interior s) SUBSET interior(IMAGE f s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INTERIOR_MAXIMAL THEN
  ASM_SIMP_TAC[OPEN_SURJECTIVE_LINEAR_IMAGE; OPEN_INTERIOR;
               IMAGE_SUBSET; INTERIOR_SUBSET]);;


let INTERIOR_BIJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y) /\ (!y. ?x. f x = y)
        ==> interior(IMAGE f s) = IMAGE f (interior s)`,

  REWRITE_TAC[interior] THEN GEOM_TRANSFORM_TAC[]);;

add_linear_invariants [INTERIOR_BIJECTIVE_LINEAR_IMAGE];;


let FRONTIER_BIJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y) /\ (!y. ?x. f x = y)
        ==> frontier(IMAGE f s) = IMAGE f (frontier s)`,

  REWRITE_TAC[frontier] THEN GEOM_TRANSFORM_TAC[]);;

add_linear_invariants [FRONTIER_BIJECTIVE_LINEAR_IMAGE];;

(* ------------------------------------------------------------------------- *)
(* Corollaries, reformulations and special cases for M = N.                  *)
(* ------------------------------------------------------------------------- *)


let IN_INTERIOR_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N g s x.
        linear f /\ linear g /\ (f o g = I) /\ x IN interior s
        ==> (f x) IN interior (IMAGE f s)`,

  REWRITE_TAC[FUN_EQ_THM; o_THM; I_THM] THEN REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:real^M->real^N`; `s:real^M->bool`]
    LINEAR_IMAGE_SUBSET_INTERIOR) THEN
  ASM_REWRITE_TAC[SUBSET; FORALL_IN_IMAGE] THEN
  ASM_MESON_TAC[]);;


let LINEAR_OPEN_MAPPING = 
prove
 (`!f:real^M->real^N g.
        linear f /\ linear g /\ (f o g = I)
        ==> !s. open s ==> open(IMAGE f s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[FUN_EQ_THM; o_THM; I_THM] THEN DISCH_TAC THEN
  MATCH_MP_TAC OPEN_SURJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[]);;


let INTERIOR_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> interior(IMAGE f s) = IMAGE f (interior s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INTERIOR_BIJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[LINEAR_INJECTIVE_IMP_SURJECTIVE]);;


let INTERIOR_SURJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ (!y. ?x. f x = y)
        ==> interior(IMAGE f s) = IMAGE f (interior s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INTERIOR_BIJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[LINEAR_SURJECTIVE_IMP_INJECTIVE]);;


let CLOSURE_SURJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ (!y. ?x. f x = y)
        ==> closure(IMAGE f s) = IMAGE f (closure s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSURE_INJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[LINEAR_SURJECTIVE_IMP_INJECTIVE]);;


let FRONTIER_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> frontier(IMAGE f s) = IMAGE f (frontier s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC FRONTIER_BIJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[LINEAR_INJECTIVE_IMP_SURJECTIVE]);;


let FRONTIER_SURJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^N->real^N.
        linear f /\ (!y. ?x. f x = y)
        ==> frontier(IMAGE f s) = IMAGE f (frontier s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC FRONTIER_BIJECTIVE_LINEAR_IMAGE THEN
  ASM_MESON_TAC[LINEAR_SURJECTIVE_IMP_INJECTIVE]);;


let COMPLETE_INJECTIVE_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> !s. complete s ==> complete(IMAGE f s)`,


let COMPLETE_INJECTIVE_LINEAR_IMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> (complete(IMAGE f s) <=> complete s)`,

add_linear_invariants [COMPLETE_INJECTIVE_LINEAR_IMAGE_EQ];;


let LIMPT_INJECTIVE_LINEAR_IMAGE_EQ = 
prove
 (`!f:real^M->real^N s.
        linear f /\ (!x y. f x = f y ==> x = y)
        ==> ((f x) limit_point_of (IMAGE f s) <=> x limit_point_of s)`,

  REWRITE_TAC[LIMPT_APPROACHABLE; EXISTS_IN_IMAGE] THEN
  REPEAT STRIP_TAC THEN EQ_TAC THEN DISCH_TAC THEN X_GEN_TAC `e:real` THEN
  DISCH_TAC THENL
   [MP_TAC(ISPEC `f:real^M->real^N` LINEAR_INJECTIVE_BOUNDED_BELOW_POS);
    MP_TAC(ISPEC `f:real^M->real^N` LINEAR_BOUNDED_POS)] THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THENL
   [FIRST_X_ASSUM(MP_TAC o SPEC `e * B:real`);
    FIRST_X_ASSUM(MP_TAC o SPEC `e / B:real`)] THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_LT_MUL; dist; GSYM LINEAR_SUB] THEN
  MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
  REPEAT(MATCH_MP_TAC MONO_AND THEN
         CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC]) THEN
  ASM_SIMP_TAC[GSYM REAL_LT_LDIV_EQ; REAL_LT_RDIV_EQ] THEN
  MATCH_MP_TAC(REAL_ARITH `a <= b ==> b < x ==> a < x`) THEN
  ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN ASM_SIMP_TAC[REAL_LE_RDIV_EQ]);;

add_linear_invariants [LIMPT_INJECTIVE_LINEAR_IMAGE_EQ];;


let LIMPT_TRANSLATION_EQ = 
prove
 (`!a s x. (a + x) limit_point_of (IMAGE (\y. a + y) s) <=> x limit_point_of s`,

  REWRITE_TAC[limit_point_of] THEN GEOM_TRANSLATE_TAC[]);;

add_translation_invariants [LIMPT_TRANSLATION_EQ];;


let OPEN_OPEN_LEFT_PROJECTION = 
prove
 (`!s t:real^(M,N)finite_sum->bool.
        open s /\ open t ==> open {x | x IN s /\ ?y. pastecart x y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `{x | x IN s /\ ?y. (pastecart x y:real^(M,N)finite_sum) IN t} =
    s INTER IMAGE fstcart t`
  SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_INTER; IN_IMAGE] THEN
    MESON_TAC[FSTCART_PASTECART; PASTECART_FST_SND];
    MATCH_MP_TAC OPEN_INTER THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_IMP; RIGHT_IMP_FORALL_THM]
      OPEN_SURJECTIVE_LINEAR_IMAGE) THEN
    ASM_REWRITE_TAC[LINEAR_FSTCART] THEN MESON_TAC[FSTCART_PASTECART]]);;


let OPEN_OPEN_RIGHT_PROJECTION = 
prove
 (`!s t:real^(M,N)finite_sum->bool.
        open s /\ open t ==> open {y | y IN s /\ ?x. pastecart x y IN t}`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `{y | y IN s /\ ?x. (pastecart x y:real^(M,N)finite_sum) IN t} =
    s INTER IMAGE sndcart t`
  SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_INTER; IN_IMAGE] THEN
    MESON_TAC[SNDCART_PASTECART; PASTECART_FST_SND];
    MATCH_MP_TAC OPEN_INTER THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_IMP; RIGHT_IMP_FORALL_THM]
      OPEN_SURJECTIVE_LINEAR_IMAGE) THEN
    ASM_REWRITE_TAC[LINEAR_SNDCART] THEN MESON_TAC[SNDCART_PASTECART]]);;

(* ------------------------------------------------------------------------- *)
(* Even more special cases.                                                  *)
(* ------------------------------------------------------------------------- *)


let INTERIOR_NEGATIONS = 
prove
 (`!s. interior(IMAGE (--) s) = IMAGE (--) (interior s)`,

  GEN_TAC THEN MATCH_MP_TAC INTERIOR_INJECTIVE_LINEAR_IMAGE THEN
  REWRITE_TAC[linear] THEN REPEAT CONJ_TAC THEN VECTOR_ARITH_TAC);;


let SYMMETRIC_INTERIOR = 
prove
 (`!s:real^N->bool.
        (!x. x IN s ==> --x IN s)
        ==> !x. x IN interior s ==> (--x) IN interior s`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP(ISPEC `(--):real^N->real^N` FUN_IN_IMAGE)) THEN
  REWRITE_TAC[GSYM INTERIOR_NEGATIONS] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_IMAGE] THEN ASM_MESON_TAC[VECTOR_NEG_NEG]);;


let CLOSURE_NEGATIONS = 
prove
 (`!s. closure(IMAGE (--) s) = IMAGE (--) (closure s)`,

  GEN_TAC THEN MATCH_MP_TAC CLOSURE_INJECTIVE_LINEAR_IMAGE THEN
  REWRITE_TAC[linear] THEN REPEAT CONJ_TAC THEN VECTOR_ARITH_TAC);;


let SYMMETRIC_CLOSURE = 
prove
 (`!s:real^N->bool.
        (!x. x IN s ==> --x IN s)
        ==> !x. x IN closure s ==> (--x) IN closure s`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP(ISPEC `(--):real^N->real^N` FUN_IN_IMAGE)) THEN
  REWRITE_TAC[GSYM CLOSURE_NEGATIONS] THEN
  MATCH_MP_TAC EQ_IMP THEN AP_TERM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_IMAGE] THEN ASM_MESON_TAC[VECTOR_NEG_NEG]);;

(* ------------------------------------------------------------------------- *)
(* Some properties of a canonical subspace.                                  *)
(* ------------------------------------------------------------------------- *)


let SUBSPACE_SUBSTANDARD = 
prove
 (`!d. subspace
         {x:real^N | !i. d < i /\ i <= dimindex(:N) ==> x$i = &0}`,

  GEN_TAC THEN ASM_CASES_TAC `d <= dimindex(:N)` THENL
   [MP_TAC(ARITH_RULE `!i. d < i ==> 1 <= i`) THEN
    SIMP_TAC[subspace; IN_ELIM_THM; REAL_MUL_RZERO; REAL_ADD_LID;
             VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT; VEC_COMPONENT];
    ASM_SIMP_TAC[ARITH_RULE `~(d:num <= e) ==> (d < i /\ i <= e <=> F)`] THEN
    REWRITE_TAC[SET_RULE `{x | T} = UNIV`; SUBSPACE_UNIV]]);;


let CLOSED_SUBSTANDARD = 
prove
 (`!d. closed
        {x:real^N | !i. d < i /\ i <= dimindex(:N) ==> x$i = &0}`,

  GEN_TAC THEN
  SUBGOAL_THEN
   `{x:real^N | !i. d < i /\ i <= dimindex(:N) ==> x$i = &0} =
    INTERS {{x | basis i dot x = &0} | d < i /\ i <= dimindex(:N)}`
  SUBST1_TAC THENL
   [ALL_TAC;
    SIMP_TAC[CLOSED_INTERS; CLOSED_HYPERPLANE; IN_ELIM_THM;
             LEFT_IMP_EXISTS_THM]] THEN
  GEN_REWRITE_TAC I [EXTENSION] THEN REWRITE_TAC[IN_INTERS; IN_ELIM_THM] THEN
  SIMP_TAC[LEFT_IMP_EXISTS_THM; IN_ELIM_THM] THEN
  MP_TAC(ARITH_RULE `!i. d < i ==> 1 <= i`) THEN
  SIMP_TAC[DOT_BASIS] THEN MESON_TAC[]);;


let DIM_SUBSTANDARD = 
prove
 (`!d. d <= dimindex(:N)
       ==> (dim {x:real^N | !i. d < i /\ i <= dimindex(:N)
                                ==> x$i = &0} =
            d)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC DIM_UNIQUE THEN
  EXISTS_TAC `IMAGE (basis:num->real^N) (1..d)` THEN REPEAT CONJ_TAC THENL
   [REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_ELIM_THM; IN_NUMSEG] THEN
    MESON_TAC[BASIS_COMPONENT; ARITH_RULE `d < i ==> 1 <= i`; NOT_LT];
    ALL_TAC;
    MATCH_MP_TAC INDEPENDENT_MONO THEN
    EXISTS_TAC `{basis i :real^N | 1 <= i /\ i <= dimindex(:N)}` THEN
    REWRITE_TAC[INDEPENDENT_STDBASIS]THEN
    REWRITE_TAC[SUBSET; FORALL_IN_IMAGE; IN_ELIM_THM; IN_NUMSEG] THEN
    ASM_MESON_TAC[LE_TRANS];
    MATCH_MP_TAC HAS_SIZE_IMAGE_INJ THEN REWRITE_TAC[HAS_SIZE_NUMSEG_1] THEN
    REWRITE_TAC[IN_NUMSEG] THEN ASM_MESON_TAC[LE_TRANS; BASIS_INJ]] THEN
  POP_ASSUM MP_TAC THEN SPEC_TAC(`d:num`,`d:num`) THEN
  INDUCT_TAC THENL
   [REWRITE_TAC[ARITH_RULE `0 < i <=> 1 <= i`; SPAN_STDBASIS] THEN
    SUBGOAL_THEN `IMAGE basis (1 .. 0) :real^N->bool = {}` SUBST1_TAC THENL
     [REWRITE_TAC[IMAGE_EQ_EMPTY; NUMSEG_EMPTY; ARITH]; ALL_TAC] THEN
    DISCH_TAC THEN REWRITE_TAC[SPAN_EMPTY; SUBSET; IN_ELIM_THM; IN_SING] THEN
    SIMP_TAC[CART_EQ; VEC_COMPONENT];
    ALL_TAC] THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o check (is_imp o concl)) THEN
  ASM_SIMP_TAC[ARITH_RULE `SUC d <= n ==> d <= n`] THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN DISCH_TAC THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x - (x$(SUC d)) % basis(SUC d) :real^N`) THEN
  ANTS_TAC THENL
   [X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    FIRST_ASSUM(ASSUME_TAC o MATCH_MP(ARITH_RULE `d < i ==> 1 <= i`)) THEN
    ASM_SIMP_TAC[VECTOR_SUB_COMPONENT; VECTOR_MUL_COMPONENT] THEN
    ASM_SIMP_TAC[BASIS_COMPONENT] THEN COND_CASES_TAC THEN
    ASM_REWRITE_TAC[REAL_MUL_RID; REAL_SUB_REFL] THEN
    ASM_REWRITE_TAC[REAL_MUL_RZERO; REAL_SUB_RZERO] THEN
    ASM_MESON_TAC[ARITH_RULE `d < i /\ ~(i = SUC d) ==> SUC d < i`];
    ALL_TAC] THEN
  DISCH_TAC THEN
  SUBST1_TAC(VECTOR_ARITH
   `x = (x - (x$(SUC d)) % basis(SUC d)) +
        x$(SUC d) % basis(SUC d) :real^N`) THEN
  MATCH_MP_TAC SPAN_ADD THEN CONJ_TAC THENL
   [ASM_MESON_TAC[SPAN_MONO; SUBSET_IMAGE; SUBSET; SUBSET_NUMSEG; LE_REFL; LE];
    MATCH_MP_TAC SPAN_MUL THEN MATCH_MP_TAC SPAN_SUPERSET THEN
    REWRITE_TAC[IN_IMAGE; IN_NUMSEG] THEN
    MESON_TAC[LE_REFL; ARITH_RULE `1 <= SUC d`]]);;

(* ------------------------------------------------------------------------- *)
(* Hence closure and completeness of all subspaces.                          *)
(* ------------------------------------------------------------------------- *)


let CLOSED_SUBSPACE = 
prove
 (`!s:real^N->bool. subspace s ==> closed s`,

  REPEAT STRIP_TAC THEN ABBREV_TAC `d = dim(s:real^N->bool)` THEN
  MP_TAC(MATCH_MP DIM_SUBSTANDARD
    (ISPEC `s:real^N->bool` DIM_SUBSET_UNIV)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
  MP_TAC(ISPECL
   [`{x:real^N | !i. d < i /\ i <= dimindex(:N)
                                ==> x$i = &0}`;
    `s:real^N->bool`] SUBSPACE_ISOMORPHISM) THEN
  ASM_REWRITE_TAC[SUBSPACE_SUBSTANDARD] THEN
  DISCH_THEN(X_CHOOSE_THEN `f:real^N->real^N` MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  DISCH_THEN(CONJUNCTS_THEN2 (SUBST_ALL_TAC o SYM) STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC(ISPEC `f:real^N->real^N` CLOSED_INJECTIVE_IMAGE_SUBSPACE) THEN
  ASM_REWRITE_TAC[SUBSPACE_SUBSTANDARD; CLOSED_SUBSTANDARD] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  ASM_REWRITE_TAC[] THEN
  CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[LINEAR_0]] THEN
  REWRITE_TAC[IN_ELIM_THM] THEN
  ASM_MESON_TAC[VEC_COMPONENT; ARITH_RULE `d < i ==> 1 <= i`]);;


let COMPLETE_SUBSPACE = 
prove
 (`!s:real^N->bool. subspace s ==> complete s`,


let CLOSED_SPAN = 
prove
 (`!s. closed(span s)`,


let DIM_CLOSURE = 
prove
 (`!s:real^N->bool. dim(closure s) = dim s`,

  GEN_TAC THEN REWRITE_TAC[GSYM LE_ANTISYM] THEN CONJ_TAC THENL
   [GEN_REWRITE_TAC RAND_CONV [GSYM DIM_SPAN]; ALL_TAC] THEN
  MATCH_MP_TAC DIM_SUBSET THEN REWRITE_TAC[CLOSURE_SUBSET] THEN
  MATCH_MP_TAC CLOSURE_MINIMAL THEN
  SIMP_TAC[CLOSED_SUBSPACE; SUBSPACE_SPAN; SPAN_INC]);;


let CLOSED_BOUNDEDPREIM_CONTINUOUS_IMAGE = 
prove
 (`!f:real^M->real^N s.
      closed s /\ f continuous_on s /\
      (!e. bounded {x | x IN s /\ norm(f x) <= e})
      ==> closed(IMAGE f s)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[CLOSED_INTERS_COMPACT] THEN
  REWRITE_TAC[SET_RULE
   `cball(vec 0,e) INTER IMAGE (f:real^M->real^N) s =
    IMAGE f (s INTER {x | x IN s /\ f x IN cball(vec 0,e)})`] THEN
  X_GEN_TAC `e:real` THEN MATCH_MP_TAC COMPACT_CONTINUOUS_IMAGE THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC CONTINUOUS_ON_SUBSET THEN EXISTS_TAC `s:real^M->bool` THEN
    ASM_REWRITE_TAC[] THEN SET_TAC[];
    MATCH_MP_TAC CLOSED_INTER_COMPACT THEN ASM_REWRITE_TAC[] THEN
    REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED] THEN CONJ_TAC THENL
     [ASM_REWRITE_TAC[IN_CBALL_0];
      ASM_SIMP_TAC[CONTINUOUS_CLOSED_PREIMAGE; CLOSED_CBALL]]]);;


let CLOSED_INJECTIVE_IMAGE_SUBSET_SUBSPACE = 
prove
 (`!f:real^M->real^N s t.
        closed s /\ s SUBSET t /\ subspace t /\
        linear f /\
        (!x. x IN t /\ f(x) = vec 0 ==> x = vec 0)
        ==> closed(IMAGE f s)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSED_BOUNDEDPREIM_CONTINUOUS_IMAGE THEN
  ASM_SIMP_TAC[LINEAR_CONTINUOUS_ON] THEN
  MP_TAC(ISPECL [`f:real^M->real^N`; `t:real^M->bool`]
    INJECTIVE_IMP_ISOMETRIC) THEN
  ASM_SIMP_TAC[CLOSED_SUBSPACE; real_ge] THEN
  ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  X_GEN_TAC `e:real` THEN MATCH_MP_TAC BOUNDED_SUBSET THEN
  EXISTS_TAC `cball(vec 0:real^M,e / B)` THEN
  REWRITE_TAC[BOUNDED_CBALL] THEN
  ASM_SIMP_TAC[SUBSET; IN_ELIM_THM; IN_CBALL_0; REAL_LE_RDIV_EQ] THEN
  ASM_MESON_TAC[SUBSET; REAL_LE_TRANS]);;


let BASIS_COORDINATES_LIPSCHITZ = 
prove
 (`!b:real^N->bool.
        independent b
        ==> ?B. &0 < B /\
                !c v. v IN b
                      ==> abs(c v) <= B * norm(vsum b (\v. c(v) % v))`,

  X_GEN_TAC `k:real^N->bool` THEN DISCH_TAC THEN
  FIRST_ASSUM(STRIP_ASSUME_TAC o MATCH_MP INDEPENDENT_BOUND) THEN
  FIRST_ASSUM(X_CHOOSE_THEN `b:num->real^N` STRIP_ASSUME_TAC o
        GEN_REWRITE_RULE I [FINITE_INDEX_NUMSEG]) THEN
  ABBREV_TAC `n = CARD(k:real^N->bool)` THEN
  MP_TAC(ISPECL
   [`(\x. vsum(1..n) (\i. x$i % b i)):real^N->real^N`;
    `span(IMAGE basis (1..n)):real^N->bool`]
        INJECTIVE_IMP_ISOMETRIC) THEN
  REWRITE_TAC[SUBSPACE_SPAN] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [SIMP_TAC[CLOSED_SUBSPACE; SUBSPACE_SPAN]; ALL_TAC] THEN
    CONJ_TAC THENL
     [MATCH_MP_TAC LINEAR_COMPOSE_VSUM THEN
      REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN REPEAT STRIP_TAC THEN
      MATCH_MP_TAC LINEAR_VMUL_COMPONENT THEN
      SIMP_TAC[LINEAR_ID] THEN ASM_ARITH_TAC;
      ALL_TAC] THEN
    X_GEN_TAC `x:real^N` THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [IN_SPAN_IMAGE_BASIS]) THEN
    REWRITE_TAC[IN_NUMSEG] THEN DISCH_TAC THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INJECTIVE_ON_LEFT_INVERSE]) THEN
    DISCH_THEN(X_CHOOSE_TAC `c:real^N->num`) THEN
    SUBGOAL_THEN
     `vsum(1..n) (\i. (x:real^N)$i % b i:real^N) = vsum k (\v. x$(c v) % v)`
    SUBST1_TAC THENL
     [MATCH_MP_TAC VSUM_EQ_GENERAL_INVERSES THEN
      MAP_EVERY EXISTS_TAC [`b:num->real^N`; `c:real^N->num`] THEN
      ASM SET_TAC[];
      ALL_TAC] THEN
    DISCH_TAC THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INDEPENDENT_EXPLICIT]) THEN
    DISCH_THEN(MP_TAC o SPEC `\v:real^N. (x:real^N)$(c v)` o CONJUNCT2) THEN
    ASM_REWRITE_TAC[] THEN ANTS_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
    REWRITE_TAC[CART_EQ; FORALL_IN_IMAGE; VEC_COMPONENT] THEN
    ASM_MESON_TAC[IN_NUMSEG];
    ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `inv(B:real)` THEN ASM_REWRITE_TAC[REAL_LT_INV_EQ] THEN
  ASM_REWRITE_TAC[FORALL_IN_IMAGE; IN_NUMSEG] THEN
  MAP_EVERY X_GEN_TAC [`c:real^N->real`; `j:num`] THEN STRIP_TAC THEN
  ONCE_REWRITE_TAC[REAL_ARITH `inv B * x = x / B`] THEN
  ASM_SIMP_TAC[REAL_LE_RDIV_EQ] THEN
  W(MP_TAC o PART_MATCH (lhs o rand) VSUM_IMAGE o rand o rand o snd) THEN
  ASM_REWRITE_TAC[FINITE_NUMSEG] THEN DISCH_THEN SUBST1_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC
   `(lambda i. if 1 <= i /\ i <= n then c(b i:real^N) else &0):real^N`) THEN
  SIMP_TAC[IN_SPAN_IMAGE_BASIS; LAMBDA_BETA] THEN
  ANTS_TAC THENL [MESON_TAC[IN_NUMSEG]; ALL_TAC] THEN
  MATCH_MP_TAC(REAL_ARITH `x = v /\ u <= y ==> x >= y ==> u <= v`) THEN
  CONJ_TAC THENL
   [AP_TERM_TAC THEN MATCH_MP_TAC VSUM_EQ_NUMSEG THEN
    SUBGOAL_THEN `!i. i <= n ==> i <= dimindex(:N)` MP_TAC THENL
     [ASM_ARITH_TAC; SIMP_TAC[LAMBDA_BETA] THEN DISCH_THEN(K ALL_TAC)] THEN
    REWRITE_TAC[o_THM];
    GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
    ASM_SIMP_TAC[REAL_LE_RMUL_EQ] THEN
    MP_TAC(ISPECL
     [`(lambda i. if 1 <= i /\ i <= n then c(b i:real^N) else &0):real^N`;
      `j:num`] COMPONENT_LE_NORM) THEN
    SUBGOAL_THEN `1 <= j /\ j <= dimindex(:N)` MP_TAC THENL
     [ASM_ARITH_TAC; SIMP_TAC[LAMBDA_BETA] THEN ASM_REWRITE_TAC[]]]);;


let BASIS_COORDINATES_CONTINUOUS = 
prove
 (`!b:real^N->bool e.
        independent b /\ &0 < e
        ==> ?d. &0 < d /\
                !c. norm(vsum b (\v. c(v) % v)) < d
                    ==> !v. v IN b ==> abs(c v) < e`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o MATCH_MP BASIS_COORDINATES_LIPSCHITZ) THEN
  DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `e / B:real` THEN ASM_SIMP_TAC[REAL_LT_DIV] THEN
  X_GEN_TAC `c:real^N->real` THEN DISCH_TAC THEN
  X_GEN_TAC `v:real^N` THEN DISCH_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `B * norm(vsum b (\v:real^N. c v % v))` THEN
  ASM_SIMP_TAC[] THEN ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ]);;

(* ------------------------------------------------------------------------- *)
(* Affine transformations of intervals.                                      *)
(* ------------------------------------------------------------------------- *)


let AFFINITY_INVERSES = 
prove
 (`!m c. ~(m = &0)
         ==> (\x. m % x + c) o (\x. inv(m) % x + (--(inv(m) % c))) = I /\
             (\x. inv(m) % x + (--(inv(m) % c))) o (\x. m % x + c) = I`,

  REWRITE_TAC[FUN_EQ_THM; o_THM; I_THM] THEN
  REWRITE_TAC[VECTOR_ADD_LDISTRIB; VECTOR_MUL_RNEG] THEN
  SIMP_TAC[VECTOR_MUL_ASSOC; REAL_MUL_LINV; REAL_MUL_RINV] THEN
  REPEAT STRIP_TAC THEN VECTOR_ARITH_TAC);;


let REAL_AFFINITY_LE = 
prove
 (`!m c x y. &0 < m ==> (m * x + c <= y <=> x <= inv(m) * y + --(c / m))`,

  REWRITE_TAC[REAL_ARITH `m * x + c <= y <=> x * m <= y - c`] THEN
  SIMP_TAC[GSYM REAL_LE_RDIV_EQ] THEN REAL_ARITH_TAC);;


let REAL_LE_AFFINITY = 
prove
 (`!m c x y. &0 < m ==> (y <= m * x + c <=> inv(m) * y + --(c / m) <= x)`,

  REWRITE_TAC[REAL_ARITH `y <= m * x + c <=> y - c <= x * m`] THEN
  SIMP_TAC[GSYM REAL_LE_LDIV_EQ] THEN REAL_ARITH_TAC);;


let REAL_AFFINITY_LT = 
prove
 (`!m c x y. &0 < m ==> (m * x + c < y <=> x < inv(m) * y + --(c / m))`,

  SIMP_TAC[REAL_LE_AFFINITY; GSYM REAL_NOT_LE]);;


let REAL_LT_AFFINITY = 
prove
 (`!m c x y. &0 < m ==> (y < m * x + c <=> inv(m) * y + --(c / m) < x)`,

  SIMP_TAC[REAL_AFFINITY_LE; GSYM REAL_NOT_LE]);;


let REAL_AFFINITY_EQ = 
prove
 (`!m c x y. ~(m = &0) ==> (m * x + c = y <=> x = inv(m) * y + --(c / m))`,

  CONV_TAC REAL_FIELD);;


let REAL_EQ_AFFINITY = 
prove
 (`!m c x y. ~(m = &0) ==> (y = m * x + c  <=> inv(m) * y + --(c / m) = x)`,

  CONV_TAC REAL_FIELD);;


let VECTOR_AFFINITY_EQ = 
prove
 (`!m c x y. ~(m = &0)
             ==> (m % x + c = y <=> x = inv(m) % y + --(inv(m) % c))`,


let VECTOR_EQ_AFFINITY = 
prove
 (`!m c x y. ~(m = &0)
             ==> (y = m % x + c <=> inv(m) % y + --(inv(m) % c) = x)`,


let IMAGE_AFFINITY_INTERVAL = 
prove
 (`!a b:real^N m c.
        IMAGE (\x. m % x + c) (interval[a,b]) =
            if interval[a,b] = {} then {}
            else if &0 <= m then interval[m % a + c,m % b + c]
            else interval[m % b + c,m % a + c]`,

  REPEAT GEN_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[IMAGE_CLAUSES] THEN
  ASM_CASES_TAC `m = &0` THEN ASM_REWRITE_TAC[REAL_LE_LT] THENL
   [ASM_REWRITE_TAC[VECTOR_MUL_LZERO; VECTOR_ADD_LID; COND_ID] THEN
    REWRITE_TAC[INTERVAL_SING] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  FIRST_ASSUM(DISJ_CASES_TAC o MATCH_MP (REAL_ARITH
   `~(x = &0) ==> &0 < x \/ &0 < --x`)) THEN
  ASM_SIMP_TAC[EXTENSION; IN_IMAGE; REAL_ARITH `&0 < --x ==> ~(&0 < x)`] THENL
   [ALL_TAC;
    ONCE_REWRITE_TAC[VECTOR_ARITH `x = m % y + c <=> c = (--m) % y + x`]] THEN
  ASM_SIMP_TAC[VECTOR_EQ_AFFINITY; REAL_LT_IMP_NZ; UNWIND_THM1] THEN
  SIMP_TAC[IN_INTERVAL; VECTOR_ADD_COMPONENT; VECTOR_MUL_COMPONENT;
           VECTOR_NEG_COMPONENT] THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM REAL_LT_INV_EQ]) THEN
  SIMP_TAC[REAL_AFFINITY_LE; REAL_LE_AFFINITY; real_div] THEN
  DISCH_THEN(K ALL_TAC) THEN REWRITE_TAC[REAL_INV_INV] THEN
  REWRITE_TAC[REAL_MUL_LNEG; REAL_NEGNEG] THEN
  ASM_SIMP_TAC[REAL_FIELD `&0 < m ==> (inv m * x) * m = x`] THEN
  GEN_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN AP_TERM_TAC THEN REAL_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Existence of eigenvectors. The proof is only in this file because it uses *)
(* a few simple results about continuous functions (at least                 *)
(* CONTINUOUS_ON_LIFT_DOT2, CONTINUOUS_ATTAINS_SUP and CLOSED_SUBSPACE).     *)
(* ------------------------------------------------------------------------- *)


let SELF_ADJOINT_HAS_EIGENVECTOR_IN_SUBSPACE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ adjoint f = f /\
        subspace s /\ ~(s = {vec 0}) /\ (!x. x IN s ==> f x IN s)
        ==> ?v c. v IN s /\ norm(v) = &1 /\ f(v) = c % v`,

  
let lemma = prove
   (`!a b. (!x. a * x <= b * x pow 2) ==> &0 <= b ==> a = &0`,
    REPEAT GEN_TAC THEN DISCH_TAC THEN REWRITE_TAC[REAL_LE_LT] THEN
    ASM_CASES_TAC `b = &0` THEN ASM_REWRITE_TAC[] THENL
     [FIRST_X_ASSUM(fun t -> MP_TAC(SPEC `&1` t) THEN
        MP_TAC(SPEC `-- &1` t)) THEN ASM_REAL_ARITH_TAC;
      DISCH_TAC THEN  FIRST_X_ASSUM(MP_TAC o SPEC `a / &2 / b`) THEN
      ASM_SIMP_TAC[REAL_FIELD
       `&0 < b ==> (b * (a / b) pow 2) = a pow 2 / b`] THEN
      REWRITE_TAC[real_div; REAL_MUL_ASSOC] THEN SIMP_TAC[GSYM real_div] THEN
      ASM_SIMP_TAC[REAL_LE_DIV2_EQ] THEN
      REWRITE_TAC[REAL_LT_SQUARE; REAL_ARITH
        `(a * a) / &2 <= (a / &2) pow 2 <=> ~(&0 < a * a)`]]) in
  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`\x:real^N. (f x) dot x`;
                 `s INTER sphere(vec 0:real^N,&1)`]
        CONTINUOUS_ATTAINS_SUP) THEN
  REWRITE_TAC[EXISTS_IN_GSPEC; FORALL_IN_GSPEC; o_DEF] THEN ANTS_TAC THENL
   [ASM_SIMP_TAC[CONTINUOUS_ON_LIFT_DOT2; LINEAR_CONTINUOUS_ON;
                   CONTINUOUS_ON_ID] THEN
    ASM_SIMP_TAC[COMPACT_SPHERE; CLOSED_INTER_COMPACT; CLOSED_SUBSPACE] THEN
    FIRST_X_ASSUM(MP_TAC o MATCH_MP (SET_RULE
      `~(s = {a}) ==> a IN s ==> ?b. ~(b = a) /\ b IN s`)) THEN
    ASM_SIMP_TAC[SUBSPACE_0; IN_SPHERE_0; GSYM MEMBER_NOT_EMPTY; IN_INTER] THEN
    DISCH_THEN(X_CHOOSE_THEN `x:real^N` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `inv(norm x) % x:real^N` THEN
    ASM_REWRITE_TAC[IN_ELIM_THM; VECTOR_SUB_RZERO; NORM_MUL] THEN
    ASM_SIMP_TAC[SUBSPACE_MUL; REAL_ABS_INV; REAL_ABS_NORM] THEN
    ASM_SIMP_TAC[REAL_MUL_LINV; NORM_EQ_0];
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `v:real^N` THEN
    REWRITE_TAC[IN_INTER; IN_SPHERE_0] THEN STRIP_TAC THEN
    ABBREV_TAC `c = (f:real^N->real^N) v dot v` THEN
    EXISTS_TAC `c:real` THEN ASM_REWRITE_TAC[]] THEN
  ABBREV_TAC `p = \x y:real^N. c * (x dot y) - (f x) dot y` THEN
  SUBGOAL_THEN `!x:real^N. x IN s ==> &0 <= p x x` (LABEL_TAC "POSDEF") THENL
   [X_GEN_TAC `x:real^N` THEN EXPAND_TAC "p" THEN REWRITE_TAC[] THEN
    ASM_CASES_TAC `x:real^N = vec 0` THEN DISCH_TAC THEN
    ASM_REWRITE_TAC[DOT_RZERO; REAL_MUL_RZERO; REAL_SUB_LE; REAL_LE_REFL] THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `inv(norm x) % x:real^N`) THEN
    ASM_SIMP_TAC[SUBSPACE_MUL] THEN
    ASM_SIMP_TAC[LINEAR_CMUL; NORM_MUL; REAL_ABS_INV; DOT_RMUL] THEN
    ASM_SIMP_TAC[REAL_ABS_NORM; REAL_MUL_LINV; NORM_EQ_0; DOT_LMUL] THEN
    ASM_SIMP_TAC[GSYM REAL_LE_LDIV_EQ; DOT_POS_LT] THEN
    REWRITE_TAC[GSYM NORM_POW_2; real_div; REAL_INV_POW] THEN REAL_ARITH_TAC;
    ALL_TAC] THEN
  SUBGOAL_THEN `!y:real^N. y IN s ==> !a. p v y * a <= p y y * a pow 2`
  MP_TAC THENL
   [REPEAT STRIP_TAC THEN
    REMOVE_THEN "POSDEF" (MP_TAC o SPEC `v - (&2 * a) % y:real^N`) THEN
    EXPAND_TAC "p" THEN ASM_SIMP_TAC[SUBSPACE_SUB; SUBSPACE_MUL] THEN
    ASM_SIMP_TAC[LINEAR_SUB; LINEAR_CMUL] THEN
    REWRITE_TAC[DOT_LSUB; DOT_LMUL] THEN
    REWRITE_TAC[DOT_RSUB; DOT_RMUL] THEN
    SUBGOAL_THEN `f y dot (v:real^N) = f v dot y` SUBST1_TAC THENL
     [ASM_MESON_TAC[ADJOINT_CLAUSES; DOT_SYM]; ALL_TAC] THEN
    ASM_REWRITE_TAC[GSYM NORM_POW_2] THEN REWRITE_TAC[NORM_POW_2] THEN
    MATCH_MP_TAC(REAL_ARITH
        `&4 * (z - y) = x ==> &0 <= x ==> y <= z`) THEN
    REWRITE_TAC[DOT_SYM] THEN CONV_TAC REAL_RING;
    DISCH_THEN(MP_TAC o GEN `y:real^N` o DISCH `(y:real^N) IN s` o
      MATCH_MP lemma o C MP (ASSUME `(y:real^N) IN s`) o SPEC `y:real^N`) THEN
    ASM_SIMP_TAC[] THEN EXPAND_TAC "p" THEN
    REWRITE_TAC[GSYM DOT_LMUL; GSYM DOT_LSUB] THEN
    DISCH_THEN(MP_TAC o SPEC `c % v - f v:real^N`) THEN
    ASM_SIMP_TAC[SUBSPACE_MUL; SUBSPACE_SUB; DOT_EQ_0; VECTOR_SUB_EQ]]);;


let SELF_ADJOINT_HAS_EIGENVECTOR = 
prove
 (`!f:real^N->real^N.
        linear f /\ adjoint f = f ==> ?v c. norm(v) = &1 /\ f(v) = c % v`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:real^N->real^N`; `(:real^N)`]
        SELF_ADJOINT_HAS_EIGENVECTOR_IN_SUBSPACE) THEN
  ASM_REWRITE_TAC[SUBSPACE_UNIV; IN_UNIV] THEN DISCH_THEN MATCH_MP_TAC THEN
  MATCH_MP_TAC(SET_RULE `!a. ~(a IN s) ==> ~(UNIV = s)`) THEN
  EXISTS_TAC `vec 1:real^N` THEN
  REWRITE_TAC[IN_SING; VEC_EQ; ARITH_EQ]);;


let SELF_ADJOINT_HAS_EIGENVECTOR_BASIS_OF_SUBSPACE = 
prove
 (`!f:real^N->real^N s.
        linear f /\ adjoint f = f /\
        subspace s /\ (!x. x IN s ==> f x IN s)
        ==> ?b. b SUBSET s /\
                pairwise orthogonal b /\
                (!x. x IN b ==> norm x = &1 /\ ?c. f(x) = c % x) /\
                independent b /\
                span b = s /\
                b HAS_SIZE dim s`,

  
let lemma = prove
   (`!f:real^N->real^N s.
          linear f /\ adjoint f = f /\ subspace s /\ (!x. x IN s ==> f x IN s)
          ==> ?b. b SUBSET s /\ b HAS_SIZE dim s /\
                  pairwise orthogonal b /\
                  (!x. x IN b ==> norm x = &1 /\ ?c. f(x) = c % x)`,
    REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN REWRITE_TAC[IMP_IMP] THEN
    GEN_TAC THEN STRIP_TAC THEN GEN_TAC THEN
    WF_INDUCT_TAC `dim(s:real^N->bool)` THEN STRIP_TAC THEN
    ASM_CASES_TAC `dim(s:real^N->bool) = 0` THENL
     [EXISTS_TAC `{}:real^N->bool` THEN
      ASM_SIMP_TAC[HAS_SIZE_CLAUSES; NOT_IN_EMPTY;
                   PAIRWISE_EMPTY; EMPTY_SUBSET];
      ALL_TAC] THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [DIM_EQ_0]) THEN
    DISCH_THEN(ASSUME_TAC o MATCH_MP (SET_RULE
     `~(s SUBSET {a}) ==> ~(s = {a})`)) THEN
    MP_TAC(ISPECL [`f:real^N->real^N`; `s:real^N->bool`]
      SELF_ADJOINT_HAS_EIGENVECTOR_IN_SUBSPACE) THEN
    ASM_REWRITE_TAC[RIGHT_EXISTS_AND_THM] THEN
    DISCH_THEN(X_CHOOSE_THEN `v:real^N` MP_TAC) THEN
    ASM_CASES_TAC `v:real^N = vec 0` THEN ASM_REWRITE_TAC[NORM_0] THEN
    CONV_TAC REAL_RAT_REDUCE_CONV THEN
    DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `{y:real^N | y IN s /\ orthogonal v y}`) THEN
    REWRITE_TAC[SUBSPACE_ORTHOGONAL_TO_VECTOR; IN_ELIM_THM] THEN
    MP_TAC(ISPECL [`span {v:real^N}`; `s:real^N->bool`]
          DIM_SUBSPACE_ORTHOGONAL_TO_VECTORS) THEN
    REWRITE_TAC[ONCE_REWRITE_RULE[ORTHOGONAL_SYM] ORTHOGONAL_TO_SPAN_EQ] THEN
    ASM_REWRITE_TAC[SUBSPACE_SPAN; IN_SING; FORALL_UNWIND_THM2] THEN
    ANTS_TAC THENL
     [MATCH_MP_TAC SPAN_SUBSET_SUBSPACE THEN ASM SET_TAC[];
      DISCH_THEN(SUBST1_TAC o SYM)] THEN
    ASM_REWRITE_TAC[DIM_SPAN; DIM_SING; ARITH_RULE `n < n + 1`] THEN
    ANTS_TAC THENL
     [REWRITE_TAC[SET_RULE `{x | x IN s /\ P x} = s INTER {x | P x}`] THEN
      ASM_SIMP_TAC[SUBSPACE_INTER; SUBSPACE_ORTHOGONAL_TO_VECTOR] THEN
      REWRITE_TAC[orthogonal] THEN X_GEN_TAC `x:real^N` THEN STRIP_TAC THEN
      MATCH_MP_TAC EQ_TRANS THEN
      EXISTS_TAC `(f:real^N->real^N) v dot x` THEN CONJ_TAC THENL
       [ASM_MESON_TAC[ADJOINT_CLAUSES];
        ASM_MESON_TAC[DOT_LMUL; REAL_MUL_RZERO]];
      DISCH_THEN(X_CHOOSE_THEN `b:real^N->bool` STRIP_ASSUME_TAC) THEN
      EXISTS_TAC `(v:real^N) INSERT b` THEN
      ASM_REWRITE_TAC[FORALL_IN_INSERT] THEN
      CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      ASM_REWRITE_TAC[PAIRWISE_INSERT] THEN
      RULE_ASSUM_TAC(REWRITE_RULE[HAS_SIZE; SUBSET; IN_ELIM_THM]) THEN
      CONJ_TAC THENL
       [ASM_SIMP_TAC[HAS_SIZE; FINITE_INSERT; CARD_CLAUSES] THEN
        COND_CASES_TAC THEN ASM_REWRITE_TAC[ADD1] THEN
        ASM_MESON_TAC[ORTHOGONAL_REFL];
        RULE_ASSUM_TAC(REWRITE_RULE[SUBSET; IN_ELIM_THM]) THEN
        ASM_MESON_TAC[ORTHOGONAL_SYM]]]) in
  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:real^N->real^N`; `s:real^N->bool`] lemma) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN
  X_GEN_TAC `b:real^N->bool` THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
   [MATCH_MP_TAC PAIRWISE_ORTHOGONAL_INDEPENDENT THEN
    ASM_MESON_TAC[NORM_ARITH `~(norm(vec 0:real^N) = &1)`];
    DISCH_TAC THEN MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL
     [ASM_MESON_TAC[SPAN_SUBSET_SUBSPACE];
      MATCH_MP_TAC CARD_GE_DIM_INDEPENDENT THEN
      RULE_ASSUM_TAC(REWRITE_RULE[HAS_SIZE]) THEN
      ASM_REWRITE_TAC[LE_REFL]]]);;


let SELF_ADJOINT_HAS_EIGENVECTOR_BASIS = 
prove
 (`!f:real^N->real^N.
        linear f /\ adjoint f = f
        ==> ?b. pairwise orthogonal b /\
                (!x. x IN b ==> norm x = &1 /\ ?c. f(x) = c % x) /\
                independent b /\
                span b = (:real^N) /\
                b HAS_SIZE (dimindex(:N))`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:real^N->real^N`; `(:real^N)`]
        SELF_ADJOINT_HAS_EIGENVECTOR_BASIS_OF_SUBSPACE) THEN
  ASM_REWRITE_TAC[SUBSPACE_UNIV; IN_UNIV; DIM_UNIV; SUBSET_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Diagonalization of symmetric matrix.                                      *)
(* ------------------------------------------------------------------------- *)


let SYMMETRIC_MATRIX_DIAGONALIZABLE_EXPLICIT = 
prove
 (`!A:real^N^N.
    transp A = A
    ==> ?P d. orthogonal_matrix P /\
              transp P ** A ** P = (lambda i j. if i = j then d i else &0)`,

  
let lemma1 = prove
   (`!A:real^N^N P:real^N^N d.
       A ** P = P ** (lambda i j. if i = j then d i else &0) <=>
       !i. 1 <= i /\ i <= dimindex(:N)
           ==> A ** column i P = d i % column i P`,
    SIMP_TAC[CART_EQ; matrix_mul; matrix_vector_mul; LAMBDA_BETA;
             column; VECTOR_MUL_COMPONENT] THEN
    REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[COND_RAND] THEN
    SIMP_TAC[REAL_MUL_RZERO; SUM_DELTA; IN_NUMSEG] THEN
    EQ_TAC THEN STRIP_TAC THEN ASM_SIMP_TAC[] THEN
    REWRITE_TAC[REAL_MUL_SYM]) in
  let lemma2 = prove
   (`!A:real^N^N P:real^N^N d.
          orthogonal_matrix P /\
          transp P ** A ** P = (lambda i j. if i = j then d i else &0) <=>
          orthogonal_matrix P /\
          !i. 1 <= i /\ i <= dimindex(:N)
              ==> A ** column i P = d i % column i P`,
    REPEAT GEN_TAC THEN REWRITE_TAC[GSYM lemma1; orthogonal_matrix] THEN
    ABBREV_TAC `D:real^N^N = lambda i j. if i = j then d i else &0` THEN
    MESON_TAC[MATRIX_MUL_ASSOC; MATRIX_MUL_LID]) in
  REPEAT STRIP_TAC THEN
  REWRITE_TAC[lemma2] THEN REWRITE_TAC[RIGHT_EXISTS_AND_THM] THEN
  REWRITE_TAC[GSYM SKOLEM_THM] THEN
  MP_TAC(ISPEC `\x:real^N. (A:real^N^N) ** x`
    SELF_ADJOINT_HAS_EIGENVECTOR_BASIS) THEN
  ASM_SIMP_TAC[MATRIX_SELF_ADJOINT; MATRIX_VECTOR_MUL_LINEAR;
               MATRIX_OF_MATRIX_VECTOR_MUL] THEN
  DISCH_THEN(X_CHOOSE_THEN `b:real^N->bool` MP_TAC) THEN
  REWRITE_TAC[CONJ_ASSOC] THEN ONCE_REWRITE_TAC[IMP_CONJ_ALT] THEN
  REWRITE_TAC[HAS_SIZE] THEN STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [FINITE_INDEX_NUMSEG]) THEN
  ASM_REWRITE_TAC[IN_NUMSEG; TAUT
   `p /\ q /\ x = y ==> a = b <=> p /\ q /\ ~(a = b) ==> ~(x = y)`] THEN
  DISCH_THEN(X_CHOOSE_THEN `f:num->real^N` STRIP_ASSUME_TAC) THEN
  ASM_REWRITE_TAC[PAIRWISE_IMAGE; FORALL_IN_IMAGE] THEN
  ASM_SIMP_TAC[pairwise; IN_NUMSEG] THEN STRIP_TAC THEN
  EXISTS_TAC `transp(lambda i. f i):real^N^N` THEN
  SIMP_TAC[COLUMN_TRANSP; ORTHOGONAL_MATRIX_TRANSP] THEN
  SIMP_TAC[ORTHOGONAL_MATRIX_ORTHONORMAL_ROWS_INDEXED; row] THEN
  SIMP_TAC[LAMBDA_ETA; LAMBDA_BETA; pairwise; IN_NUMSEG] THEN
  ASM_MESON_TAC[]);;


let SYMMETRIC_MATRIX_IMP_DIAGONALIZABLE = 
prove
 (`!A:real^N^N.
     transp A = A
     ==> ?P. orthogonal_matrix P /\ diagonal_matrix(transp P ** A ** P)`,

  GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP SYMMETRIC_MATRIX_DIAGONALIZABLE_EXPLICIT) THEN
  MATCH_MP_TAC MONO_EXISTS THEN REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  SIMP_TAC[diagonal_matrix; LAMBDA_BETA]);;


let SYMMETRIC_MATRIX_EQ_DIAGONALIZABLE = 
prove
 (`!A:real^N^N.
     transp A = A <=>
     ?P. orthogonal_matrix P /\ diagonal_matrix(transp P ** A ** P)`,

  GEN_TAC THEN EQ_TAC THEN
  REWRITE_TAC[SYMMETRIC_MATRIX_IMP_DIAGONALIZABLE] THEN
  REWRITE_TAC[orthogonal_matrix] THEN
  DISCH_THEN(X_CHOOSE_THEN `P:real^N^N` STRIP_ASSUME_TAC) THEN
  ABBREV_TAC `D:real^N^N = transp P ** (A:real^N^N) ** P` THEN
  SUBGOAL_THEN `A:real^N^N = P ** (D:real^N^N) ** transp P` SUBST1_TAC THENL
   [EXPAND_TAC "D" THEN REWRITE_TAC[MATRIX_MUL_ASSOC] THEN
    ASM_REWRITE_TAC[MATRIX_MUL_LID] THEN
    ASM_REWRITE_TAC[GSYM MATRIX_MUL_ASSOC; MATRIX_MUL_RID];
    REWRITE_TAC[MATRIX_TRANSP_MUL; TRANSP_TRANSP; MATRIX_MUL_ASSOC] THEN
    ASM_MESON_TAC[TRANSP_DIAGONAL_MATRIX]]);;

(* ------------------------------------------------------------------------- *)
(* Some matrix identities are easier to deduce for invertible matrices. We   *)
(* can then extend by continuity, which is why this material needs to be     *)
(* here after basic topological notions have been defined.                   *)
(* ------------------------------------------------------------------------- *)


let CONTINUOUS_LIFT_DET = 
prove
 (`!(A:A->real^N^N) net.
        (!i j. 1 <= i /\ i <= dimindex(:N) /\
               1 <= j /\ j <= dimindex(:N)
               ==> (\x. lift(A x$i$j)) continuous net)
        ==> (\x. lift(det(A x))) continuous net`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[det] THEN
  SIMP_TAC[LIFT_SUM; FINITE_PERMUTATIONS; FINITE_NUMSEG; o_DEF] THEN
  MATCH_MP_TAC CONTINUOUS_VSUM THEN
  SIMP_TAC[FINITE_PERMUTATIONS; FINITE_NUMSEG; LIFT_CMUL; IN_ELIM_THM] THEN
  X_GEN_TAC `p:num->num` THEN DISCH_TAC THEN
  MATCH_MP_TAC CONTINUOUS_CMUL THEN
  MATCH_MP_TAC CONTINUOUS_LIFT_PRODUCT THEN
  REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN
  REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP PERMUTES_IMAGE) THEN
  DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE `s = t ==> s SUBSET t`)) THEN
  ASM_SIMP_TAC[SUBSET; FORALL_IN_IMAGE; IN_NUMSEG]);;


let CONTINUOUS_ON_LIFT_DET = 
prove
 (`!A:real^M->real^N^N s.
        (!i j. 1 <= i /\ i <= dimindex(:N) /\
               1 <= j /\ j <= dimindex(:N)
               ==> (\x. lift(A x$i$j)) continuous_on s)
        ==> (\x. lift(det(A x))) continuous_on s`,


let NEARBY_INVERTIBLE_MATRIX = 
prove
 (`!A:real^N^N.
     ?e. &0 < e /\ !x. ~(x = &0) /\ abs x < e ==> invertible(A + x %% mat 1)`,

  GEN_TAC THEN MP_TAC(ISPEC `A:real^N^N` CHARACTERISTIC_POLYNOMIAL) THEN
  DISCH_THEN(X_CHOOSE_THEN `a:num->real` STRIP_ASSUME_TAC) THEN
  MP_TAC(ISPECL [`dimindex(:N)`; `a:num->real`] REAL_POLYFUN_FINITE_ROOTS) THEN
  MATCH_MP_TAC(TAUT `q /\ (p ==> r) ==> (p <=> q) ==> r`) THEN CONJ_TAC THENL
   [EXISTS_TAC `dimindex(:N)` THEN ASM_REWRITE_TAC[IN_NUMSEG] THEN ARITH_TAC;
    ALL_TAC] THEN
  DISCH_THEN(MP_TAC o ISPEC `lift` o MATCH_MP FINITE_IMAGE) THEN
  DISCH_THEN(MP_TAC o MATCH_MP LIMIT_POINT_FINITE) THEN
  DISCH_THEN(MP_TAC o SPEC `lift(&0)`) THEN
  REWRITE_TAC[LIMPT_APPROACHABLE; EXISTS_IN_IMAGE; EXISTS_IN_GSPEC] THEN
  REWRITE_TAC[DIST_LIFT; LIFT_EQ; REAL_SUB_RZERO; NOT_FORALL_THM; NOT_IMP] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[NOT_EXISTS_THM] THEN
  DISCH_THEN(fun th -> X_GEN_TAC `x:real` THEN STRIP_TAC THEN
                MP_TAC(SPEC `--x:real` th)) THEN
  FIRST_X_ASSUM(SUBST1_TAC o SYM o SPEC `--x:real`) THEN
  ASM_REWRITE_TAC[REAL_NEG_EQ_0; REAL_ABS_NEG] THEN
  ONCE_REWRITE_TAC[GSYM INVERTIBLE_NEG] THEN
  REWRITE_TAC[INVERTIBLE_DET_NZ; CONTRAPOS_THM] THEN
  REWRITE_TAC[MATRIX_SUB; MATRIX_NEG_MINUS1] THEN
  ONCE_REWRITE_TAC[REAL_ARITH `--x = -- &1 * x`] THEN
  REWRITE_TAC[GSYM MATRIX_CMUL_ADD_LDISTRIB; GSYM MATRIX_CMUL_ASSOC] THEN
  REWRITE_TAC[MATRIX_CMUL_LID; MATRIX_ADD_SYM]);;


let MATRIX_WLOG_INVERTIBLE = 
prove
 (`!P. (!A:real^N^N. invertible A ==> P A) /\
       (!A:real^N^N. ?d. &0 < d /\
                         closed {x | x IN cball(vec 0,d) /\
                                     P(A + drop x %% mat 1)})
       ==> !A:real^N^N. P A`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_ASSUM(MP_TAC o SPEC `vec 0:real^1` o
    GEN_REWRITE_RULE I [CLOSED_LIMPT]) THEN
  ASM_SIMP_TAC[IN_ELIM_THM; DROP_VEC; MATRIX_CMUL_LZERO; MATRIX_ADD_RID] THEN
  ANTS_TAC THENL [ALL_TAC; CONV_TAC TAUT] THEN
  MP_TAC(ISPEC `A:real^N^N` NEARBY_INVERTIBLE_MATRIX) THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[LIMPT_APPROACHABLE] THEN X_GEN_TAC `k:real` THEN
  DISCH_TAC THEN REWRITE_TAC[EXISTS_LIFT; IN_ELIM_THM] THEN
  REWRITE_TAC[GSYM LIFT_NUM; IN_CBALL_0; NORM_LIFT; DIST_LIFT] THEN
  REWRITE_TAC[REAL_SUB_RZERO; LIFT_EQ; LIFT_DROP] THEN
  EXISTS_TAC `min d ((min e k) / &2)` THEN
  CONJ_TAC THENL [ALL_TAC; ASM_REAL_ARITH_TAC] THEN
  CONJ_TAC THENL [ASM_REAL_ARITH_TAC; FIRST_X_ASSUM MATCH_MP_TAC] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REAL_ARITH_TAC);;


let SYLVESTER_DETERMINANT_IDENTITY = 
prove
 (`!A:real^N^M B:real^M^N. det(mat 1 + A ** B) = det(mat 1 + B ** A)`,

  
let lemma1 = prove
   (`!A:real^N^N B:real^N^N. det(mat 1 + A ** B) = det(mat 1 + B ** A)`,
    ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN GEN_TAC THEN
    MATCH_MP_TAC MATRIX_WLOG_INVERTIBLE THEN CONJ_TAC THENL
     [REPEAT STRIP_TAC THEN
      SUBGOAL_THEN `det((mat 1 + A ** B) ** A:real^N^N) =
                    det(A ** (mat 1 + B ** A))`
      MP_TAC THENL
       [REWRITE_TAC[MATRIX_ADD_RDISTRIB; MATRIX_ADD_LDISTRIB] THEN
        REWRITE_TAC[MATRIX_MUL_LID; MATRIX_MUL_RID; MATRIX_MUL_ASSOC];
        REWRITE_TAC[DET_MUL] THEN
        FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INVERTIBLE_DET_NZ]) THEN
        CONV_TAC REAL_RING];
      X_GEN_TAC `A:real^N^N` THEN EXISTS_TAC `&1` THEN
      REWRITE_TAC[REAL_LT_01; SET_RULE
       `{x | x IN s /\ P x} = s INTER {x | P x}`] THEN
      MATCH_MP_TAC CLOSED_INTER THEN REWRITE_TAC[CLOSED_CBALL] THEN
      ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN
      REWRITE_TAC[GSYM LIFT_EQ; LIFT_NUM] THEN
      REWRITE_TAC[SET_RULE `{x | f x = a} = {x | f x IN {a}}`] THEN
      MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE_UNIV THEN
      REWRITE_TAC[CLOSED_SING; LIFT_SUB] THEN X_GEN_TAC `x:real^1` THEN
      REWRITE_TAC[o_DEF; LIFT_SUB] THEN MATCH_MP_TAC CONTINUOUS_SUB THEN
      CONJ_TAC THEN MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN
      MAP_EVERY X_GEN_TAC [`i:num`; `j:num`] THEN STRIP_TAC THEN
      ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; LIFT_ADD] THEN
      MATCH_MP_TAC CONTINUOUS_ADD THEN
      ASM_SIMP_TAC[matrix_mul; LAMBDA_BETA; CONTINUOUS_CONST] THEN
      SIMP_TAC[LIFT_SUM; FINITE_NUMSEG; o_DEF] THEN
      MATCH_MP_TAC CONTINUOUS_VSUM THEN
      REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN X_GEN_TAC `k:num` THEN
      DISCH_TAC THENL [ONCE_REWRITE_TAC[REAL_MUL_SYM]; ALL_TAC] THEN
      REWRITE_TAC[LIFT_CMUL] THEN MATCH_MP_TAC CONTINUOUS_CMUL THEN
      REWRITE_TAC[MATRIX_ADD_COMPONENT; MATRIX_CMUL_COMPONENT; LIFT_ADD] THEN
      MATCH_MP_TAC CONTINUOUS_ADD THEN REWRITE_TAC[CONTINUOUS_CONST] THEN
      REWRITE_TAC[ONCE_REWRITE_RULE[REAL_MUL_SYM] LIFT_CMUL] THEN
      MATCH_MP_TAC CONTINUOUS_CMUL THEN
      REWRITE_TAC[LIFT_DROP; CONTINUOUS_AT_ID]]) in
  let lemma2 = prove
   (`!A:real^N^M B:real^M^N.
          dimindex(:M) <= dimindex(:N)
          ==> det(mat 1 + A ** B) = det(mat 1 + B ** A)`,
    REPEAT STRIP_TAC THEN
    MAP_EVERY ABBREV_TAC
     [`A':real^N^N =
          lambda i j. if i <= dimindex(:M) then (A:real^N^M)$i$j
                      else &0`;
      `B':real^N^N =
          lambda i j. if j <= dimindex(:M) then (B:real^M^N)$i$j
                      else &0`] THEN
    MP_TAC(ISPECL [`A':real^N^N`; `B':real^N^N`] lemma1) THEN
    SUBGOAL_THEN
     `(B':real^N^N) ** (A':real^N^N) = (B:real^M^N) ** (A:real^N^M)`
    SUBST1_TAC THENL
     [MAP_EVERY EXPAND_TAC ["A'";
 "B'"] THEN
      SIMP_TAC[CART_EQ; LAMBDA_BETA; matrix_mul] THEN REPEAT STRIP_TAC THEN
      MATCH_MP_TAC SUM_EQ_SUPERSET THEN
      ASM_SIMP_TAC[IN_NUMSEG; REAL_MUL_LZERO; FINITE_NUMSEG; SUBSET_NUMSEG;
                   LE_REFL; TAUT `(p /\ q) /\ ~(p /\ r) <=> p /\ q /\ ~r`];
      DISCH_THEN(SUBST1_TAC o SYM)] THEN
    REWRITE_TAC[det] THEN MATCH_MP_TAC EQ_TRANS THEN EXISTS_TAC
     `sum {p | p permutes 1..dimindex(:N) /\ !i. dimindex(:M) < i ==> p i = i}
          (\p. sign p * product (1..dimindex(:N))
                     (\i. (mat 1 + (A':real^N^N) ** (B':real^N^N))$i$p i))` THEN
    CONJ_TAC THENL
     [ALL_TAC;
      CONV_TAC SYM_CONV THEN MATCH_MP_TAC SUM_SUPERSET THEN
      CONJ_TAC THENL [SET_TAC[]; SIMP_TAC[IN_ELIM_THM; IMP_CONJ]] THEN
      X_GEN_TAC `p:num->num` THEN REPEAT STRIP_TAC THEN
      REWRITE_TAC[REAL_ENTIRE; PRODUCT_EQ_0_NUMSEG] THEN DISJ2_TAC THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [NOT_FORALL_THM]) THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `k:num` THEN
      REWRITE_TAC[NOT_IMP] THEN STRIP_TAC THEN
      FIRST_ASSUM(MP_TAC o SPEC `k:num` o CONJUNCT1 o
        GEN_REWRITE_RULE I [permutes]) THEN
      ASM_REWRITE_TAC[IN_NUMSEG] THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
      FIRST_ASSUM(MP_TAC o MATCH_MP PERMUTES_IMAGE) THEN
      DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE `s = t ==> s SUBSET t`)) THEN
      ASM_SIMP_TAC[SUBSET; FORALL_IN_IMAGE; IN_NUMSEG] THEN
      DISCH_THEN(MP_TAC o SPEC `k:num`) THEN ASM_SIMP_TAC[] THEN STRIP_TAC THEN
      ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MAT_COMPONENT; REAL_ADD_LID] THEN
      ASM_SIMP_TAC[matrix_mul; LAMBDA_BETA] THEN
      MATCH_MP_TAC SUM_EQ_0_NUMSEG THEN REPEAT STRIP_TAC THEN
      REWRITE_TAC[REAL_ENTIRE] THEN DISJ1_TAC THEN EXPAND_TAC "A'" THEN
      ASM_SIMP_TAC[LAMBDA_BETA; GSYM NOT_LT]] THEN
    CONV_TAC SYM_CONV THEN MATCH_MP_TAC SUM_EQ_GENERAL THEN
    EXISTS_TAC `\f:num->num. f` THEN REWRITE_TAC[IN_ELIM_THM] THEN
    CONJ_TAC THEN X_GEN_TAC `p:num->num` THEN STRIP_TAC THENL
     [REWRITE_TAC[MESON[] `(?!x. P x /\ x = y) <=> P y`] THEN CONJ_TAC THENL
       [MATCH_MP_TAC PERMUTES_SUBSET THEN
        EXISTS_TAC `1..dimindex(:M)` THEN
        ASM_REWRITE_TAC[SUBSET_NUMSEG; LE_REFL];
        X_GEN_TAC `k:num` THEN DISCH_TAC THEN
        FIRST_X_ASSUM(MATCH_MP_TAC o CONJUNCT1 o
          GEN_REWRITE_RULE I [permutes]) THEN
        ASM_REWRITE_TAC[IN_NUMSEG; DE_MORGAN_THM; NOT_LE]];
      MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
       [MATCH_MP_TAC PERMUTES_SUPERSET THEN
        EXISTS_TAC `1..dimindex(:N)` THEN
        ASM_REWRITE_TAC[IN_DIFF; IN_NUMSEG] THEN ASM_MESON_TAC[NOT_LE];
        DISCH_TAC] THEN
      AP_TERM_TAC THEN FIRST_ASSUM(SUBST1_TAC o MATCH_MP (ARITH_RULE
       `m:num <= n ==> n = m + (n - m)`)) THEN
      SIMP_TAC[PRODUCT_ADD_SPLIT; ARITH_RULE `1 <= n + 1`] THEN
      MATCH_MP_TAC(REAL_RING `x = y /\ z = &1 ==> x = y * z`) THEN
      CONJ_TAC THENL
       [MATCH_MP_TAC PRODUCT_EQ_NUMSEG THEN
        X_GEN_TAC `i:num` THEN STRIP_TAC THEN
        SUBGOAL_THEN `i <= dimindex(:N)` ASSUME_TAC THENL
         [ASM_ARITH_TAC; ALL_TAC] THEN
        MP_TAC(ISPECL [`p:num->num`; `1..dimindex(:M)`] PERMUTES_IMAGE) THEN
        ASM_REWRITE_TAC[] THEN
        DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE `s = t ==> s SUBSET t`)) THEN
        ASM_SIMP_TAC[SUBSET; FORALL_IN_IMAGE; IN_NUMSEG] THEN
        DISCH_THEN(MP_TAC o SPEC `i:num`) THEN
        ASM_REWRITE_TAC[] THEN STRIP_TAC THEN
        SUBGOAL_THEN `(p:num->num) i <= dimindex(:N)` ASSUME_TAC THENL
         [ASM_ARITH_TAC; ALL_TAC] THEN
        ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MAT_COMPONENT] THEN
        AP_TERM_TAC THEN ASM_SIMP_TAC[matrix_mul; LAMBDA_BETA] THEN
        MATCH_MP_TAC SUM_EQ_NUMSEG THEN REPEAT STRIP_TAC THEN
        MAP_EVERY EXPAND_TAC ["A'"; "B'"] THEN
        ASM_SIMP_TAC[LAMBDA_BETA];
        MATCH_MP_TAC PRODUCT_EQ_1_NUMSEG THEN
        ASM_SIMP_TAC[ARITH_RULE `n + 1 <= i ==> n < i`] THEN
        ASM_SIMP_TAC[ARITH_RULE `m:num <= n ==> m + (n - m) = n`] THEN
        X_GEN_TAC `i:num` THEN STRIP_TAC THEN
        SUBGOAL_THEN `1 <= i` ASSUME_TAC THENL [ASM_ARITH_TAC; ALL_TAC] THEN
        ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MAT_COMPONENT] THEN
        ASM_SIMP_TAC[REAL_EQ_ADD_LCANCEL_0; matrix_mul; LAMBDA_BETA] THEN
        MATCH_MP_TAC SUM_EQ_0_NUMSEG THEN REPEAT STRIP_TAC THEN
        REWRITE_TAC[REAL_ENTIRE] THEN DISJ1_TAC THEN EXPAND_TAC "A'" THEN
        ASM_SIMP_TAC[LAMBDA_BETA; ARITH_RULE `m + 1 <= i ==> ~(i <= m)`]]]) in
  REPEAT GEN_TAC THEN DISJ_CASES_TAC (ARITH_RULE
   `dimindex(:M) <= dimindex(:N) \/ dimindex(:N) <= dimindex(:M)`)
  THENL [ALL_TAC; CONV_TAC SYM_CONV] THEN
  MATCH_MP_TAC lemma2 THEN ASM_REWRITE_TAC[]);;


let COFACTOR_MATRIX_MUL = 
prove
 (`!A B:real^N^N. cofactor(A ** B) = cofactor(A) ** cofactor(B)`,

  MATCH_MP_TAC MATRIX_WLOG_INVERTIBLE THEN CONJ_TAC THENL
   [GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC MATRIX_WLOG_INVERTIBLE THEN
    CONJ_TAC THENL
     [ASM_SIMP_TAC[COFACTOR_MATRIX_INV; GSYM INVERTIBLE_DET_NZ;
                   INVERTIBLE_MATRIX_MUL] THEN
      REWRITE_TAC[DET_MUL; MATRIX_MUL_LMUL] THEN
      REWRITE_TAC[MATRIX_MUL_RMUL; MATRIX_CMUL_ASSOC;
                  GSYM MATRIX_TRANSP_MUL] THEN
      ASM_SIMP_TAC[MATRIX_INV_MUL];
      GEN_TAC THEN EXISTS_TAC `&1` THEN REWRITE_TAC[REAL_LT_01]];
    X_GEN_TAC `A:real^N^N` THEN EXISTS_TAC `&1` THEN
    REWRITE_TAC[REAL_LT_01] THEN REWRITE_TAC[RIGHT_AND_FORALL_THM] THEN
    MATCH_MP_TAC CLOSED_FORALL THEN GEN_TAC] THEN
  REWRITE_TAC[SET_RULE
   `{x | x IN s /\ P x} = s INTER {x | P x}`] THEN
  MATCH_MP_TAC CLOSED_INTER THEN REWRITE_TAC[CLOSED_CBALL] THEN
  REWRITE_TAC[CART_EQ] THEN
  MATCH_MP_TAC CLOSED_FORALL_IN THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
  MATCH_MP_TAC CLOSED_FORALL_IN THEN X_GEN_TAC `j:num` THEN STRIP_TAC THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN
  REWRITE_TAC[GSYM LIFT_EQ; LIFT_NUM] THEN
  REWRITE_TAC[SET_RULE `{x | f x = a} = {x | f x IN {a}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE_UNIV THEN
  REWRITE_TAC[CLOSED_SING; LIFT_SUB] THEN X_GEN_TAC `x:real^1` THEN
  ASM_SIMP_TAC[matrix_mul; LAMBDA_BETA; cofactor; LIFT_SUM;
               FINITE_NUMSEG; o_DEF] THEN
  (MATCH_MP_TAC CONTINUOUS_SUB THEN CONJ_TAC THENL
    [ALL_TAC;
     MATCH_MP_TAC CONTINUOUS_VSUM THEN
     REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN
     X_GEN_TAC `k:num` THEN STRIP_TAC THEN
     REWRITE_TAC[LIFT_CMUL] THEN MATCH_MP_TAC CONTINUOUS_MUL THEN
     REWRITE_TAC[o_DEF] THEN CONJ_TAC]) THEN
  MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN STRIP_TAC THEN
  ASM_SIMP_TAC[LAMBDA_BETA; CONTINUOUS_CONST] THEN
  REPEAT(W(fun (asl,w) ->
   let t = find_term is_cond w in
   ASM_CASES_TAC (lhand(rator t)) THEN ASM_REWRITE_TAC[CONTINUOUS_CONST])) THEN
  SIMP_TAC[LIFT_SUM; FINITE_NUMSEG; o_DEF] THEN
  TRY(MATCH_MP_TAC CONTINUOUS_VSUM THEN REWRITE_TAC[FINITE_NUMSEG] THEN
      REWRITE_TAC[IN_NUMSEG] THEN X_GEN_TAC `p:num` THEN STRIP_TAC) THEN
  REWRITE_TAC[LIFT_CMUL] THEN
  TRY(MATCH_MP_TAC CONTINUOUS_MUL THEN
      REWRITE_TAC[o_DEF; CONTINUOUS_CONST]) THEN
  REWRITE_TAC[MATRIX_ADD_COMPONENT; LIFT_ADD] THEN
  MATCH_MP_TAC CONTINUOUS_ADD THEN REWRITE_TAC[CONTINUOUS_CONST] THEN
  REWRITE_TAC[MATRIX_CMUL_COMPONENT; LIFT_CMUL; o_DEF] THEN
  MATCH_MP_TAC CONTINUOUS_MUL THEN
  REWRITE_TAC[CONTINUOUS_CONST; o_DEF; LIFT_DROP; CONTINUOUS_AT_ID]);;


let DET_COFACTOR = 
prove
 (`!A:real^N^N. det(cofactor A) = det(A) pow (dimindex(:N) - 1)`,

  MATCH_MP_TAC MATRIX_WLOG_INVERTIBLE THEN CONJ_TAC THEN
  X_GEN_TAC `A:real^N^N` THENL
   [REWRITE_TAC[INVERTIBLE_DET_NZ] THEN STRIP_TAC THEN
    FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_FIELD
     `~(a = &0) ==> a * x = a * y ==> x = y`)) THEN
    GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM DET_TRANSP] THEN
    REWRITE_TAC[GSYM DET_MUL; MATRIX_MUL_RIGHT_COFACTOR] THEN
    REWRITE_TAC[DET_CMUL; GSYM(CONJUNCT2 real_pow); DET_I; REAL_MUL_RID] THEN
    SIMP_TAC[DIMINDEX_GE_1; ARITH_RULE `1 <= n ==> SUC(n - 1) = n`];
    ALL_TAC] THEN
  EXISTS_TAC `&1` THEN REWRITE_TAC[REAL_LT_01] THEN
  REWRITE_TAC[SET_RULE
   `{x | x IN s /\ P x} = s INTER {x | P x}`] THEN
  MATCH_MP_TAC CLOSED_INTER THEN REWRITE_TAC[CLOSED_CBALL] THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN
  REWRITE_TAC[GSYM LIFT_EQ; LIFT_NUM] THEN
  REWRITE_TAC[SET_RULE `{x | f x = a} = {x | f x IN {a}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE_UNIV THEN
  REWRITE_TAC[CLOSED_SING; LIFT_SUB] THEN X_GEN_TAC `x:real^1` THEN
  MATCH_MP_TAC CONTINUOUS_SUB THEN
  CONJ_TAC THENL [ALL_TAC; MATCH_MP_TAC CONTINUOUS_LIFT_POW] THEN
  MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN
  MAP_EVERY X_GEN_TAC [`i:num`; `j:num`] THEN STRIP_TAC THEN
  ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MATRIX_CMUL_COMPONENT; LIFT_ADD;
               LIFT_CMUL; LIFT_DROP; CONTINUOUS_ADD; CONTINUOUS_CONST;
               CONTINUOUS_MUL; o_DEF; LIFT_DROP; CONTINUOUS_AT_ID] THEN
  ASM_SIMP_TAC[cofactor; LAMBDA_BETA] THEN
  MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN STRIP_TAC THEN
  ASM_SIMP_TAC[LAMBDA_BETA] THEN
  REPEAT(W(fun (asl,w) ->
   let t = find_term is_cond w in
   ASM_CASES_TAC (lhand(rator t)) THEN ASM_REWRITE_TAC[CONTINUOUS_CONST])) THEN
  ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MATRIX_CMUL_COMPONENT; LIFT_ADD;
               LIFT_CMUL; LIFT_DROP; CONTINUOUS_ADD; CONTINUOUS_CONST;
               CONTINUOUS_MUL; o_DEF; LIFT_DROP; CONTINUOUS_AT_ID]);;


let INVERTIBLE_COFACTOR = 
prove
 (`!A:real^N^N. invertible(cofactor A) <=> dimindex(:N) = 1 \/ invertible A`,

  SIMP_TAC[DET_COFACTOR; INVERTIBLE_DET_NZ; REAL_POW_EQ_0; DE_MORGAN_THM;
           DIMINDEX_GE_1; ARITH_RULE `1 <= n ==> (n - 1 = 0 <=> n = 1)`;
           DISJ_ACI]);;


let COFACTOR_COFACTOR = 
prove
 (`!A:real^N^N.
     2 <= dimindex(:N)
     ==> cofactor(cofactor A) = (det(A) pow (dimindex(:N) - 2)) %% A`,

  REWRITE_TAC[RIGHT_FORALL_IMP_THM] THEN DISCH_TAC THEN
  MATCH_MP_TAC MATRIX_WLOG_INVERTIBLE THEN CONJ_TAC THEN
  X_GEN_TAC `A:real^N^N` THENL
   [REWRITE_TAC[INVERTIBLE_DET_NZ] THEN DISCH_TAC THEN
    MP_TAC(ISPECL [`A:real^N^N`; `transp(cofactor A):real^N^N`]
        COFACTOR_MATRIX_MUL) THEN
    REWRITE_TAC[MATRIX_MUL_RIGHT_COFACTOR; COFACTOR_CMUL; COFACTOR_I] THEN
    REWRITE_TAC[COFACTOR_TRANSP] THEN
    DISCH_THEN(MP_TAC o AP_TERM `transp:real^N^N->real^N^N`) THEN
    REWRITE_TAC[MATRIX_TRANSP_MUL; TRANSP_TRANSP; TRANSP_MATRIX_CMUL] THEN
    REWRITE_TAC[TRANSP_MAT] THEN
    DISCH_THEN(MP_TAC o AP_TERM `(\x. x ** A):real^N^N->real^N^N`) THEN
    REWRITE_TAC[GSYM MATRIX_MUL_ASSOC; MATRIX_MUL_LEFT_COFACTOR] THEN
    REWRITE_TAC[MATRIX_MUL_LMUL; MATRIX_MUL_RMUL] THEN
    REWRITE_TAC[MATRIX_MUL_LID; MATRIX_MUL_RID] THEN
    DISCH_THEN(MP_TAC o AP_TERM `\x:real^N^N. inv(det(A:real^N^N)) %% x`) THEN
    ASM_SIMP_TAC[MATRIX_CMUL_ASSOC; REAL_MUL_LINV; MATRIX_CMUL_LID] THEN
    DISCH_THEN(SUBST1_TAC o SYM) THEN AP_THM_TAC THEN AP_TERM_TAC THEN
    ASM_SIMP_TAC[REAL_POW_SUB; ARITH_RULE `2 <= n ==> 1 <= n`] THEN
    REWRITE_TAC[REAL_POW_2; real_div; REAL_INV_POW] THEN REAL_ARITH_TAC;
    POP_ASSUM(K ALL_TAC)] THEN
  EXISTS_TAC `&1` THEN REWRITE_TAC[REAL_LT_01] THEN
  REWRITE_TAC[SET_RULE
   `{x | x IN s /\ P x} = s INTER {x | P x}`] THEN
  MATCH_MP_TAC CLOSED_INTER THEN REWRITE_TAC[CLOSED_CBALL] THEN
  REWRITE_TAC[CART_EQ] THEN
  MATCH_MP_TAC CLOSED_FORALL_IN THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
  MATCH_MP_TAC CLOSED_FORALL_IN THEN X_GEN_TAC `j:num` THEN STRIP_TAC THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_0] THEN
  REWRITE_TAC[GSYM LIFT_EQ; LIFT_NUM] THEN
  REWRITE_TAC[SET_RULE `{x | f x = a} = {x | f x IN {a}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE_UNIV THEN
  REWRITE_TAC[CLOSED_SING; LIFT_SUB] THEN X_GEN_TAC `x:real^1` THEN
  MATCH_MP_TAC CONTINUOUS_SUB THEN CONJ_TAC THENL
   [REPLICATE_TAC 2
     (ONCE_REWRITE_TAC[cofactor] THEN ASM_SIMP_TAC[LAMBDA_BETA] THEN
      MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN REPEAT STRIP_TAC THEN
      ASM_SIMP_TAC[LAMBDA_BETA] THEN
      REPEAT(W(fun (asl,w) ->
       let t = find_term is_cond w in
       ASM_CASES_TAC (lhand(rator t)) THEN
       ASM_REWRITE_TAC[CONTINUOUS_CONST])));
    REWRITE_TAC[MATRIX_CMUL_COMPONENT; LIFT_CMUL] THEN
    MATCH_MP_TAC CONTINUOUS_MUL THEN REWRITE_TAC[o_DEF] THEN CONJ_TAC THENL
     [MATCH_MP_TAC CONTINUOUS_LIFT_POW THEN
      MATCH_MP_TAC CONTINUOUS_LIFT_DET THEN REPEAT STRIP_TAC;
      ALL_TAC]] THEN
  REWRITE_TAC[MATRIX_ADD_COMPONENT; MATRIX_CMUL_COMPONENT] THEN
  ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  REWRITE_TAC[LIFT_ADD; LIFT_CMUL; LIFT_DROP] THEN
  SIMP_TAC[CONTINUOUS_ADD; CONTINUOUS_CONST; CONTINUOUS_CMUL;
           CONTINUOUS_AT_ID]);;


let RANK_COFACTOR_EQ_FULL = 
prove
 (`!A:real^N^N. rank(cofactor A) = dimindex(:N) <=>
                dimindex(:N) = 1 \/ rank A = dimindex(:N)`,

  REWRITE_TAC[RANK_EQ_FULL_DET; DET_COFACTOR; REAL_POW_EQ_0] THEN
  SIMP_TAC[DIMINDEX_GE_1; ARITH_RULE `1 <= n ==> (n - 1 = 0 <=> n = 1)`] THEN
  CONV_TAC TAUT);;


let COFACTOR_EQ_0 = 
prove
 (`!A:real^N^N. cofactor A = mat 0 <=> rank(A) < dimindex(:N) - 1`,

  
let lemma1 = prove
   (`!A:real^N^N. rank(A) < dimindex(:N) - 1 ==> cofactor A = mat 0`,
    GEN_TAC THEN REWRITE_TAC[RANK_ROW] THEN DISCH_TAC THEN
    SIMP_TAC[CART_EQ; cofactor; MAT_COMPONENT; LAMBDA_BETA; COND_ID] THEN
    X_GEN_TAC `m:num` THEN STRIP_TAC THEN X_GEN_TAC `n:num` THEN STRIP_TAC THEN
    REWRITE_TAC[DET_EQ_0_RANK] THEN FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP
     (ARITH_RULE `r < n - 1 ==> s <= r + 1 ==> s < n`)) THEN
    REWRITE_TAC[RANK_ROW; rows] THEN MATCH_MP_TAC LE_TRANS THEN
    EXISTS_TAC
     `dim (basis n INSERT
           {row i ((lambda k l. if l = n then &0 else (A:real^N^N)$k$l)
                   :real^N^N)
            | i IN (1..dimindex(:N)) DELETE m})` THEN
    CONJ_TAC THENL
     [MATCH_MP_TAC DIM_SUBSET THEN REWRITE_TAC[GSYM IN_NUMSEG] THEN
      MATCH_MP_TAC(SET_RULE
       `m IN s /\ (!i. i IN s DELETE m ==> f i = g i) /\ f m = a
        ==> {f i | i IN s} SUBSET a INSERT {g i | i IN s DELETE m}`) THEN
      ASM_SIMP_TAC[IN_NUMSEG; IN_DELETE; row; LAMBDA_BETA; basis; LAMBDA_ETA];
      REWRITE_TAC[DIM_INSERT] THEN MATCH_MP_TAC(ARITH_RULE
       `n <= k ==> (if p then n else n + 1) <= k + 1`) THEN
      MATCH_MP_TAC(MESON[DIM_LINEAR_IMAGE_LE; DIM_SUBSET; LE_TRANS]
       `(?f. linear f /\ t SUBSET IMAGE f s) ==> dim t <= dim s`) THEN
      EXISTS_TAC `(\x. lambda i. if i = n then &0 else x$i)
                  :real^N->real^N` THEN
      REWRITE_TAC[SUBSET; FORALL_IN_GSPEC] THEN CONJ_TAC THENL
       [SIMP_TAC[linear; CART_EQ; LAMBDA_BETA; VECTOR_ADD_COMPONENT;
                  VECTOR_MUL_COMPONENT] THEN
        REPEAT STRIP_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
        REAL_ARITH_TAC;
        X_GEN_TAC `i:num` THEN REWRITE_TAC[IN_NUMSEG; IN_DELETE] THEN
        STRIP_TAC THEN REWRITE_TAC[IN_IMAGE] THEN
        ONCE_REWRITE_TAC[CONJ_SYM] THEN
        REWRITE_TAC[EXISTS_IN_GSPEC] THEN EXISTS_TAC `i:num` THEN
        ASM_SIMP_TAC[row; CART_EQ; LAMBDA_BETA]]])
  and lemma2 = prove
   (`!A:real^N^N.
          rank A < dimindex(:N)
          ==> ?n x. 1 <= n /\ n <= dimindex(:N) /\
                    rank A <
                    rank((lambda i. if i = n then x else row i A):real^N^N)`,
    REPEAT STRIP_TAC THEN SUBGOAL_THEN
     `?n. 1 <= n /\ n <= dimindex(:N) /\
          row n (A:real^N^N) IN
          span {row j A | j IN (1..dimindex(:N)) DELETE n}`
    MP_TAC THENL
     [MP_TAC(ISPEC `transp A:real^N^N` HOMOGENEOUS_LINEAR_EQUATIONS_DET) THEN
      ASM_REWRITE_TAC[DET_EQ_0_RANK; RANK_TRANSP] THEN
      DISCH_THEN(X_CHOOSE_THEN `c:real^N` STRIP_ASSUME_TAC) THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [CART_EQ]) THEN
      REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; VEC_COMPONENT] THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `n:num` THEN STRIP_TAC THEN
      ASM_REWRITE_TAC[] THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CART_EQ]) THEN
      SIMP_TAC[matrix_vector_mul; transp; VEC_COMPONENT; LAMBDA_BETA] THEN
      DISCH_TAC THEN
      SUBGOAL_THEN `row n A = vsum ((1..dimindex(:N)) DELETE n)
                       (\i. --((c:real^N)$i / c$n) % row i (A:real^N^N))`
      SUBST1_TAC THENL
       [ASM_SIMP_TAC[VSUM_DELETE; FINITE_NUMSEG; IN_NUMSEG; REAL_DIV_REFL] THEN
        REWRITE_TAC[VECTOR_ARITH `n = x - -- &1 % n <=> x:real^N = vec 0`] THEN
        SIMP_TAC[VSUM_COMPONENT; row; VECTOR_MUL_COMPONENT; LAMBDA_BETA;
          CART_EQ; REAL_ARITH `--(x / y) * z:real = --(inv y) * z * x`] THEN
        ASM_SIMP_TAC[SUM_LMUL; VEC_COMPONENT; REAL_MUL_RZERO];
        MATCH_MP_TAC SPAN_VSUM THEN SIMP_TAC[FINITE_DELETE; FINITE_NUMSEG] THEN
        X_GEN_TAC `i:num` THEN REWRITE_TAC[IN_DELETE; IN_NUMSEG] THEN
        STRIP_TAC THEN MATCH_MP_TAC SPAN_MUL THEN
        MATCH_MP_TAC SPAN_SUPERSET THEN ASM SET_TAC[]];
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `n:num` THEN STRIP_TAC THEN
      ASM_REWRITE_TAC[] THEN
      SUBGOAL_THEN `span {row j (A:real^N^N) | j IN (1..dimindex(:N)) DELETE n}
                    PSUBSET (:real^N)`
      MP_TAC THENL
       [REWRITE_TAC[PSUBSET; SUBSET_UNIV] THEN
        DISCH_THEN(MP_TAC o AP_TERM `dim:(real^N->bool)->num`) THEN
        REWRITE_TAC[DIM_UNIV] THEN
        MATCH_MP_TAC(ARITH_RULE `1 <= n /\ x <= n - 1 ==> ~(x = n)`) THEN
        REWRITE_TAC[DIMINDEX_GE_1; DIM_SPAN] THEN
        W(MP_TAC o PART_MATCH (lhand o rand) DIM_LE_CARD o lhand o snd) THEN
        ONCE_REWRITE_TAC[SIMPLE_IMAGE] THEN
        SIMP_TAC[FINITE_IMAGE; FINITE_DELETE; FINITE_NUMSEG] THEN
        MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] LE_TRANS) THEN
        W(MP_TAC o PART_MATCH (lhand o rand) CARD_IMAGE_LE o lhand o snd) THEN
        SIMP_TAC[FINITE_DELETE; FINITE_NUMSEG] THEN
        MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] LE_TRANS) THEN
        ASM_SIMP_TAC[CARD_DELETE; IN_NUMSEG; FINITE_NUMSEG] THEN
        REWRITE_TAC[CARD_NUMSEG_1; LE_REFL];
        DISCH_THEN(MP_TAC o MATCH_MP (SET_RULE
         `s PSUBSET UNIV ==> ?x. ~(x IN s)`)) THEN
        MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `x:real^N` THEN
        REWRITE_TAC[RANK_ROW] THEN DISCH_TAC THEN
        SUBGOAL_THEN
         `!A:real^N^N. rows A = row n A INSERT
                                {row j A | j IN (1..dimindex (:N)) DELETE n}`
         (fun th -> REWRITE_TAC[th])
        THENL
         [REWRITE_TAC[rows; IN_DELETE; IN_NUMSEG] THEN ASM SET_TAC[];
          ASM_SIMP_TAC[DIM_INSERT]] THEN
        COND_CASES_TAC THENL
         [FIRST_X_ASSUM(MP_TAC o check (is_neg o concl)) THEN
          FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (MESON[]
            `x IN span s ==> x = y /\ s = t ==> ~(y IN span t) ==> q`)) THEN
          ASM_SIMP_TAC[row; LAMBDA_BETA; LAMBDA_ETA];
          MATCH_MP_TAC(ARITH_RULE `s = t ==> s < t + 1`) THEN
          AP_TERM_TAC THEN REWRITE_TAC[row]] THEN
        MATCH_MP_TAC(SET_RULE
         `(!x. x IN s ==> f x = g x) ==> {f x | x IN s} = {g x | x IN s}`) THEN
        ASM_SIMP_TAC[IN_DELETE; IN_NUMSEG; LAMBDA_BETA; CART_EQ]]]) in
  GEN_TAC THEN EQ_TAC THEN REWRITE_TAC[lemma1] THEN DISCH_TAC THEN
  MATCH_MP_TAC(ARITH_RULE
   `r <= n /\ ~(r = n) /\ ~(r = n - 1) ==> r < n - 1`) THEN
  REPEAT CONJ_TAC THENL
   [MP_TAC(ISPEC `A:real^N^N` RANK_BOUND) THEN ARITH_TAC;
    REWRITE_TAC[RANK_EQ_FULL_DET] THEN
    MP_TAC(SYM(ISPEC `A:real^N^N` MATRIX_MUL_LEFT_COFACTOR)) THEN
    ASM_REWRITE_TAC[MATRIX_CMUL_EQ_0; TRANSP_MAT; MATRIX_MUL_LZERO] THEN
    REWRITE_TAC[MAT_EQ; ARITH_EQ];
    DISCH_TAC] THEN
  MP_TAC(ISPEC `A:real^N^N` lemma2) THEN
  ASM_REWRITE_TAC[DIMINDEX_GE_1; ARITH_RULE `n - 1 < n <=> 1 <= n`] THEN
  DISCH_THEN(X_CHOOSE_THEN `n:num` (X_CHOOSE_THEN `x:real^N`
    STRIP_ASSUME_TAC)) THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP (ARITH_RULE
   `n - 1 < k ==> k <= MIN n n ==> k = n`)) THEN
  REWRITE_TAC[RANK_BOUND; RANK_EQ_FULL_DET] THEN
  MP_TAC(GEN `A:real^N^N` (ISPECL [`A:real^N^N`; `n:num`]
    DET_COFACTOR_EXPANSION)) THEN
  ASM_SIMP_TAC[] THEN DISCH_THEN(K ALL_TAC) THEN MATCH_MP_TAC SUM_EQ_0 THEN
  X_GEN_TAC `m:num` THEN SIMP_TAC[IN_NUMSEG; REAL_ENTIRE] THEN STRIP_TAC THEN
  DISJ2_TAC THEN FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CART_EQ]) THEN
  DISCH_THEN(MP_TAC o SPEC `n:num`) THEN ASM_REWRITE_TAC[CART_EQ] THEN
  DISCH_THEN(MP_TAC o SPEC `m:num`) THEN
  ASM_SIMP_TAC[MAT_COMPONENT; COND_ID] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] EQ_TRANS) THEN
  ASM_SIMP_TAC[cofactor; LAMBDA_BETA] THEN AP_TERM_TAC THEN
  ASM_SIMP_TAC[CART_EQ; LAMBDA_BETA; row] THEN
  REPEAT STRIP_TAC THEN
  REPEAT(COND_CASES_TAC THEN ASM_SIMP_TAC[LAMBDA_BETA]) THEN
  ASM_MESON_TAC[]);;


let RANK_COFACTOR_EQ_1 = 
prove
 (`!A:real^N^N. rank(cofactor A) = 1 <=>
                dimindex(:N) = 1 \/ rank A = dimindex(:N) - 1`,

  GEN_TAC THEN ASM_CASES_TAC `dimindex(:N) = 1` THENL
   [ASM_MESON_TAC[RANK_COFACTOR_EQ_FULL]; ASM_REWRITE_TAC[]] THEN
  EQ_TAC THENL
   [ASM_CASES_TAC `cofactor A:real^N^N = mat 0` THEN
    ASM_REWRITE_TAC[RANK_0; ARITH_EQ] THEN DISCH_TAC THEN
    MATCH_MP_TAC(ARITH_RULE
     `~(r < n - 1) /\ ~(r = n) /\ r <= MIN n n ==> r = n - 1`) THEN
    ASM_REWRITE_TAC[RANK_BOUND; GSYM COFACTOR_EQ_0] THEN
    MP_TAC(ISPEC `A:real^N^N` RANK_COFACTOR_EQ_FULL) THEN ASM_REWRITE_TAC[];
    DISCH_TAC THEN MATCH_MP_TAC(ARITH_RULE
     `~(n = 0) /\ n <= 1 ==> n = 1`) THEN
    ASM_REWRITE_TAC[RANK_EQ_0; COFACTOR_EQ_0; LT_REFL] THEN
    MP_TAC(ISPECL [`A:real^N^N`; `transp(cofactor A):real^N^N`]
      RANK_SYLVESTER) THEN
    ASM_REWRITE_TAC[MATRIX_MUL_RIGHT_COFACTOR; RANK_TRANSP] THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP (ARITH_RULE
     `a = n - 1 ==> 1 <= n ==> a < n`)) THEN
    ASM_SIMP_TAC[GSYM DET_EQ_0_RANK; DIMINDEX_GE_1] THEN
    DISCH_TAC THEN REWRITE_TAC[MATRIX_CMUL_LZERO; RANK_0] THEN
    ARITH_TAC]);;


let RANK_COFACTOR = 
prove
 (`!A:real^N^N.
        rank(cofactor A) = if rank(A) = dimindex(:N) then dimindex(:N)
                           else if rank(A) = dimindex(:N) - 1 then 1
                           else 0`,

  GEN_TAC THEN COND_CASES_TAC THEN ASM_REWRITE_TAC[RANK_COFACTOR_EQ_FULL] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[RANK_COFACTOR_EQ_1] THEN
  REWRITE_TAC[RANK_EQ_0; COFACTOR_EQ_0] THEN
  MATCH_MP_TAC(ARITH_RULE
   `r <= MIN n n /\ ~(r = n) /\ ~(r = n - 1) ==> r < n - 1`) THEN
  ASM_REWRITE_TAC[RANK_BOUND]);;

(* ------------------------------------------------------------------------- *)
(* Not in so many words, but combining this with intermediate value theorem  *)
(* implies the determinant is an open map.                                   *)
(* ------------------------------------------------------------------------- *)


let DET_OPEN_MAP = 
prove
 (`!A:real^N^N e.
        &0 < e
        ==> (?B:real^N^N. (!i j. abs(B$i$j - A$i$j) < e) /\ det B < det A) /\
            (?C:real^N^N. (!i j. abs(C$i$j - A$i$j) < e) /\ det C > det A)`,

  
let lemma1 = prove
   (`!A:real^N^N i e.
          1 <= i /\ i <= dimindex(:N) /\ row i A = vec 0 /\ &0 < e
          ==> (?B:real^N^N. (!i j. abs(B$i$j - A$i$j) < e) /\ det B < &0) /\
              (?C:real^N^N. (!i j. abs(C$i$j - A$i$j) < e) /\ det C > &0)`,
    REPEAT GEN_TAC THEN STRIP_TAC THEN
    SUBGOAL_THEN `det(A:real^N^N) = &0` ASSUME_TAC THENL
     [ASM_MESON_TAC[DET_ZERO_ROW]; ALL_TAC] THEN
    MP_TAC(ISPEC `A:real^N^N` NEARBY_INVERTIBLE_MATRIX) THEN
    DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `min d e / &2`) THEN
    ANTS_TAC THENL [ASM_REAL_ARITH_TAC; REWRITE_TAC[INVERTIBLE_DET_NZ]] THEN
    DISCH_THEN(STRIP_ASSUME_TAC o MATCH_MP (REAL_ARITH
     `~(x = &0) ==> x < &0 \/ &0 < x`))
    THENL [ALL_TAC; ONCE_REWRITE_TAC[CONJ_SYM]] THEN
    (CONJ_TAC THENL
       [EXISTS_TAC `A + min d e / &2 %% mat 1:real^N^N`;
        EXISTS_TAC `(lambda j. if j = i then
                         --(&1) % row i (A + min d e / &2 %% mat 1:real^N^N)
                         else row j (A + min d e / &2 %% mat 1:real^N^N))
                    :real^N^N`]) THEN
    ASM_SIMP_TAC[DET_ROW_MUL; MESON[]
     `(if j = i then f i else f j) = f j`] THEN
    REWRITE_TAC[row; LAMBDA_ETA] THEN
    ASM_REWRITE_TAC[real_gt; GSYM row] THEN
    TRY(CONJ_TAC THENL [ALL_TAC; ASM_REAL_ARITH_TAC]) THEN
    (MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN
     SUBGOAL_THEN `?k. 1 <= k /\ k <= dimindex(:N) /\ !A:real^N^N. A$m = A$k`
     CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
     SUBGOAL_THEN `?l. 1 <= l /\ l <= dimindex(:N) /\ !z:real^N. z$n = z$l`
     CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC]) THEN
    ASM_SIMP_TAC[LAMBDA_BETA] THEN
    TRY COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_SIMP_TAC[MATRIX_ADD_COMPONENT; MATRIX_CMUL_COMPONENT; MAT_COMPONENT;
                 VECTOR_MUL_COMPONENT] THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CART_EQ]) THEN
    DISCH_THEN(MP_TAC o SPEC `l:num`) THEN
    ASM_SIMP_TAC[row; LAMBDA_BETA; VEC_COMPONENT] THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN ASM_REAL_ARITH_TAC)
  and lemma2 = prove
   (`!A:real^N^N x:real^N i.
          1 <= i /\ i <= dimindex(:N) /\ x$i = &1
          ==> det(lambda k. if k = i then transp A ** x else row k A) = det A`,
    REPEAT STRIP_TAC THEN MATCH_MP_TAC EQ_TRANS THEN
    EXISTS_TAC
     `det(lambda k. if k = i
                    then row i (A:real^N^N) + (transp A ** x - row i A)
                    else row k A)` THEN
    CONJ_TAC THENL
     [REWRITE_TAC[VECTOR_ARITH `r + (x - r):real^N = x`]; ALL_TAC] THEN
    MATCH_MP_TAC DET_ROW_SPAN THEN
    SUBGOAL_THEN
     `transp(A:real^N^N) ** x - row i A =
      vsum ((1..dimindex(:N)) DELETE i) (\k. x$k % row k A)`
    SUBST1_TAC THENL
     [SIMP_TAC[CART_EQ; VSUM_COMPONENT; VECTOR_SUB_COMPONENT; row; transp;
               LAMBDA_BETA; matrix_vector_mul; VECTOR_MUL_COMPONENT] THEN
      ASM_SIMP_TAC[SUM_DELETE; IN_NUMSEG; FINITE_NUMSEG; REAL_MUL_LID] THEN
      REWRITE_TAC[REAL_MUL_AC];
      ASM_REWRITE_TAC[] THEN MATCH_MP_TAC SPAN_VSUM THEN
      REWRITE_TAC[FINITE_DELETE; IN_DELETE; IN_NUMSEG; FINITE_NUMSEG] THEN
      X_GEN_TAC `j:num` THEN STRIP_TAC THEN MATCH_MP_TAC SPAN_MUL THEN
      MATCH_MP_TAC SPAN_SUPERSET THEN ASM SET_TAC[]]) in
  REPEAT GEN_TAC THEN DISCH_TAC THEN
  ASM_CASES_TAC `cofactor(A:real^N^N) = mat 0` THENL
   [MP_TAC(SYM(ISPEC `A:real^N^N` MATRIX_MUL_LEFT_COFACTOR)) THEN
    ASM_REWRITE_TAC[MATRIX_CMUL_EQ_0; TRANSP_MAT; MATRIX_MUL_LZERO] THEN
    REWRITE_TAC[MAT_EQ; ARITH_EQ] THEN STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    SUBGOAL_THEN
     `?c i. 1 <= i /\ i <= dimindex(:N) /\ c$i = &1 /\
            transp(A:real^N^N) ** c = vec 0`
    STRIP_ASSUME_TAC THENL
     [MP_TAC(ISPEC `transp A:real^N^N` HOMOGENEOUS_LINEAR_EQUATIONS_DET) THEN
      ASM_REWRITE_TAC[DET_TRANSP] THEN
      DISCH_THEN(X_CHOOSE_THEN `c:real^N` STRIP_ASSUME_TAC) THEN
      ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [CART_EQ]) THEN
      REWRITE_TAC[VEC_COMPONENT; NOT_IMP; NOT_FORALL_THM] THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `i:num` THEN STRIP_TAC THEN
      EXISTS_TAC `inv(c$i) % c:real^N` THEN
      ASM_SIMP_TAC[VECTOR_MUL_COMPONENT; REAL_MUL_LINV] THEN
      ASM_REWRITE_TAC[MATRIX_VECTOR_MUL_RMUL; VECTOR_MUL_RZERO];
      ALL_TAC] THEN
    MP_TAC(ISPECL
    [`(lambda k. if k = i then transp A ** c else row k (A:real^N^N)):real^N^N`;
     `i:num`; `min e (e / &(dimindex(:N)) /
                      (&1 + norm(&2 % basis i - c:real^N)))`] lemma1) THEN
    ASM_SIMP_TAC[REAL_LT_MIN; REAL_LT_DIV; REAL_OF_NUM_LT; LE_1; DIMINDEX_GE_1;
                 NORM_ARITH `&0 < &1 + norm(x:real^N)`] THEN
    ANTS_TAC THENL
     [ASM_SIMP_TAC[row; CART_EQ; VEC_COMPONENT; LAMBDA_BETA];
      ALL_TAC] THEN
    MATCH_MP_TAC MONO_AND THEN CONJ_TAC THEN
    ABBREV_TAC `A':real^N^N =
                lambda k. if k = i then vec 0 else row k (A:real^N^N)` THEN
    DISCH_THEN(X_CHOOSE_THEN `B:real^N^N` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `(lambda k. if k = i then transp(B:real^N^N) **
                                         (&2 % basis i - c)
                           else row k B):real^N^N` THEN
    ASM_SIMP_TAC[lemma2; BASIS_COMPONENT; VECTOR_MUL_COMPONENT;
                 VECTOR_SUB_COMPONENT; REAL_ARITH `&2 * x - x = x`] THEN
    (MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN
     SUBGOAL_THEN `?k. 1 <= k /\ k <= dimindex(:N) /\ !A:real^N^N. A$m = A$k`
     CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
     SUBGOAL_THEN `?l. 1 <= l /\ l <= dimindex(:N) /\ !z:real^N. z$n = z$l`
     CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC]) THEN
    EXPAND_TAC "A'" THEN ASM_SIMP_TAC[LAMBDA_BETA] THEN
    (COND_CASES_TAC THENL
      [ALL_TAC;
       FIRST_X_ASSUM(MP_TAC o SPECL [`k:num`; `l:num`]) THEN
       EXPAND_TAC "A'" THEN ASM_SIMP_TAC[LAMBDA_BETA; row]] THEN
     SUBGOAL_THEN
      `(A:real^N^N)$k$l = (transp(A':real^N^N) ** (&2 % basis i - c:real^N))$l`
     SUBST1_TAC THENL
      [ASM_SIMP_TAC[matrix_vector_mul; transp; LAMBDA_BETA] THEN
       EXPAND_TAC "A'" THEN ASM_SIMP_TAC[LAMBDA_BETA] THEN
       REWRITE_TAC[COND_RAND; COND_RATOR] THEN
       SIMP_TAC[VECTOR_SUB_COMPONENT; VECTOR_MUL_COMPONENT; BASIS_COMPONENT;
         VEC_COMPONENT; REAL_MUL_RZERO; REAL_SUB_LZERO; REAL_MUL_LZERO] THEN
       ASM_SIMP_TAC[SUM_CASES; FINITE_NUMSEG; SUM_0; REAL_ADD_LID] THEN
       ASM_SIMP_TAC[GSYM DELETE; SUM_DELETE; IN_NUMSEG; FINITE_NUMSEG] THEN
       UNDISCH_TAC `transp(A:real^N^N) ** (c:real^N) = vec 0` THEN
       ASM_SIMP_TAC[CART_EQ; VEC_COMPONENT; matrix_vector_mul; LAMBDA_BETA;
                    row; transp] THEN
       DISCH_THEN(MP_TAC o SPEC `l:num`) THEN ASM_REWRITE_TAC[] THEN
       SIMP_TAC[REAL_MUL_RNEG; SUM_NEG] THEN REAL_ARITH_TAC;
       REWRITE_TAC[GSYM VECTOR_SUB_COMPONENT; GSYM TRANSP_MATRIX_SUB;
                   GSYM MATRIX_VECTOR_MUL_SUB_RDISTRIB]] THEN
      ASM_SIMP_TAC[matrix_vector_mul; transp; LAMBDA_BETA] THEN
      W(MP_TAC o PART_MATCH lhand SUM_ABS_NUMSEG o lhand o snd) THEN
      MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] REAL_LET_TRANS) THEN
      MATCH_MP_TAC SUM_BOUND_LT_GEN THEN
      ASM_SIMP_TAC[FINITE_NUMSEG; NUMSEG_EMPTY;
                   GSYM NOT_LE; DIMINDEX_GE_1] THEN
      X_GEN_TAC `r:num` THEN REWRITE_TAC[CARD_NUMSEG_1; IN_NUMSEG] THEN
      STRIP_TAC THEN REWRITE_TAC[REAL_ABS_MUL] THEN
      TRANS_TAC REAL_LET_TRANS
       `abs((B - A':real^N^N)$r$l) * (&1 + norm(&2 % basis i - c:real^N))` THEN
      CONJ_TAC THENL
       [MATCH_MP_TAC REAL_LE_LMUL THEN REWRITE_TAC[REAL_ABS_POS] THEN
        MATCH_MP_TAC(REAL_ARITH `a <= b ==> a <= &1 + b`) THEN
        ASM_SIMP_TAC[COMPONENT_LE_NORM];
        ASM_SIMP_TAC[MATRIX_SUB_COMPONENT; GSYM REAL_LT_RDIV_EQ;
                     NORM_ARITH `&0 < &1 + norm(x:real^N)`]]);
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE RAND_CONV [CART_EQ]) THEN
    SIMP_TAC[CART_EQ; MAT_COMPONENT; COND_ID] THEN
    REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; real_gt] THEN
    DISCH_THEN(X_CHOOSE_THEN `i:num` (CONJUNCTS_THEN2 STRIP_ASSUME_TAC
     (X_CHOOSE_THEN `j:num` STRIP_ASSUME_TAC))) THEN
    FIRST_ASSUM(DISJ_CASES_TAC o MATCH_MP (REAL_ARITH
     `~(x = &0) ==> &0 < x \/ x < &0`))
    THENL [ALL_TAC; ONCE_REWRITE_TAC[CONJ_SYM]] THEN
    (CONJ_TAC THENL
     [EXISTS_TAC `(lambda m n. if m = i /\ n = j
                               then (A:real^N^N)$i$j -
                                    e / (&1 + abs(cofactor A$i$j))
                               else A$m$n):real^N^N`;
      EXISTS_TAC `(lambda m n. if m = i /\ n = j
                               then (A:real^N^N)$i$j +
                                    e / (&1 + abs(cofactor A$i$j))
                               else A$m$n):real^N^N`]) THEN
     (CONJ_TAC THENL
       [MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN
        SUBGOAL_THEN `?k. 1 <= k /\ k <= dimindex(:N) /\ !A:real^N^N. A$m = A$k`
        CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
        SUBGOAL_THEN `?l. 1 <= l /\ l <= dimindex(:N) /\ !z:real^N. z$n = z$l`
        CHOOSE_TAC THENL [REWRITE_TAC[FINITE_INDEX_INRANGE]; ALL_TAC] THEN
        ASM_SIMP_TAC[LAMBDA_BETA] THEN
        COND_CASES_TAC THEN ASM_REWRITE_TAC[REAL_SUB_REFL; REAL_ABS_NUM] THEN
        REWRITE_TAC[REAL_ARITH `abs(a - e - a) = abs e`;
                    REAL_ARITH `abs((a + e) - a) = abs e`] THEN
        REWRITE_TAC[REAL_ABS_DIV; REAL_ABS_NUM; REAL_ABS_ABS] THEN
        ASM_SIMP_TAC[REAL_ARITH `abs(&1 + abs x) = &1 + abs x`;
                     REAL_LT_LDIV_EQ; REAL_ARITH `&0 < &1 + abs x`] THEN
        MATCH_MP_TAC(REAL_ARITH
         `&0 < e /\ &0 < e * x ==> abs e < e * (&1 + x)`) THEN
        ASM_SIMP_TAC[REAL_LT_MUL_EQ] THEN ASM_REAL_ARITH_TAC;
        ALL_TAC]) THEN
    MP_TAC(GEN `A:real^N^N` (SPECL [`A:real^N^N`; `i:num`]
        DET_COFACTOR_EXPANSION)) THEN
    ASM_SIMP_TAC[] THEN DISCH_THEN(K ALL_TAC) THEN
    ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN
    ASM_SIMP_TAC[GSYM SUM_SUB_NUMSEG; LAMBDA_BETA] THEN
    REWRITE_TAC[REAL_ARITH `p - A$i$j * cofactor A$i$j =
                            --(A$i$j * cofactor A$i$j - p)`] THEN
    REWRITE_TAC[SUM_NEG; REAL_ARITH
     `a * b - c * d:real = b * (a - c) + c * (b - d)`] THEN
    REWRITE_TAC[SUM_ADD_NUMSEG; REAL_NEG_ADD] THEN MATCH_MP_TAC(REAL_ARITH
     `b = &0 /\ &0 < a ==> &0 < a + b`) THEN
    (CONJ_TAC THENL
      [REWRITE_TAC[REAL_NEG_EQ_0] THEN
       MATCH_MP_TAC SUM_EQ_0 THEN X_GEN_TAC `m:num` THEN
       REWRITE_TAC[IN_NUMSEG; REAL_ENTIRE] THEN STRIP_TAC THEN DISJ2_TAC THEN
       REWRITE_TAC[REAL_SUB_0] THEN REWRITE_TAC[cofactor] THEN
       ASM_SIMP_TAC[LAMBDA_BETA] THEN AP_TERM_TAC THEN
       ASM_SIMP_TAC[CART_EQ; LAMBDA_BETA] THEN ASM_MESON_TAC[];
       ALL_TAC]) THEN
    REWRITE_TAC[GSYM SUM_NEG; GSYM REAL_MUL_RNEG] THEN
    MATCH_MP_TAC SUM_POS_LT THEN REWRITE_TAC[FINITE_NUMSEG] THEN
    MATCH_MP_TAC(MESON[REAL_LT_IMP_LE; REAL_LE_REFL]
     `(?i. P i /\ &0 < f i /\ (!j. P j /\ ~(j = i) ==> f j = &0))
      ==> (!j. P j ==> &0 <= f j) /\ (?j. P j /\ &0 < f j)`) THEN
    EXISTS_TAC `j:num` THEN ASM_REWRITE_TAC[FINITE_NUMSEG] THEN
    ASM_SIMP_TAC[REAL_SUB_REFL; REAL_MUL_RZERO; IN_NUMSEG; REAL_NEG_0] THEN
    REWRITE_TAC[REAL_ARITH `a - (a + e):real = --e`;
                REAL_ARITH `a - (a - e):real = e`; REAL_NEG_NEG] THEN
    ASM_SIMP_TAC[REAL_LT_MUL_EQ] THEN
    REWRITE_TAC[REAL_ARITH `&0 < a * --b <=> &0 < --a * b`] THEN
    ASM_SIMP_TAC[REAL_LT_MUL_EQ; REAL_NEG_GT0] THEN
    MATCH_MP_TAC REAL_LT_DIV THEN ASM_REAL_ARITH_TAC]);;

(* ------------------------------------------------------------------------- *)
(* Infinite sums of vectors. Allow general starting point (and more).        *)
(* ------------------------------------------------------------------------- *)

parse_as_infix("sums",(12,"right"));;


let sums = new_definition
  `(f sums l) s = ((\n. vsum(s INTER (0..n)) f) --> l) sequentially`;;


let infsum = new_definition
 `infsum s f = @l. (f sums l) s`;;


let summable = new_definition
 `summable s f = ?l. (f sums l) s`;;


let SUMS_SUMMABLE = 
prove
 (`!f l s. (f sums l) s ==> summable s f`,

  REWRITE_TAC[summable] THEN MESON_TAC[]);;


let SUMS_INFSUM = 
prove
 (`!f s. (f sums (infsum s f)) s <=> summable s f`,

  REWRITE_TAC[infsum; summable] THEN MESON_TAC[]);;


let SUMS_LIM = 
prove
 (`!f:num->real^N s.
      (f sums lim sequentially (\n. vsum (s INTER (0..n)) f)) s
      <=> summable s f`,

  GEN_TAC THEN GEN_TAC THEN EQ_TAC THENL [MESON_TAC[summable];
  REWRITE_TAC[summable; sums] THEN STRIP_TAC THEN REWRITE_TAC[lim] THEN
  ASM_MESON_TAC[]]);;


let FINITE_INTER_NUMSEG = 
prove
 (`!s m n. FINITE(s INTER (m..n))`,


let SERIES_FROM = 
prove
 (`!f l k. (f sums l) (from k) = ((\n. vsum(k..n) f) --> l) sequentially`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sums] THEN
  AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN
  AP_THM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; numseg; from; IN_ELIM_THM; IN_INTER] THEN ARITH_TAC);;


let SERIES_UNIQUE = 
prove
 (`!f:num->real^N l l' s. (f sums l) s /\ (f sums l') s ==> (l = l')`,

  REWRITE_TAC[sums] THEN MESON_TAC[TRIVIAL_LIMIT_SEQUENTIALLY; LIM_UNIQUE]);;


let INFSUM_UNIQUE = 
prove
 (`!f:num->real^N l s. (f sums l) s ==> infsum s f = l`,

  MESON_TAC[SERIES_UNIQUE; SUMS_INFSUM; summable]);;


let SERIES_TERMS_TOZERO = 
prove
 (`!f l n. (f sums l) (from n) ==> (f --> vec 0) sequentially`,

  REPEAT GEN_TAC THEN SIMP_TAC[sums; LIM_SEQUENTIALLY; FROM_INTER_NUMSEG] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN DISCH_THEN(X_CHOOSE_TAC `N:num`) THEN
  EXISTS_TAC `N + n + 1` THEN X_GEN_TAC `m:num` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(fun th ->
    MP_TAC(SPEC `m - 1` th) THEN MP_TAC(SPEC `m:num` th)) THEN
  SUBGOAL_THEN `0 < m /\ n <= m` (fun th -> SIMP_TAC[VSUM_CLAUSES_RIGHT; th])
  THENL [ASM_ARITH_TAC; ALL_TAC] THEN
  REPEAT(ANTS_TAC THENL [ASM_ARITH_TAC; DISCH_TAC]) THEN
  REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC);;


let SERIES_FINITE = 
prove
 (`!f s. FINITE s ==> (f sums (vsum s f)) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[num_FINITE; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `n:num` THEN REWRITE_TAC[sums; LIM_SEQUENTIALLY] THEN
  DISCH_TAC THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN EXISTS_TAC `n:num` THEN
  X_GEN_TAC `m:num` THEN DISCH_TAC THEN
  SUBGOAL_THEN `s INTER (0..m) = s`
   (fun th -> ASM_REWRITE_TAC[th; DIST_REFL]) THEN
  REWRITE_TAC[EXTENSION; IN_INTER; IN_NUMSEG; LE_0] THEN
  ASM_MESON_TAC[LE_TRANS]);;


let SERIES_LINEAR = 
prove
 (`!f h l s. (f sums l) s /\ linear h ==> ((\n. h(f n)) sums h l) s`,

  SIMP_TAC[sums; LIM_LINEAR; FINITE_INTER; FINITE_NUMSEG;
           GSYM(REWRITE_RULE[o_DEF] LINEAR_VSUM)]);;


let SERIES_0 = 
prove
 (`!s. ((\n. vec 0) sums (vec 0)) s`,

  REWRITE_TAC[sums; VSUM_0; LIM_CONST]);;


let SERIES_ADD = 
prove
 (`!x x0 y y0 s.
     (x sums x0) s /\ (y sums y0) s ==> ((\n. x n + y n) sums (x0 + y0)) s`,

  SIMP_TAC[sums; FINITE_INTER_NUMSEG; VSUM_ADD; LIM_ADD]);;


let SERIES_SUB = 
prove
 (`!x x0 y y0 s.
     (x sums x0) s /\ (y sums y0) s ==> ((\n. x n - y n) sums (x0 - y0)) s`,

  SIMP_TAC[sums; FINITE_INTER_NUMSEG; VSUM_SUB; LIM_SUB]);;


let SERIES_CMUL = 
prove
 (`!x x0 c s. (x sums x0) s ==> ((\n. c % x n) sums (c % x0)) s`,

  SIMP_TAC[sums; FINITE_INTER_NUMSEG; VSUM_LMUL; LIM_CMUL]);;


let SERIES_NEG = 
prove
 (`!x x0 s. (x sums x0) s ==> ((\n. --(x n)) sums (--x0)) s`,

  SIMP_TAC[sums; FINITE_INTER_NUMSEG; VSUM_NEG; LIM_NEG]);;


let SUMS_IFF = 
prove
 (`!f g k. (!x. x IN k ==> f x = g x) ==> ((f sums l) k <=> (g sums l) k)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[sums] THEN
  AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN
  MATCH_MP_TAC VSUM_EQ THEN ASM_SIMP_TAC[IN_INTER]);;


let SUMS_EQ = 
prove
 (`!f g k. (!x. x IN k ==> f x = g x) /\ (f sums l) k ==> (g sums l) k`,

  MESON_TAC[SUMS_IFF]);;


let SUMS_0 = 
prove
 (`!f:num->real^N s. (!n. n IN s ==> f n = vec 0) ==> (f sums vec 0) s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUMS_EQ THEN
  EXISTS_TAC `\n:num. vec 0:real^N` THEN ASM_SIMP_TAC[SERIES_0]);;


let SERIES_FINITE_SUPPORT = 
prove
 (`!f:num->real^N s k.
     FINITE (s INTER k) /\ (!x. x IN k /\ ~(x IN s) ==> f x = vec 0)
     ==> (f sums vsum (s INTER k) f) k`,

  REWRITE_TAC[sums; LIM_SEQUENTIALLY] THEN REPEAT STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o ISPEC `\x:num. x` o MATCH_MP UPPER_BOUND_FINITE_SET) THEN
  REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  STRIP_TAC THEN X_GEN_TAC `n:num` THEN DISCH_TAC THEN
  SUBGOAL_THEN `vsum (k INTER (0..n)) (f:num->real^N) = vsum(s INTER k) f`
   (fun th -> ASM_REWRITE_TAC[DIST_REFL; th]) THEN
  MATCH_MP_TAC VSUM_SUPERSET THEN
  ASM_SIMP_TAC[SUBSET; IN_INTER; IN_NUMSEG; LE_0] THEN
  ASM_MESON_TAC[IN_INTER; LE_TRANS]);;


let SERIES_COMPONENT = 
prove
 (`!f s l:real^N k. (f sums l) s /\ 1 <= k /\ k <= dimindex(:N)
                    ==> ((\i. lift(f(i)$k)) sums lift(l$k)) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sums] THEN STRIP_TAC THEN
  ONCE_REWRITE_TAC[GSYM o_DEF] THEN
  ASM_SIMP_TAC[GSYM LIFT_SUM; GSYM VSUM_COMPONENT;
               FINITE_INTER; FINITE_NUMSEG] THEN
  ASM_SIMP_TAC[o_DEF; LIM_COMPONENT]);;


let SERIES_DIFFS = 
prove
 (`!f:num->real^N k.
        (f --> vec 0) sequentially
        ==> ((\n. f(n) - f(n + 1)) sums f(k)) (from k)`,

  REWRITE_TAC[sums; FROM_INTER_NUMSEG; VSUM_DIFFS] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC LIM_TRANSFORM_EVENTUALLY THEN
  EXISTS_TAC `\n. (f:num->real^N) k - f(n + 1)` THEN CONJ_TAC THENL
   [REWRITE_TAC[EVENTUALLY_SEQUENTIALLY] THEN EXISTS_TAC `k:num` THEN
    SIMP_TAC[];
    GEN_REWRITE_TAC LAND_CONV [GSYM VECTOR_SUB_RZERO] THEN
    MATCH_MP_TAC LIM_SUB THEN REWRITE_TAC[LIM_CONST] THEN
    MATCH_MP_TAC SEQ_OFFSET THEN ASM_REWRITE_TAC[]]);;


let SERIES_TRIVIAL = 
prove
 (`!f. (f sums vec 0) {}`,

  REWRITE_TAC[sums; INTER_EMPTY; VSUM_CLAUSES; LIM_CONST]);;


let SERIES_RESTRICT = 
prove
 (`!f k l:real^N.
        ((\n. if n IN k then f(n) else vec 0) sums l) (:num) <=>
        (f sums l) k`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sums] THEN
  AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[FUN_EQ_THM; INTER_UNIV] THEN GEN_TAC THEN
  MATCH_MP_TAC(MESON[] `vsum s f = vsum t f /\ vsum t f = vsum t g
                        ==> vsum s f = vsum t g`) THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC VSUM_SUPERSET THEN SET_TAC[];
    MATCH_MP_TAC VSUM_EQ THEN SIMP_TAC[IN_INTER]]);;


let SERIES_VSUM = 
prove
 (`!f l k s. FINITE s /\ s SUBSET k /\ (!x. ~(x IN s) ==> f x = vec 0) /\
             vsum s f = l ==> (f sums l) k`,

  REPEAT STRIP_TAC THEN EXPAND_TAC "l" THEN
  SUBGOAL_THEN `s INTER k = s:num->bool` ASSUME_TAC THENL
   [ASM SET_TAC []; ASM_MESON_TAC [SERIES_FINITE_SUPPORT]]);;


let SUMS_REINDEX = 
prove
 (`!k a l:real^N n.
   ((\x. a(x + k)) sums l) (from n) <=> (a sums l) (from(n + k))`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sums; FROM_INTER_NUMSEG] THEN
  REPEAT GEN_TAC THEN REWRITE_TAC[GSYM VSUM_OFFSET] THEN
  REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  ASM_MESON_TAC[ARITH_RULE `N + k:num <= n ==> n = (n - k) + k /\ N <= n - k`;
                ARITH_RULE `N + k:num <= n ==> N <= n + k`]);;


let SUMS_REINDEX_GEN = 
prove
 (`!k a l:real^N s.
     ((\x. a(x + k)) sums l) s <=> (a sums l) (IMAGE (\i. i + k) s)`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[GSYM SERIES_RESTRICT] THEN
  MP_TAC(ISPECL
   [`k:num`;
    `\i. if i IN IMAGE (\i. i + k) s then (a:num->real^N) i else vec 0`;
    `l:real^N`; `0`] SUMS_REINDEX) THEN
  REWRITE_TAC[FROM_0] THEN
  SIMP_TAC[EQ_ADD_RCANCEL; SET_RULE
   `(!x y:num. x + k = y + k <=> x = y)
         ==> ((x + k) IN IMAGE (\i. i + k) s <=> x IN s)`] THEN
  DISCH_THEN SUBST1_TAC THEN
  GEN_REWRITE_TAC LAND_CONV [GSYM SERIES_RESTRICT] THEN
  AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[FUN_EQ_THM; IN_FROM; ADD_CLAUSES] THEN
  SUBGOAL_THEN `!x:num. x IN IMAGE (\i. i + k) s ==> k <= x` MP_TAC THENL
   [REWRITE_TAC[FORALL_IN_IMAGE] THEN ARITH_TAC; SET_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Similar combining theorems just for summability.                          *)
(* ------------------------------------------------------------------------- *)


let SUMMABLE_LINEAR = 
prove
 (`!f h s. summable s f /\ linear h ==> summable s (\n. h(f n))`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_LINEAR]);;


let SUMMABLE_0 = 
prove
 (`!s. summable s (\n. vec 0)`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_0]);;


let SUMMABLE_ADD = 
prove
 (`!x y s. summable s x /\ summable s y ==> summable s (\n. x n + y n)`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_ADD]);;


let SUMMABLE_SUB = 
prove
 (`!x y s. summable s x /\ summable s y ==> summable s (\n. x n - y n)`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_SUB]);;


let SUMMABLE_CMUL = 
prove
 (`!s x c. summable s x ==> summable s (\n. c % x n)`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_CMUL]);;


let SUMMABLE_NEG = 
prove
 (`!x s. summable s x ==> summable s (\n. --(x n))`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_NEG]);;


let SUMMABLE_IFF = 
prove
 (`!f g k. (!x. x IN k ==> f x = g x) ==> (summable k f <=> summable k g)`,

  REWRITE_TAC[summable] THEN MESON_TAC[SUMS_IFF]);;


let SUMMABLE_EQ = 
prove
 (`!f g k. (!x. x IN k ==> f x = g x) /\ summable k f ==> summable k g`,

  REWRITE_TAC[summable] THEN MESON_TAC[SUMS_EQ]);;


let SUMMABLE_COMPONENT = 
prove
 (`!f:num->real^N s k.
        summable s f /\ 1 <= k /\ k <= dimindex(:N)
        ==> summable s (\i. lift(f(i)$k))`,

  REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(X_CHOOSE_TAC `l:real^N` o REWRITE_RULE[summable]) THEN
  REWRITE_TAC[summable] THEN EXISTS_TAC `lift((l:real^N)$k)` THEN
  ASM_SIMP_TAC[SERIES_COMPONENT]);;


let SERIES_SUBSET = 
prove
 (`!x s t l.
        s SUBSET t /\
        ((\i. if i IN s then x i else vec 0) sums l) t
        ==> (x sums l) s`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
  REWRITE_TAC[sums] THEN MATCH_MP_TAC EQ_IMP THEN
  AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN
  ASM_SIMP_TAC[GSYM VSUM_RESTRICT_SET; FINITE_INTER_NUMSEG] THEN
  AP_THM_TAC THEN AP_TERM_TAC THEN POP_ASSUM MP_TAC THEN SET_TAC[]);;


let SUMMABLE_SUBSET = 
prove
 (`!x s t.
        s SUBSET t /\
        summable t (\i. if i IN s then x i else vec 0)
        ==> summable s x`,

  REWRITE_TAC[summable] THEN MESON_TAC[SERIES_SUBSET]);;


let SUMMABLE_TRIVIAL = 
prove
 (`!f:num->real^N. summable {} f`,

  GEN_TAC THEN REWRITE_TAC[summable] THEN EXISTS_TAC `vec 0:real^N` THEN
  REWRITE_TAC[SERIES_TRIVIAL]);;


let SUMMABLE_RESTRICT = 
prove
 (`!f:num->real^N k.
        summable (:num) (\n. if n IN k then f(n) else vec 0) <=>
        summable k f`,

  REWRITE_TAC[summable; SERIES_RESTRICT]);;


let SUMS_FINITE_DIFF = 
prove
 (`!f:num->real^N t s l.
        t SUBSET s /\ FINITE t /\ (f sums l) s
        ==> (f sums (l - vsum t f)) (s DIFF t)`,

  REPEAT GEN_TAC THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  FIRST_ASSUM(MP_TAC o ISPEC `f:num->real^N` o MATCH_MP SERIES_FINITE) THEN
  ONCE_REWRITE_TAC[GSYM SERIES_RESTRICT] THEN
  REWRITE_TAC[IMP_IMP] THEN ONCE_REWRITE_TAC[CONJ_SYM] THEN
  DISCH_THEN(MP_TAC o MATCH_MP SERIES_SUB) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `x:num` THEN REWRITE_TAC[IN_DIFF] THEN
  FIRST_ASSUM(MP_TAC o SPEC `x:num` o GEN_REWRITE_RULE I [SUBSET]) THEN
  MAP_EVERY ASM_CASES_TAC [`(x:num) IN s`; `(x:num) IN t`] THEN
  ASM_REWRITE_TAC[] THEN VECTOR_ARITH_TAC);;


let SUMS_FINITE_UNION = 
prove
 (`!f:num->real^N s t l.
        FINITE t /\ (f sums l) s
        ==> (f sums (l + vsum (t DIFF s) f)) (s UNION t)`,

  REPEAT GEN_TAC THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  FIRST_ASSUM(MP_TAC o SPEC `s:num->bool` o MATCH_MP FINITE_DIFF) THEN
  DISCH_THEN(MP_TAC o ISPEC `f:num->real^N` o MATCH_MP SERIES_FINITE) THEN
  ONCE_REWRITE_TAC[GSYM SERIES_RESTRICT] THEN
  REWRITE_TAC[IMP_IMP] THEN ONCE_REWRITE_TAC[CONJ_SYM] THEN
  DISCH_THEN(MP_TAC o MATCH_MP SERIES_ADD) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `x:num` THEN
  REWRITE_TAC[IN_DIFF; IN_UNION] THEN
  MAP_EVERY ASM_CASES_TAC [`(x:num) IN s`; `(x:num) IN t`] THEN
  ASM_REWRITE_TAC[] THEN VECTOR_ARITH_TAC);;


let SUMS_OFFSET = 
prove
 (`!f l:real^N m n.
           (f sums l) (from m) /\ 0 < n /\ m <= n
           ==> (f sums l - vsum (m..n - 1) f) (from n)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `from n = from m DIFF (m..(n-1))` SUBST1_TAC THENL
   [REWRITE_TAC[EXTENSION; IN_FROM; IN_DIFF; IN_NUMSEG] THEN ASM_ARITH_TAC;
    MATCH_MP_TAC SUMS_FINITE_DIFF THEN ASM_REWRITE_TAC[FINITE_NUMSEG] THEN
    SIMP_TAC[SUBSET; IN_FROM; IN_NUMSEG]]);;


let SUMS_OFFSET_REV = 
prove
 (`!f:num->real^N l m n.
        (f sums l) (from m) /\ 0 < m /\ n <= m

        ==> (f sums (l + vsum(n..m-1) f)) (from n)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:num->real^N`; `from m`; `n..m-1`; `l:real^N`]
                SUMS_FINITE_UNION) THEN
  ASM_REWRITE_TAC[FINITE_NUMSEG] THEN MATCH_MP_TAC EQ_IMP THEN
  BINOP_TAC THENL [AP_TERM_TAC THEN AP_THM_TAC THEN AP_TERM_TAC; ALL_TAC] THEN
  REWRITE_TAC[EXTENSION; IN_DIFF; IN_UNION; IN_FROM; IN_NUMSEG] THEN
  ASM_ARITH_TAC);;


let SUMMABLE_REINDEX = 
prove
 (`!k a n. summable (from n) (\x. a (x + k)) <=> summable (from(n + k)) a`,

  REWRITE_TAC[summable; GSYM SUMS_REINDEX]);;


let SERIES_DROP_LE = 
prove
 (`!f g s a b.
        (f sums a) s /\ (g sums b) s /\
        (!x. x IN s ==> drop(f x) <= drop(g x))
        ==> drop a <= drop b`,

  REWRITE_TAC[sums] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_DROP_LE) THEN
  REWRITE_TAC[EVENTUALLY_SEQUENTIALLY; TRIVIAL_LIMIT_SEQUENTIALLY] THEN
  EXISTS_TAC `\n. vsum (s INTER (0..n)) (f:num->real^1)` THEN
  EXISTS_TAC `\n. vsum (s INTER (0..n)) (g:num->real^1)` THEN
  ASM_REWRITE_TAC[DROP_VSUM] THEN EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SUM_LE THEN
  ASM_SIMP_TAC[FINITE_INTER; FINITE_NUMSEG; o_THM; IN_INTER; IN_NUMSEG]);;


let SERIES_DROP_POS = 
prove
 (`!f s a.
        (f sums a) s /\ (!x. x IN s ==> &0 <= drop(f x))
        ==> &0 <= drop a`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`(\n. vec 0):num->real^1`; `f:num->real^1`; `s:num->bool`;
                 `vec 0:real^1`; `a:real^1`] SERIES_DROP_LE) THEN
  ASM_SIMP_TAC[SUMS_0; DROP_VEC]);;


let SERIES_BOUND = 
prove
 (`!f:num->real^N g s a b.
        (f sums a) s /\ ((lift o g) sums (lift b)) s /\
        (!i. i IN s ==> norm(f i) <= g i)
        ==> norm(a) <= b`,

  REWRITE_TAC[sums] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_NORM_UBOUND) THEN
  EXISTS_TAC `\n. vsum (s INTER (0..n)) (f:num->real^N)` THEN
  ASM_REWRITE_TAC[TRIVIAL_LIMIT_SEQUENTIALLY] THEN
  REWRITE_TAC[EVENTUALLY_SEQUENTIALLY] THEN EXISTS_TAC `0` THEN
  X_GEN_TAC `m:num` THEN DISCH_TAC THEN
  TRANS_TAC REAL_LE_TRANS `sum (s INTER (0..m)) g` THEN CONJ_TAC THEN
  ASM_SIMP_TAC[VSUM_NORM_LE; IN_INTER; FINITE_NUMSEG; FINITE_INTER] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[GSYM sums]) THEN
  UNDISCH_TAC `((lift o g) sums lift b) s` THEN
  GEN_REWRITE_TAC LAND_CONV [GSYM SERIES_RESTRICT] THEN
  REWRITE_TAC[GSYM FROM_0] THEN DISCH_THEN(MP_TAC o SPEC `m + 1` o MATCH_MP
   (ONCE_REWRITE_RULE[IMP_CONJ] SUMS_OFFSET)) THEN
  ANTS_TAC THENL [ASM_ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[ARITH_RULE `0 < m + 1`; o_DEF; ADD_SUB] THEN
  REWRITE_TAC[GSYM VSUM_RESTRICT_SET] THEN
  REWRITE_TAC[VSUM_REAL; o_DEF; LIFT_DROP; ETA_AX] THEN
  DISCH_THEN(MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ] SERIES_DROP_POS)) THEN
  REWRITE_TAC[DROP_SUB; LIFT_DROP; ONCE_REWRITE_RULE[INTER_COMM] (GSYM INTER);
              REAL_SUB_LE] THEN
  DISCH_THEN MATCH_MP_TAC THEN REPEAT STRIP_TAC THEN COND_CASES_TAC THEN
  ASM_SIMP_TAC[LIFT_DROP; DROP_VEC; REAL_LE_REFL] THEN
  ASM_MESON_TAC[NORM_ARITH `norm(x:real^N) <= y ==> &0 <= y`]);;

(* ------------------------------------------------------------------------- *)
(* Similar combining theorems for infsum.                                    *)
(* ------------------------------------------------------------------------- *)


let INFSUM_LINEAR = 
prove
 (`!f h s. summable s f /\ linear h
           ==> infsum s (\n. h(f n)) = h(infsum s f)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INFSUM_UNIQUE THEN
  MATCH_MP_TAC SERIES_LINEAR THEN ASM_REWRITE_TAC[SUMS_INFSUM]);;


let INFSUM_0 = 
prove
 (`infsum s (\i. vec 0) = vec 0`,

  MATCH_MP_TAC INFSUM_UNIQUE THEN REWRITE_TAC[SERIES_0]);;


let INFSUM_ADD = 
prove
 (`!x y s. summable s x /\ summable s y
           ==> infsum s (\i. x i + y i) = infsum s x + infsum s y`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INFSUM_UNIQUE THEN
  MATCH_MP_TAC SERIES_ADD THEN ASM_REWRITE_TAC[SUMS_INFSUM]);;


let INFSUM_SUB = 
prove
 (`!x y s. summable s x /\ summable s y
           ==> infsum s (\i. x i - y i) = infsum s x - infsum s y`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INFSUM_UNIQUE THEN
  MATCH_MP_TAC SERIES_SUB THEN ASM_REWRITE_TAC[SUMS_INFSUM]);;


let INFSUM_CMUL = 
prove
 (`!s x c. summable s x ==> infsum s (\n. c % x n) = c % infsum s x`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INFSUM_UNIQUE THEN
  MATCH_MP_TAC SERIES_CMUL THEN ASM_REWRITE_TAC[SUMS_INFSUM]);;


let INFSUM_NEG = 
prove
 (`!s x. summable s x ==> infsum s (\n. --(x n)) = --(infsum s x)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC INFSUM_UNIQUE THEN
  MATCH_MP_TAC SERIES_NEG THEN ASM_REWRITE_TAC[SUMS_INFSUM]);;


let INFSUM_EQ = 
prove
 (`!f g k. summable k f /\ summable k g /\ (!x. x IN k ==> f x = g x)
           ==> infsum k f = infsum k g`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[infsum] THEN
  AP_TERM_TAC THEN ABS_TAC THEN ASM_MESON_TAC[SUMS_EQ; SUMS_INFSUM]);;


let INFSUM_RESTRICT = 
prove
 (`!k a:num->real^N.
        infsum (:num) (\n. if n IN k then a n else vec 0) = infsum k a`,

  REPEAT GEN_TAC THEN
  MP_TAC(ISPECL [`a:num->real^N`; `k:num->bool`] SUMMABLE_RESTRICT) THEN
  ASM_CASES_TAC `summable k (a:num->real^N)` THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THENL
   [MATCH_MP_TAC INFSUM_UNIQUE THEN
    ASM_REWRITE_TAC[SERIES_RESTRICT; SUMS_INFSUM];
    RULE_ASSUM_TAC(REWRITE_RULE[summable; NOT_EXISTS_THM]) THEN
    ASM_REWRITE_TAC[infsum]]);;


let PARTIAL_SUMS_COMPONENT_LE_INFSUM = 
prove
 (`!f:num->real^N s k n.
        1 <= k /\ k <= dimindex(:N) /\
        (!i. i IN s ==> &0 <= (f i)$k) /\
        summable s f
        ==> (vsum (s INTER (0..n)) f)$k <= (infsum s f)$k`,

  REPEAT GEN_TAC THEN REWRITE_TAC[GSYM SUMS_INFSUM] THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  REWRITE_TAC[sums; LIM_SEQUENTIALLY] THEN DISCH_TAC THEN
  REWRITE_TAC[GSYM REAL_NOT_LT] THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC
   `vsum (s INTER (0..n)) (f:num->real^N)$k - (infsum s f)$k`) THEN
  ASM_REWRITE_TAC[REAL_SUB_LT] THEN
  DISCH_THEN(X_CHOOSE_THEN `N:num` (MP_TAC o SPEC `N + n:num`)) THEN
  REWRITE_TAC[LE_ADD; REAL_NOT_LT; dist] THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN
  EXISTS_TAC `abs((vsum (s INTER (0..N + n)) f - infsum s f:real^N)$k)` THEN
  ASM_SIMP_TAC[COMPONENT_LE_NORM] THEN REWRITE_TAC[VECTOR_SUB_COMPONENT] THEN
  MATCH_MP_TAC(REAL_ARITH `s < a /\ a <= b ==> a - s <= abs(b - s)`) THEN
  ASM_REWRITE_TAC[] THEN ONCE_REWRITE_TAC[ADD_SYM] THEN
  SIMP_TAC[NUMSEG_ADD_SPLIT; LE_0; UNION_OVER_INTER] THEN
  W(MP_TAC o PART_MATCH (lhs o rand) VSUM_UNION o lhand o rand o snd) THEN
  ANTS_TAC THENL
   [SIMP_TAC[FINITE_INTER; FINITE_NUMSEG; DISJOINT; EXTENSION] THEN
    REWRITE_TAC[IN_INTER; NOT_IN_EMPTY; IN_NUMSEG] THEN ARITH_TAC;
    DISCH_THEN SUBST1_TAC THEN
    REWRITE_TAC[REAL_LE_ADDR; VECTOR_ADD_COMPONENT] THEN
    ASM_SIMP_TAC[VSUM_COMPONENT] THEN MATCH_MP_TAC SUM_POS_LE THEN
    ASM_SIMP_TAC[FINITE_INTER; IN_INTER; FINITE_NUMSEG]]);;


let PARTIAL_SUMS_DROP_LE_INFSUM = 
prove
 (`!f s n.
        (!i. i IN s ==> &0 <= drop(f i)) /\
        summable s f
        ==> drop(vsum (s INTER (0..n)) f) <= drop(infsum s f)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[drop] THEN
  MATCH_MP_TAC PARTIAL_SUMS_COMPONENT_LE_INFSUM THEN
  ASM_REWRITE_TAC[DIMINDEX_1; LE_REFL; GSYM drop]);;

(* ------------------------------------------------------------------------- *)
(* Cauchy criterion for series.                                              *)
(* ------------------------------------------------------------------------- *)


let SEQUENCE_CAUCHY_WLOG = 
prove
 (`!P s. (!m n:num. P m /\ P n ==> dist(s m,s n) < e) <=>
         (!m n. P m /\ P n /\ m <= n ==> dist(s m,s n) < e)`,

  MESON_TAC[DIST_SYM; LE_CASES]);;


let VSUM_DIFF_LEMMA = 
prove
 (`!f:num->real^N k m n.
        m <= n
        ==> vsum(k INTER (0..n)) f - vsum(k INTER (0..m)) f =
            vsum(k INTER (m+1..n)) f`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:num->real^N`; `k INTER (0..n)`; `k INTER (0..m)`]
    VSUM_DIFF) THEN
  ANTS_TAC THENL
   [SIMP_TAC[FINITE_INTER; FINITE_NUMSEG] THEN MATCH_MP_TAC
     (SET_RULE `s SUBSET t ==> (u INTER s SUBSET u INTER t)`) THEN
    REWRITE_TAC[SUBSET; IN_NUMSEG] THEN POP_ASSUM MP_TAC THEN ARITH_TAC;
    DISCH_THEN(SUBST1_TAC o SYM) THEN AP_THM_TAC THEN AP_TERM_TAC THEN
    REWRITE_TAC[SET_RULE
     `(k INTER s) DIFF (k INTER t) = k INTER (s DIFF t)`] THEN
    AP_TERM_TAC THEN REWRITE_TAC[EXTENSION; IN_DIFF; IN_NUMSEG] THEN
    POP_ASSUM MP_TAC THEN ARITH_TAC]);;


let NORM_VSUM_TRIVIAL_LEMMA = 
prove
 (`!e. &0 < e ==> (P ==> norm(vsum(s INTER (m..n)) f) < e <=>
                   P ==> n < m \/ norm(vsum(s INTER (m..n)) f) < e)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `n:num < m` THEN ASM_REWRITE_TAC[] THEN
  FIRST_X_ASSUM(SUBST1_TAC o GEN_REWRITE_RULE I [GSYM NUMSEG_EMPTY]) THEN
  ASM_REWRITE_TAC[VSUM_CLAUSES; NORM_0; INTER_EMPTY]);;


let SERIES_CAUCHY = 
prove
 (`!f s. (?l. (f sums l) s) =
         !e. &0 < e
             ==> ?N. !m n. m >= N
                           ==> norm(vsum(s INTER (m..n)) f) < e`,

  REPEAT GEN_TAC THEN REWRITE_TAC[sums; CONVERGENT_EQ_CAUCHY; cauchy] THEN
  REWRITE_TAC[SEQUENCE_CAUCHY_WLOG] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
  SIMP_TAC[dist; VSUM_DIFF_LEMMA; NORM_VSUM_TRIVIAL_LEMMA] THEN
  REWRITE_TAC[GE; TAUT `a ==> b \/ c <=> a /\ ~b ==> c`] THEN
  REWRITE_TAC[NOT_LT; ARITH_RULE
   `(N <= m /\ N <= n /\ m <= n) /\ m + 1 <= n <=>
    N + 1 <= m + 1 /\ m + 1 <= n`] THEN
  AP_TERM_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  EQ_TAC THEN DISCH_THEN(X_CHOOSE_TAC `N:num`) THENL
   [EXISTS_TAC `N + 1`; EXISTS_TAC `N:num`] THEN
  REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[ARITH_RULE `N + 1 <= m + 1 ==> N <= m + 1`] THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`m - 1`; `n:num`]) THEN
  SUBGOAL_THEN `m - 1 + 1 = m` SUBST_ALL_TAC THENL
   [ALL_TAC; ANTS_TAC THEN SIMP_TAC[]] THEN
  ASM_ARITH_TAC);;


let SUMMABLE_CAUCHY = 
prove
 (`!f s. summable s f <=>
         !e. &0 < e
             ==> ?N. !m n. m >= N ==> norm(vsum(s INTER (m..n)) f) < e`,

  REWRITE_TAC[summable; GSYM SERIES_CAUCHY]);;


let SUMMABLE_IFF_EVENTUALLY = 
prove
 (`!f g k. (?N. !n. N <= n /\ n IN k ==> f n = g n)
           ==> (summable k f <=> summable k g)`,

  REWRITE_TAC[summable; SERIES_CAUCHY] THEN REPEAT GEN_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `N0:num` STRIP_ASSUME_TAC) THEN
  AP_TERM_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `e:real` THEN
  AP_TERM_TAC THEN EQ_TAC THEN
  DISCH_THEN(X_CHOOSE_THEN `N1:num`
   (fun th -> EXISTS_TAC `N0 + N1:num` THEN MP_TAC th)) THEN
  REPEAT(MATCH_MP_TAC MONO_FORALL THEN GEN_TAC) THEN
  DISCH_THEN(fun th -> DISCH_TAC THEN MP_TAC th) THEN
  (ANTS_TAC THENL [ASM_ARITH_TAC; ALL_TAC]) THEN
  MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN AP_TERM_TAC THEN AP_TERM_TAC THEN
  MATCH_MP_TAC VSUM_EQ THEN ASM_SIMP_TAC[IN_INTER; IN_NUMSEG] THEN
  REPEAT STRIP_TAC THENL [ALL_TAC; CONV_TAC SYM_CONV] THEN
  FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[] THEN
  ASM_ARITH_TAC);;


let SUMMABLE_EQ_EVENTUALLY = 
prove
 (`!f g k. (?N. !n. N <= n /\ n IN k ==> f n = g n) /\ summable k f
           ==> summable k g`,


let SUMMABLE_IFF_COFINITE = 
prove
 (`!f s t. FINITE((s DIFF t) UNION (t DIFF s))
           ==> (summable s f <=> summable t f)`,

  REPEAT STRIP_TAC THEN ONCE_REWRITE_TAC[GSYM SUMMABLE_RESTRICT] THEN
  MATCH_MP_TAC SUMMABLE_IFF_EVENTUALLY THEN
  FIRST_ASSUM(MP_TAC o ISPEC `\x:num.x` o MATCH_MP UPPER_BOUND_FINITE_SET) THEN
  DISCH_THEN(X_CHOOSE_THEN `N:num` MP_TAC) THEN REWRITE_TAC[IN_UNIV] THEN
  DISCH_TAC THEN EXISTS_TAC `N + 1` THEN
  REWRITE_TAC[ARITH_RULE `N + 1 <= n <=> ~(n <= N)`] THEN ASM SET_TAC[]);;


let SUMMABLE_EQ_COFINITE = 
prove
 (`!f s t. FINITE((s DIFF t) UNION (t DIFF s)) /\ summable s f
           ==> summable t f`,

  MESON_TAC[SUMMABLE_IFF_COFINITE]);;


let SUMMABLE_FROM_ELSEWHERE = 
prove
 (`!f m n. summable (from m) f ==> summable (from n) f`,

  REPEAT GEN_TAC THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] SUMMABLE_EQ_COFINITE) THEN
  MATCH_MP_TAC FINITE_SUBSET THEN EXISTS_TAC `0..(m+n)` THEN
  SIMP_TAC[FINITE_NUMSEG; SUBSET; IN_NUMSEG; IN_UNION; IN_DIFF; IN_FROM] THEN
  ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* Uniform vesion of Cauchy criterion.                                       *)
(* ------------------------------------------------------------------------- *)


let SERIES_CAUCHY_UNIFORM = 
prove
 (`!P f:A->num->real^N k.
        (?l. !e. &0 < e
                 ==> ?N. !n x. N <= n /\ P x
                               ==> dist(vsum(k INTER (0..n)) (f x),
                                        l x) < e) <=>
        (!e. &0 < e ==> ?N. !m n x. N <= m /\ P x
                                    ==> norm(vsum(k INTER (m..n)) (f x)) < e)`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[sums; UNIFORMLY_CONVERGENT_EQ_CAUCHY; cauchy] THEN
  ONCE_REWRITE_TAC[MESON[]
   `(!m n:num y. N <= m /\ N <= n /\ P y ==> Q m n y) <=>
    (!y. P y ==> !m n. N <= m /\ N <= n ==> Q m n y)`] THEN
  REWRITE_TAC[SEQUENCE_CAUCHY_WLOG] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
  SIMP_TAC[dist; VSUM_DIFF_LEMMA; NORM_VSUM_TRIVIAL_LEMMA] THEN
  REWRITE_TAC[GE; TAUT `a ==> b \/ c <=> a /\ ~b ==> c`] THEN
  REWRITE_TAC[NOT_LT; ARITH_RULE
   `(N <= m /\ N <= n /\ m <= n) /\ m + 1 <= n <=>
    N + 1 <= m + 1 /\ m + 1 <= n`] THEN
  AP_TERM_TAC THEN REWRITE_TAC[FUN_EQ_THM] THEN X_GEN_TAC `e:real` THEN
  ASM_CASES_TAC `&0 < e` THEN ASM_REWRITE_TAC[] THEN
  EQ_TAC THEN DISCH_THEN(X_CHOOSE_TAC `N:num`) THENL
   [EXISTS_TAC `N + 1`; EXISTS_TAC `N:num`] THEN
  REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[ARITH_RULE `N + 1 <= m + 1 ==> N <= m + 1`] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:A`) THEN ASM_REWRITE_TAC[] THEN
  DISCH_THEN(MP_TAC o SPECL [`m - 1`; `n:num`]) THEN
  SUBGOAL_THEN `m - 1 + 1 = m` SUBST_ALL_TAC THENL
   [ALL_TAC; ANTS_TAC THEN SIMP_TAC[]] THEN
  ASM_ARITH_TAC);;

(* ------------------------------------------------------------------------- *)
(* So trivially, terms of a convergent series go to zero.                    *)
(* ------------------------------------------------------------------------- *)


let SERIES_GOESTOZERO = 
prove
 (`!s x. summable s x
         ==> !e. &0 < e
                 ==> eventually (\n. n IN s ==> norm(x n) < e) sequentially`,

  REPEAT GEN_TAC THEN REWRITE_TAC[summable; SERIES_CAUCHY] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[EVENTUALLY_SEQUENTIALLY] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN DISCH_TAC THEN
  X_GEN_TAC `n:num` THEN REPEAT STRIP_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`n:num`; `n:num`]) THEN
  ASM_SIMP_TAC[NUMSEG_SING; GE; SET_RULE `n IN s ==> s INTER {n} = {n}`] THEN
  REWRITE_TAC[VSUM_SING]);;


let SUMMABLE_IMP_TOZERO = 
prove
 (`!f:num->real^N k.
       summable k f
       ==> ((\n. if n IN k then f(n) else vec 0) --> vec 0) sequentially`,

  REPEAT GEN_TAC THEN GEN_REWRITE_TAC LAND_CONV [GSYM SUMMABLE_RESTRICT] THEN
  REWRITE_TAC[summable; LIM_SEQUENTIALLY; INTER_UNIV; sums] THEN
  DISCH_THEN(X_CHOOSE_TAC `l:real^N`) THEN X_GEN_TAC `e:real` THEN
  DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[REAL_HALF; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `N:num` THEN DISCH_TAC THEN EXISTS_TAC `N + 1` THEN
  X_GEN_TAC `n:num` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(fun th ->
    MP_TAC(SPEC `n - 1` th) THEN MP_TAC(SPEC `n:num` th)) THEN
  ASM_SIMP_TAC[ARITH_RULE `N + 1 <= n ==> N <= n /\ N <= n - 1`] THEN
  ABBREV_TAC `m = n - 1` THEN
  SUBGOAL_THEN `n = SUC m` SUBST1_TAC THENL
   [ASM_ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[VSUM_CLAUSES_NUMSEG; LE_0] THEN
  REWRITE_TAC[NORM_ARITH `dist(x,vec 0) = norm x`] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[NORM_0] THEN CONV_TAC NORM_ARITH);;


let SUMMABLE_IMP_BOUNDED = 
prove
 (`!f:num->real^N k. summable k f ==> bounded (IMAGE f k)`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP SUMMABLE_IMP_TOZERO) THEN
  DISCH_THEN(MP_TAC o MATCH_MP CONVERGENT_IMP_BOUNDED) THEN
  REWRITE_TAC[BOUNDED_POS; FORALL_IN_IMAGE; IN_UNIV] THEN
  MATCH_MP_TAC MONO_EXISTS THEN MESON_TAC[REAL_LT_IMP_LE; NORM_0]);;


let SUMMABLE_IMP_SUMS_BOUNDED = 
prove
 (`!f:num->real^N k.
       summable (from k) f ==> bounded { vsum(k..n) f | n IN (:num) }`,

  REWRITE_TAC[summable; sums; LEFT_IMP_EXISTS_THM] THEN REPEAT GEN_TAC THEN
  DISCH_THEN(MP_TAC o MATCH_MP CONVERGENT_IMP_BOUNDED) THEN
  REWRITE_TAC[FROM_INTER_NUMSEG; SIMPLE_IMAGE]);;

(* ------------------------------------------------------------------------- *)
(* Comparison test.                                                          *)
(* ------------------------------------------------------------------------- *)


let SERIES_COMPARISON = 
prove
 (`!f g s. (?l. ((lift o g) sums l) s) /\
           (?N. !n. n >= N /\ n IN s ==> norm(f n) <= g n)
           ==> ?l:real^N. (f sums l) s`,

  REPEAT GEN_TAC THEN REWRITE_TAC[SERIES_CAUCHY] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC (X_CHOOSE_TAC `N1:num`)) THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_TAC `N2:num`) THEN
  EXISTS_TAC `N1 + N2:num` THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN DISCH_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `norm (vsum (s INTER (m .. n)) (lift o g))` THEN CONJ_TAC THENL
   [SIMP_TAC[GSYM LIFT_SUM; FINITE_INTER_NUMSEG; NORM_LIFT] THEN
    MATCH_MP_TAC(REAL_ARITH `x <= a ==> x <= abs(a)`) THEN
    MATCH_MP_TAC VSUM_NORM_LE THEN
    REWRITE_TAC[FINITE_INTER_NUMSEG; IN_INTER; IN_NUMSEG] THEN
    ASM_MESON_TAC[ARITH_RULE `m >= N1 + N2:num /\ m <= x ==> x >= N1`];
    ASM_MESON_TAC[ARITH_RULE `m >= N1 + N2:num ==> m >= N2`]]);;


let SUMMABLE_COMPARISON = 
prove
 (`!f g s. summable s (lift o g) /\
           (?N. !n. n >= N /\ n IN s ==> norm(f n) <= g n)
           ==> summable s f`,

  REWRITE_TAC[summable; SERIES_COMPARISON]);;


let SERIES_LIFT_ABSCONV_IMP_CONV = 
prove
 (`!x:num->real^N k. summable k (\n. lift(norm(x n))) ==> summable k x`,

  REWRITE_TAC[summable] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SERIES_COMPARISON THEN
  EXISTS_TAC `\n:num. norm(x n:real^N)` THEN
  ASM_REWRITE_TAC[o_DEF; REAL_LE_REFL] THEN ASM_MESON_TAC[]);;


let SUMMABLE_SUBSET_ABSCONV = 
prove
 (`!x:num->real^N s t.
        summable s (\n. lift(norm(x n))) /\ t SUBSET s
        ==> summable t (\n. lift(norm(x n)))`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUMMABLE_SUBSET THEN
  EXISTS_TAC `s:num->bool` THEN ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[summable] THEN MATCH_MP_TAC SERIES_COMPARISON THEN
  EXISTS_TAC `\n:num. norm(x n:real^N)` THEN
  ASM_REWRITE_TAC[o_DEF; GSYM summable] THEN
  EXISTS_TAC `0` THEN REPEAT STRIP_TAC THEN COND_CASES_TAC THEN
  REWRITE_TAC[REAL_LE_REFL; NORM_LIFT; REAL_ABS_NORM; NORM_0; NORM_POS_LE]);;


let SERIES_COMPARISON_BOUND = 
prove
 (`!f:num->real^N g s a.
        (g sums a) s /\ (!i. i IN s ==> norm(f i) <= drop(g i))
        ==> ?l. (f sums l) s /\ norm(l) <= drop a`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:num->real^N`; `drop o (g:num->real^1)`; `s:num->bool`]
        SUMMABLE_COMPARISON) THEN
  REWRITE_TAC[o_DEF; LIFT_DROP; GE; ETA_AX; summable] THEN
  ANTS_TAC THENL [ASM_MESON_TAC[]; MATCH_MP_TAC MONO_EXISTS] THEN
  X_GEN_TAC `l:real^N` THEN DISCH_TAC THEN ASM_REWRITE_TAC[] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[FROM_0; INTER_UNIV; sums]) THEN
  MATCH_MP_TAC SERIES_BOUND THEN MAP_EVERY EXISTS_TAC
   [`f:num->real^N`; `drop o (g:num->real^1)`; `s:num->bool`] THEN
  ASM_REWRITE_TAC[sums; o_DEF; LIFT_DROP; ETA_AX]);;

(* ------------------------------------------------------------------------- *)
(* Uniform version of comparison test.                                       *)
(* ------------------------------------------------------------------------- *)


let SERIES_COMPARISON_UNIFORM = 
prove
 (`!f g P s. (?l. ((lift o g) sums l) s) /\
             (?N. !n x. N <= n /\ n IN s /\ P x ==> norm(f x n) <= g n)
             ==> ?l:A->real^N.
                    !e. &0 < e
                        ==> ?N. !n x. N <= n /\ P x
                                      ==> dist(vsum(s INTER (0..n)) (f x),
                                               l x) < e`,

  REPEAT GEN_TAC THEN SIMP_TAC[GE; SERIES_CAUCHY; SERIES_CAUCHY_UNIFORM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC (X_CHOOSE_TAC `N1:num`)) THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `e:real` THEN
  MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_TAC `N2:num`) THEN
  EXISTS_TAC `N1 + N2:num` THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`; `x:A`] THEN DISCH_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `norm (vsum (s INTER (m .. n)) (lift o g))` THEN CONJ_TAC THENL
   [SIMP_TAC[GSYM LIFT_SUM; FINITE_INTER_NUMSEG; NORM_LIFT] THEN
    MATCH_MP_TAC(REAL_ARITH `x <= a ==> x <= abs(a)`) THEN
    MATCH_MP_TAC VSUM_NORM_LE THEN
    REWRITE_TAC[FINITE_INTER_NUMSEG; IN_INTER; IN_NUMSEG] THEN
    ASM_MESON_TAC[ARITH_RULE `N1 + N2:num <= m /\ m <= x ==> N1 <= x`];
    ASM_MESON_TAC[ARITH_RULE `N1 + N2:num <= m ==> N2 <= m`]]);;

(* ------------------------------------------------------------------------- *)
(* Ratio test.                                                               *)
(* ------------------------------------------------------------------------- *)


let SERIES_RATIO = 
prove
 (`!c a s N.
      c < &1 /\
      (!n. n >= N ==> norm(a(SUC n)) <= c * norm(a(n)))
      ==> ?l:real^N. (a sums l) s`,

  REWRITE_TAC[GE] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC SERIES_COMPARISON THEN
  DISJ_CASES_TAC(REAL_ARITH `c <= &0 \/ &0 < c`) THENL
   [EXISTS_TAC `\n:num. &0` THEN REWRITE_TAC[o_DEF; LIFT_NUM] THEN
    CONJ_TAC THENL [MESON_TAC[SERIES_0]; ALL_TAC] THEN
    EXISTS_TAC `N + 1` THEN REWRITE_TAC[GE] THEN REPEAT STRIP_TAC THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC `c * norm(a(n - 1):real^N)` THEN
    CONJ_TAC THENL
     [ASM_MESON_TAC[ARITH_RULE `N + 1 <= n ==> SUC(n - 1) = n /\ N <= n - 1`];
      ALL_TAC] THEN
    MATCH_MP_TAC(REAL_ARITH `&0 <= --c * x ==> c * x <= &0`) THEN
    MATCH_MP_TAC REAL_LE_MUL THEN REWRITE_TAC[NORM_POS_LE] THEN
    UNDISCH_TAC `c <= &0` THEN REAL_ARITH_TAC;
    ASSUME_TAC(MATCH_MP REAL_LT_IMP_LE (ASSUME `&0 < c`))] THEN
  EXISTS_TAC `\n. norm(a(N):real^N) * c pow (n - N)` THEN
  REWRITE_TAC[] THEN CONJ_TAC THENL
   [ALL_TAC;
    EXISTS_TAC `N:num` THEN
    SIMP_TAC[GE; LE_EXISTS; IMP_CONJ; ADD_SUB2; LEFT_IMP_EXISTS_THM] THEN
    SUBGOAL_THEN `!d:num. norm(a(N + d):real^N) <= norm(a N) * c pow d`
     (fun th -> MESON_TAC[th]) THEN INDUCT_TAC THEN
    REWRITE_TAC[ADD_CLAUSES; real_pow; REAL_MUL_RID; REAL_LE_REFL] THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN
    EXISTS_TAC `c * norm((a:num->real^N) (N + d))` THEN
    ASM_SIMP_TAC[LE_ADD] THEN ASM_MESON_TAC[REAL_LE_LMUL; REAL_MUL_AC]] THEN
  GEN_REWRITE_TAC I [SERIES_CAUCHY] THEN X_GEN_TAC `e:real` THEN
  SIMP_TAC[GSYM LIFT_SUM; FINITE_INTER; NORM_LIFT; FINITE_NUMSEG] THEN
  DISCH_TAC THEN SIMP_TAC[SUM_LMUL; FINITE_INTER; FINITE_NUMSEG] THEN
  ASM_CASES_TAC `(a:num->real^N) N = vec 0` THENL
   [ASM_REWRITE_TAC[NORM_0; REAL_MUL_LZERO; REAL_ABS_NUM]; ALL_TAC] THEN
  MP_TAC(SPECL [`c:real`; `((&1 - c) * e) / norm((a:num->real^N) N)`]
               REAL_ARCH_POW_INV) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_LT_MUL; REAL_SUB_LT; NORM_POS_LT; GE] THEN
  DISCH_THEN(X_CHOOSE_TAC `M:num`) THEN EXISTS_TAC `N + M:num` THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN DISCH_TAC THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `abs(norm((a:num->real^N) N) *
                  sum(m..n) (\i. c pow (i - N)))` THEN
  CONJ_TAC THENL
   [REWRITE_TAC[REAL_ABS_MUL] THEN MATCH_MP_TAC REAL_LE_LMUL THEN
    REWRITE_TAC[REAL_ABS_POS] THEN
    MATCH_MP_TAC(REAL_ARITH `&0 <= x /\ x <= y ==> abs x <= abs y`) THEN
    ASM_SIMP_TAC[SUM_POS_LE; FINITE_INTER_NUMSEG; REAL_POW_LE] THEN
    MATCH_MP_TAC SUM_SUBSET THEN ASM_SIMP_TAC[REAL_POW_LE] THEN
    REWRITE_TAC[FINITE_INTER_NUMSEG; FINITE_NUMSEG] THEN
    REWRITE_TAC[IN_INTER; IN_DIFF] THEN MESON_TAC[];
    ALL_TAC] THEN
  REWRITE_TAC[REAL_ABS_MUL; REAL_ABS_NORM] THEN
  DISJ_CASES_TAC(ARITH_RULE `n:num < m \/ m <= n`) THENL
   [ASM_SIMP_TAC[SUM_TRIV_NUMSEG; REAL_ABS_NUM; REAL_MUL_RZERO]; ALL_TAC] THEN
  SUBGOAL_THEN `m = 0 + m /\ n = (n - m) + m` (CONJUNCTS_THEN SUBST1_TAC) THENL
   [UNDISCH_TAC `m:num <= n` THEN ARITH_TAC; ALL_TAC] THEN
  REWRITE_TAC[SUM_OFFSET] THEN UNDISCH_TAC `N + M:num <= m` THEN
  SIMP_TAC[LE_EXISTS] THEN DISCH_THEN(X_CHOOSE_THEN `d:num` SUBST_ALL_TAC) THEN
  REWRITE_TAC[ARITH_RULE `(i + (N + M) + d) - N:num = (M + d) + i`] THEN
  ONCE_REWRITE_TAC[REAL_POW_ADD] THEN REWRITE_TAC[SUM_LMUL; SUM_GP] THEN
  ASM_SIMP_TAC[LT; REAL_LT_IMP_NE] THEN ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ; NORM_POS_LT; REAL_ABS_MUL] THEN
  REWRITE_TAC[REAL_ABS_POW] THEN ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN
  ASM_SIMP_TAC[GSYM REAL_LT_RDIV_EQ; REAL_ABS_DIV; REAL_POW_LT; REAL_ARITH
   `&0 < c /\ c < &1 ==> &0 < abs c /\ &0 < abs(&1 - c)`; REAL_LT_LDIV_EQ] THEN
  MATCH_MP_TAC(REAL_ARITH
   `&0 < x /\ x <= &1 /\ &1 <= e ==> abs(c pow 0 - x) < e`) THEN
  ASM_SIMP_TAC[REAL_POW_LT; REAL_POW_1_LE; REAL_LT_IMP_LE] THEN
  ASM_SIMP_TAC[REAL_ARITH `c < &1 ==> x * abs(&1 - c) = (&1 - c) * x`] THEN
  REWRITE_TAC[real_div; REAL_INV_MUL; REAL_POW_ADD; REAL_MUL_ASSOC] THEN
  REWRITE_TAC[REAL_ARITH
   `(((a * b) * c) * d) * e = (e * ((a * b) * c)) * d`] THEN
  ASM_SIMP_TAC[GSYM real_div; REAL_LE_RDIV_EQ; REAL_POW_LT; REAL_MUL_LID;
               REAL_ARITH `&0 < c ==> abs c = c`] THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
   `xm < e ==> &0 <= (d - &1) * e ==> xm <= d * e`)) THEN
  MATCH_MP_TAC REAL_LE_MUL THEN CONJ_TAC THENL
   [REWRITE_TAC[REAL_SUB_LE; GSYM REAL_POW_INV] THEN
    MATCH_MP_TAC REAL_POW_LE_1 THEN
    MATCH_MP_TAC REAL_INV_1_LE THEN ASM_SIMP_TAC[REAL_LT_IMP_LE];
    MATCH_MP_TAC REAL_LT_IMP_LE THEN
    ASM_SIMP_TAC[REAL_SUB_LT; REAL_LT_MUL; REAL_LT_DIV; NORM_POS_LT]]);;

(* ------------------------------------------------------------------------- *)
(* Ostensibly weaker versions of the boundedness of partial sums.            *)
(* ------------------------------------------------------------------------- *)


let BOUNDED_PARTIAL_SUMS = 
prove
 (`!f:num->real^N k.
        bounded { vsum(k..n) f | n IN (:num) }
        ==> bounded { vsum(m..n) f | m IN (:num) /\ n IN (:num) }`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `bounded { vsum(0..n) f:real^N | n IN (:num) }` MP_TAC THENL
   [FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
    REWRITE_TAC[bounded] THEN
    REWRITE_TAC[SIMPLE_IMAGE; FORALL_IN_IMAGE; IN_UNIV] THEN
    DISCH_THEN(X_CHOOSE_THEN `B:real` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `sum { i:num | i < k} (\i. norm(f i:real^N)) + B` THEN
    X_GEN_TAC `i:num` THEN ASM_CASES_TAC `i:num < k` THENL
     [MATCH_MP_TAC(REAL_ARITH
       `!y. x <= y /\ y <= a /\ &0 < b ==> x <= a + b`) THEN
      EXISTS_TAC `sum (0..i) (\i. norm(f i:real^N))` THEN
      ASM_SIMP_TAC[VSUM_NORM; FINITE_NUMSEG] THEN
      MATCH_MP_TAC SUM_SUBSET THEN
      REWRITE_TAC[FINITE_NUMSEG; FINITE_NUMSEG_LT; NORM_POS_LE] THEN
      REWRITE_TAC[IN_DIFF; IN_NUMSEG; IN_ELIM_THM] THEN ASM_ARITH_TAC;
      ALL_TAC] THEN
    ASM_CASES_TAC `k = 0` THENL
     [FIRST_X_ASSUM SUBST_ALL_TAC THEN MATCH_MP_TAC(REAL_ARITH
       `x <= B /\ &0 <= b ==> x <= b + B`) THEN
      ASM_SIMP_TAC[SUM_POS_LE; FINITE_NUMSEG_LT; NORM_POS_LE];
      ALL_TAC] THEN
    MP_TAC(ISPECL [`f:num->real^N`; `0`; `k:num`; `i:num`]
      VSUM_COMBINE_L) THEN
    ANTS_TAC THENL [ASM_ARITH_TAC; ALL_TAC] THEN
    DISCH_THEN(SUBST1_TAC o SYM) THEN ASM_REWRITE_TAC[NUMSEG_LT] THEN
    MATCH_MP_TAC(NORM_ARITH
     `norm(x) <= a /\ norm(y) <= b ==> norm(x + y) <= a + b`) THEN
    ASM_SIMP_TAC[VSUM_NORM; FINITE_NUMSEG];
    ALL_TAC] THEN
  DISCH_THEN(fun th ->
    MP_TAC(MATCH_MP BOUNDED_DIFFS (W CONJ th)) THEN MP_TAC th) THEN
  REWRITE_TAC[IMP_IMP; GSYM BOUNDED_UNION] THEN
  MATCH_MP_TAC(REWRITE_RULE[TAUT `a /\ b ==> c <=> b ==> a ==> c`]
        BOUNDED_SUBSET) THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_UNION; LEFT_IMP_EXISTS_THM; IN_UNIV] THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `m:num`; `n:num`] THEN
  DISCH_THEN SUBST1_TAC THEN
  ASM_CASES_TAC `m = 0` THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
  ASM_CASES_TAC `n:num < m` THENL
   [DISJ2_TAC THEN REPEAT(EXISTS_TAC `vsum(0..0) (f:num->real^N)`) THEN
    ASM_SIMP_TAC[VSUM_TRIV_NUMSEG; VECTOR_SUB_REFL] THEN MESON_TAC[];
    ALL_TAC] THEN
  DISJ2_TAC THEN MAP_EVERY EXISTS_TAC
   [`vsum(0..n) (f:num->real^N)`; `vsum(0..(m-1)) (f:num->real^N)`] THEN
  CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPECL [`f:num->real^N`; `0`; `m:num`; `n:num`]
      VSUM_COMBINE_L) THEN
  ANTS_TAC THENL [ASM_ARITH_TAC; VECTOR_ARITH_TAC]);;

(* ------------------------------------------------------------------------- *)
(* General Dirichlet convergence test (could make this uniform on a set).    *)
(* ------------------------------------------------------------------------- *)


let SUMMABLE_BILINEAR_PARTIAL_PRE = 
prove
 (`!f g h:real^M->real^N->real^P l k.
        bilinear h /\
        ((\n. h (f(n + 1)) (g(n))) --> l) sequentially /\
        summable (from k) (\n. h (f(n + 1) - f(n)) (g(n)))
        ==> summable (from k) (\n. h (f n) (g(n) - g(n - 1)))`,

  REPEAT GEN_TAC THEN
  REWRITE_TAC[summable; sums; FROM_INTER_NUMSEG] THEN
  REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  FIRST_ASSUM(fun th ->
   REWRITE_TAC[MATCH_MP BILINEAR_VSUM_PARTIAL_PRE th]) THEN
  DISCH_THEN(X_CHOOSE_TAC `l':real^P`) THEN
  EXISTS_TAC `l - (h:real^M->real^N->real^P) (f k) (g(k - 1)) - l'` THEN
  REWRITE_TAC[LIM_CASES_SEQUENTIALLY] THEN
  REPEAT(MATCH_MP_TAC LIM_SUB THEN ASM_REWRITE_TAC[LIM_CONST]));;


let SERIES_DIRICHLET_BILINEAR = 
prove
 (`!f g h:real^M->real^N->real^P k m p l.
        bilinear h /\
        bounded { vsum (m..n) f | n IN (:num)} /\
        summable (from p) (\n. lift(norm(g(n + 1) - g(n)))) /\
        ((\n. h (g(n + 1)) (vsum(1..n) f)) --> l) sequentially
        ==> summable (from k) (\n. h (g n) (f n))`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SUMMABLE_FROM_ELSEWHERE THEN
  EXISTS_TAC `1` THEN
  FIRST_X_ASSUM(ASSUME_TAC o MATCH_MP BOUNDED_PARTIAL_SUMS) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
  SIMP_TAC[IN_ELIM_THM; IN_UNIV; LEFT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[MESON[] `(!x a b. x = f a b ==> p a b) <=> (!a b. p a b)`] THEN
  X_GEN_TAC `B:real` THEN STRIP_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP BILINEAR_BOUNDED_POS) THEN
  DISCH_THEN(X_CHOOSE_THEN `C:real` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC SUMMABLE_EQ THEN
  EXISTS_TAC `\n. (h:real^M->real^N->real^P)
                  (g n) (vsum (1..n) f - vsum (1..n-1) f)` THEN
  SIMP_TAC[IN_FROM; GSYM NUMSEG_RREC] THEN
  SIMP_TAC[VSUM_CLAUSES; FINITE_NUMSEG; IN_NUMSEG;
           ARITH_RULE `1 <= n ==> ~(n <= n - 1)`] THEN
  CONJ_TAC THENL
   [REPEAT STRIP_TAC THEN ASM_SIMP_TAC[BILINEAR_RADD; BILINEAR_RSUB] THEN
    VECTOR_ARITH_TAC;
    ALL_TAC] THEN
  MATCH_MP_TAC SUMMABLE_FROM_ELSEWHERE THEN EXISTS_TAC `p:num` THEN
  MP_TAC(ISPECL [`g:num->real^M`; `\n. vsum(1..n) f:real^N`;
                 `h:real^M->real^N->real^P`; `l:real^P`; `p:num`]
         SUMMABLE_BILINEAR_PARTIAL_PRE) THEN
  REWRITE_TAC[] THEN DISCH_THEN MATCH_MP_TAC THEN
  ASM_REWRITE_TAC[] THEN
  SUBGOAL_THEN
    `summable (from p) (lift o (\n. C * B * norm(g(n + 1) - g(n):real^M)))`
  MP_TAC THENL [ASM_SIMP_TAC[o_DEF; LIFT_CMUL; SUMMABLE_CMUL]; ALL_TAC] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] SUMMABLE_COMPARISON) THEN
  EXISTS_TAC `0` THEN REWRITE_TAC[IN_FROM; GE; LE_0] THEN
  REPEAT STRIP_TAC THEN MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC
   `C * norm(g(n + 1) - g(n):real^M) * norm(vsum (1..n) f:real^N)` THEN
  ASM_SIMP_TAC[REAL_LE_LMUL_EQ] THEN
  GEN_REWRITE_TAC RAND_CONV [REAL_MUL_SYM] THEN
  ASM_SIMP_TAC[REAL_LE_LMUL; NORM_POS_LE]);;


let SERIES_DIRICHLET = 
prove
 (`!f:num->real^N g N k m.
        bounded { vsum (m..n) f | n IN (:num)} /\
        (!n. N <= n ==> g(n + 1) <= g(n)) /\
        ((lift o g) --> vec 0) sequentially
        ==> summable (from k) (\n. g(n) % f(n))`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`f:num->real^N`; `lift o (g:num->real)`;
                 `\x y:real^N. drop x % y`] SERIES_DIRICHLET_BILINEAR) THEN
  REWRITE_TAC[o_THM; LIFT_DROP] THEN DISCH_THEN MATCH_MP_TAC THEN
  MAP_EVERY EXISTS_TAC [`m:num`; `N:num`; `vec 0:real^N`] THEN CONJ_TAC THENL
   [REWRITE_TAC[bilinear; linear; DROP_ADD; DROP_CMUL] THEN
    REPEAT STRIP_TAC THEN VECTOR_ARITH_TAC;
    ALL_TAC] THEN
  ASM_REWRITE_TAC[GSYM LIFT_SUB; NORM_LIFT] THEN
  FIRST_ASSUM(MP_TAC o SPEC `1` o MATCH_MP SEQ_OFFSET) THEN
  REWRITE_TAC[o_THM] THEN DISCH_TAC THEN CONJ_TAC THENL
   [MATCH_MP_TAC SUMMABLE_EQ_EVENTUALLY THEN
    EXISTS_TAC `\n. lift(g(n) - g(n + 1))` THEN REWRITE_TAC[] THEN
    CONJ_TAC THENL
     [ASM_MESON_TAC[REAL_ARITH `b <= a ==> abs(b - a) = a - b`];
      REWRITE_TAC[summable; sums; FROM_INTER_NUMSEG; VSUM_DIFFS; LIFT_SUB] THEN
      REWRITE_TAC[LIM_CASES_SEQUENTIALLY] THEN
      EXISTS_TAC `lift(g(N:num)) - vec 0` THEN
      MATCH_MP_TAC LIM_SUB THEN ASM_REWRITE_TAC[LIM_CONST]];
    MATCH_MP_TAC LIM_NULL_VMUL_BOUNDED THEN ASM_REWRITE_TAC[o_DEF] THEN
    REWRITE_TAC[EVENTUALLY_SEQUENTIALLY] THEN
    FIRST_X_ASSUM(ASSUME_TAC o MATCH_MP BOUNDED_PARTIAL_SUMS) THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [BOUNDED_POS]) THEN
    SIMP_TAC[IN_ELIM_THM; IN_UNIV] THEN MESON_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Rearranging absolutely convergent series.                                 *)
(* ------------------------------------------------------------------------- *)


let SERIES_INJECTIVE_IMAGE_STRONG = 
prove
 (`!x:num->real^N s f.
        summable (IMAGE f s) (\n. lift(norm(x n))) /\
        (!m n. m IN s /\ n IN s /\ f m = f n ==> m = n)
        ==> ((\n. vsum (IMAGE f s INTER (0..n)) x -
                  vsum (s INTER (0..n)) (x o f)) --> vec 0)
            sequentially`,

  
let lemma = prove
   (`!f:A->real^N s t.
          FINITE s /\ FINITE t
          ==> vsum s f - vsum t f = vsum (s DIFF t) f - vsum (t DIFF s) f`,
    REPEAT STRIP_TAC THEN
    ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s DIFF (s INTER t)`] THEN
    ASM_SIMP_TAC[VSUM_DIFF; INTER_SUBSET] THEN
    REWRITE_TAC[INTER_COMM] THEN VECTOR_ARITH_TAC) in
  REPEAT STRIP_TAC THEN REWRITE_TAC[LIM_SEQUENTIALLY] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [SUMMABLE_CAUCHY]) THEN
  SIMP_TAC[VSUM_REAL; FINITE_INTER; FINITE_NUMSEG] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [o_DEF] THEN
  REWRITE_TAC[NORM_LIFT; LIFT_DROP] THEN
  SIMP_TAC[real_abs; SUM_POS_LE; NORM_POS_LE; FINITE_INTER; FINITE_NUMSEG] THEN
  DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN
  ASM_REWRITE_TAC[dist; GE; VECTOR_SUB_RZERO; REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_THEN `N:num` STRIP_ASSUME_TAC) THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [INJECTIVE_ON_LEFT_INVERSE]) THEN
  DISCH_THEN(X_CHOOSE_TAC `g:num->num`) THEN
  MP_TAC(ISPECL [`g:num->num`; `0..N`] UPPER_BOUND_FINITE_SET) THEN
  REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG; LE_0] THEN
  DISCH_THEN(X_CHOOSE_TAC `P:num`) THEN
  EXISTS_TAC `MAX N P` THEN X_GEN_TAC `n:num` THEN
  SIMP_TAC[ARITH_RULE `MAX a b <= c <=> a <= c /\ b <= c`] THEN DISCH_TAC THEN
  W(MP_TAC o PART_MATCH (rand o rand) VSUM_IMAGE o rand o
    rand o lhand o snd) THEN
  ANTS_TAC THENL
   [ASM_MESON_TAC[FINITE_INTER; FINITE_NUMSEG; IN_INTER];
    DISCH_THEN(SUBST1_TAC o SYM)] THEN
  W(MP_TAC o PART_MATCH (lhand o rand) lemma o rand o lhand o snd) THEN
  SIMP_TAC[FINITE_INTER; FINITE_IMAGE; FINITE_NUMSEG] THEN
  DISCH_THEN SUBST1_TAC THEN MATCH_MP_TAC(NORM_ARITH
   `norm a < e / &2 /\ norm b < e / &2 ==> norm(a - b:real^N) < e`) THEN
  CONJ_TAC THEN
  W(MP_TAC o PART_MATCH (lhand o rand) VSUM_NORM o lhand o snd) THEN
  SIMP_TAC[FINITE_DIFF; FINITE_IMAGE; FINITE_INTER; FINITE_NUMSEG] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] REAL_LET_TRANS) THEN
  MATCH_MP_TAC REAL_LET_TRANS THENL
   [EXISTS_TAC
     `sum(IMAGE (f:num->num) s INTER (N..n)) (\i. norm(x i :real^N))` THEN
    ASM_SIMP_TAC[LE_REFL] THEN MATCH_MP_TAC SUM_SUBSET_SIMPLE THEN
    SIMP_TAC[NORM_POS_LE; FINITE_INTER; FINITE_NUMSEG] THEN
    MATCH_MP_TAC(SET_RULE
     `(!x. x IN s /\ f(x) IN n /\ ~(x IN m) ==> f x IN t)
      ==> (IMAGE f s INTER n) DIFF (IMAGE f (s INTER m)) SUBSET
          IMAGE f s INTER t`) THEN
    ASM_SIMP_TAC[IN_NUMSEG; LE_0; NOT_LE] THEN
    X_GEN_TAC `i:num` THEN STRIP_TAC THEN
    MATCH_MP_TAC LT_IMP_LE THEN ONCE_REWRITE_TAC[GSYM NOT_LE] THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o GEN_REWRITE_RULE BINDER_CONV
     [GSYM CONTRAPOS_THM]) THEN
    ASM_SIMP_TAC[] THEN ASM_ARITH_TAC;
    MP_TAC(ISPECL [`f:num->num`; `0..n`] UPPER_BOUND_FINITE_SET) THEN
    REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG; LE_0] THEN
    DISCH_THEN(X_CHOOSE_TAC `p:num`) THEN
    EXISTS_TAC
     `sum(IMAGE (f:num->num) s INTER (N..p)) (\i. norm(x i :real^N))` THEN
    ASM_SIMP_TAC[LE_REFL] THEN MATCH_MP_TAC SUM_SUBSET_SIMPLE THEN
    SIMP_TAC[NORM_POS_LE; FINITE_INTER; FINITE_NUMSEG] THEN
    MATCH_MP_TAC(SET_RULE
     `(!x. x IN s /\ x IN n /\ ~(f x IN m) ==> f x IN t)
      ==> (IMAGE f (s INTER n) DIFF (IMAGE f s) INTER m) SUBSET
          (IMAGE f s INTER t)`) THEN
    ASM_SIMP_TAC[IN_NUMSEG; LE_0] THEN ASM_ARITH_TAC]);;


let SERIES_INJECTIVE_IMAGE = 
prove
 (`!x:num->real^N s f l.
        summable (IMAGE f s) (\n. lift(norm(x n))) /\
        (!m n. m IN s /\ n IN s /\ f m = f n ==> m = n)
        ==> (((x o f) sums l) s <=> (x sums l) (IMAGE f s))`,

  REPEAT STRIP_TAC THEN CONV_TAC SYM_CONV THEN REWRITE_TAC[sums] THEN
  MATCH_MP_TAC LIM_TRANSFORM_EQ THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC SERIES_INJECTIVE_IMAGE_STRONG THEN
  ASM_REWRITE_TAC[]);;


let SERIES_REARRANGE_EQ = 
prove
 (`!x:num->real^N s p l.
        summable s (\n. lift(norm(x n))) /\ p permutes s
        ==> (((x o p) sums l) s <=> (x sums l) s)`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`x:num->real^N`; `s:num->bool`; `p:num->num`; `l:real^N`]
        SERIES_INJECTIVE_IMAGE) THEN
  ASM_SIMP_TAC[PERMUTES_IMAGE] THEN
  ASM_MESON_TAC[PERMUTES_INJECTIVE]);;


let SERIES_REARRANGE = 
prove
 (`!x:num->real^N s p l.
        summable s (\n. lift(norm(x n))) /\ p permutes s /\ (x sums l) s
        ==> ((x o p) sums l) s`,

  MESON_TAC[SERIES_REARRANGE_EQ]);;


let SUMMABLE_REARRANGE = 
prove
 (`!x s p.
        summable s (\n. lift(norm(x n))) /\ p permutes s
        ==> summable s (x o p)`,

(* ------------------------------------------------------------------------- *)
(* Banach fixed point theorem (not really topological...)                    *)
(* ------------------------------------------------------------------------- *)


let BANACH_FIX = 
prove
 (`!f s c. complete s /\ ~(s = {}) /\
           &0 <= c /\ c < &1 /\
           (IMAGE f s) SUBSET s /\
           (!x y. x IN s /\ y IN s ==> dist(f(x),f(y)) <= c * dist(x,y))
           ==> ?!x:real^N. x IN s /\ (f x = x)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[EXISTS_UNIQUE_THM] THEN CONJ_TAC THENL
   [ALL_TAC;
    MAP_EVERY X_GEN_TAC [`x:real^N`; `y:real^N`] THEN STRIP_TAC THEN
    SUBGOAL_THEN `dist((f:real^N->real^N) x,f y) <= c * dist(x,y)` MP_TAC THENL
     [ASM_MESON_TAC[]; ALL_TAC] THEN
    ASM_REWRITE_TAC[REAL_ARITH `a <= c * a <=> &0 <= --a * (&1 - c)`] THEN
    ASM_SIMP_TAC[GSYM REAL_LE_LDIV_EQ; REAL_SUB_LT; real_div] THEN
    REWRITE_TAC[REAL_MUL_LZERO; REAL_ARITH `&0 <= --x <=> ~(&0 < x)`] THEN
    MESON_TAC[DIST_POS_LT]] THEN
  STRIP_ASSUME_TAC(prove_recursive_functions_exist num_RECURSION
    `(z 0 = @x:real^N. x IN s) /\ (!n. z(SUC n) = f(z n))`) THEN
  SUBGOAL_THEN `!n. (z:num->real^N) n IN s` ASSUME_TAC THENL
   [INDUCT_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_MESON_TAC[MEMBER_NOT_EMPTY; SUBSET; IN_IMAGE];
    ALL_TAC] THEN
  UNDISCH_THEN `z 0 = @x:real^N. x IN s` (K ALL_TAC) THEN
  SUBGOAL_THEN `?x:real^N. x IN s /\ (z --> x) sequentially` MP_TAC THENL
   [ALL_TAC;
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN
    STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    ABBREV_TAC `e = dist(f(a:real^N),a)` THEN
    SUBGOAL_THEN `~(&0 < e)` (fun th -> ASM_MESON_TAC[th; DIST_POS_LT]) THEN
    DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [LIM_SEQUENTIALLY]) THEN
    DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN
    ASM_REWRITE_TAC[REAL_HALF] THEN DISCH_THEN(X_CHOOSE_TAC `N:num`) THEN
    SUBGOAL_THEN
     `dist(f(z N),a:real^N) < e / &2 /\ dist(f(z(N:num)),f(a)) < e / &2`
     (fun th -> ASM_MESON_TAC[th; DIST_TRIANGLE_HALF_R; REAL_LT_REFL]) THEN
    CONJ_TAC THENL [ASM_MESON_TAC[ARITH_RULE `N <= SUC N`]; ALL_TAC] THEN
    MATCH_MP_TAC REAL_LET_TRANS THEN
    EXISTS_TAC `c * dist((z:num->real^N) N,a)` THEN ASM_SIMP_TAC[] THEN
    MATCH_MP_TAC(REAL_ARITH `x < y /\ c * x <= &1 * x ==> c * x < y`) THEN
    ASM_SIMP_TAC[LE_REFL; REAL_LE_RMUL; DIST_POS_LE; REAL_LT_IMP_LE]] THEN
  FIRST_ASSUM(MATCH_MP_TAC o GEN_REWRITE_RULE I [complete]) THEN
  ASM_REWRITE_TAC[CAUCHY] THEN
  SUBGOAL_THEN `!n. dist(z(n):real^N,z(SUC n)) <= c pow n * dist(z(0),z(1))`
  ASSUME_TAC THENL
   [INDUCT_TAC THEN
    REWRITE_TAC[real_pow; ARITH; REAL_MUL_LID; REAL_LE_REFL] THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN
    EXISTS_TAC `c * dist(z(n):real^N,z(SUC n))` THEN
    CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
    REWRITE_TAC[GSYM REAL_MUL_ASSOC] THEN ASM_SIMP_TAC[REAL_LE_LMUL];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!m n:num. (&1 - c) * dist(z(m):real^N,z(m+n))
                <= c pow m * dist(z(0),z(1)) * (&1 - c pow n)`
  ASSUME_TAC THENL
   [GEN_TAC THEN INDUCT_TAC THENL
     [REWRITE_TAC[ADD_CLAUSES; DIST_REFL; REAL_MUL_RZERO] THEN
      MATCH_MP_TAC REAL_LE_MUL THEN
      ASM_SIMP_TAC[REAL_LE_MUL; REAL_POW_LE; DIST_POS_LE; REAL_SUB_LE;
                   REAL_POW_1_LE; REAL_LT_IMP_LE];
      ALL_TAC] THEN
    MATCH_MP_TAC REAL_LE_TRANS THEN EXISTS_TAC
    `(&1 - c) * (dist(z m:real^N,z(m + n)) + dist(z(m + n),z(m + SUC n)))` THEN
    ASM_SIMP_TAC[REAL_LE_LMUL; REAL_SUB_LE; REAL_LT_IMP_LE; DIST_TRIANGLE] THEN
    FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
      `c * x <= y ==> c * x' + y <= y' ==> c * (x + x') <= y'`)) THEN
    REWRITE_TAC[REAL_ARITH
     `q + a * b * (&1 - x) <= a * b * (&1 - y) <=> q <= a * b * (x - y)`] THEN
    REWRITE_TAC[ADD_CLAUSES; real_pow] THEN
    REWRITE_TAC[REAL_ARITH `a * b * (d - c * d) = (&1 - c) * a * d * b`] THEN
    MATCH_MP_TAC REAL_LE_LMUL THEN
    ASM_SIMP_TAC[REAL_SUB_LE; REAL_LT_IMP_LE] THEN
    REWRITE_TAC[GSYM REAL_POW_ADD; REAL_MUL_ASSOC] THEN ASM_MESON_TAC[];
    ALL_TAC] THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  ASM_CASES_TAC `(z:num->real^N) 0 = z 1` THENL
   [FIRST_X_ASSUM SUBST_ALL_TAC THEN EXISTS_TAC `0` THEN
    REWRITE_TAC[GE; LE_0] THEN X_GEN_TAC `n:num` THEN
    FIRST_X_ASSUM(MP_TAC o SPECL [`0`; `n:num`]) THEN
    REWRITE_TAC[ADD_CLAUSES; DIST_REFL; REAL_MUL_LZERO; REAL_MUL_RZERO] THEN
    ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
    ASM_CASES_TAC `(z:num->real^N) 0 = z n` THEN
    ASM_REWRITE_TAC[DIST_REFL; REAL_NOT_LE] THEN
    ASM_SIMP_TAC[REAL_LT_MUL; DIST_POS_LT; REAL_SUB_LT];
    ALL_TAC] THEN
  MP_TAC(SPECL [`c:real`; `e * (&1 - c) / dist((z:num->real^N) 0,z 1)`]
   REAL_ARCH_POW_INV) THEN
  ASM_SIMP_TAC[REAL_LT_MUL; REAL_LT_DIV; REAL_SUB_LT; DIST_POS_LT] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  REWRITE_TAC[real_div; GE; REAL_MUL_ASSOC] THEN
  ASM_SIMP_TAC[REAL_LT_RDIV_EQ; GSYM real_div; DIST_POS_LT] THEN
  ASM_SIMP_TAC[GSYM REAL_LT_LDIV_EQ; REAL_SUB_LT] THEN DISCH_TAC THEN
  REWRITE_TAC[LE_EXISTS; LEFT_IMP_EXISTS_THM] THEN
  GEN_TAC THEN X_GEN_TAC `d:num` THEN DISCH_THEN SUBST_ALL_TAC THEN
  ONCE_REWRITE_TAC[DIST_SYM] THEN
  FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP(REAL_ARITH
    `d < e ==> x <= d ==> x < e`)) THEN
  ASM_SIMP_TAC[REAL_LE_RDIV_EQ; REAL_SUB_LT] THEN
  FIRST_X_ASSUM(MP_TAC o SPECL [`N:num`; `d:num`]) THEN
  MATCH_MP_TAC(REAL_ARITH
  `(c * d) * e <= (c * d) * &1 ==> x * y <= c * d * e ==> y * x <= c * d`) THEN
  MATCH_MP_TAC REAL_LE_LMUL THEN
  ASM_SIMP_TAC[REAL_LE_MUL; REAL_POW_LE; DIST_POS_LE; REAL_ARITH
   `&0 <= x ==> &1 - x <= &1`]);;

(* ------------------------------------------------------------------------- *)
(* Edelstein fixed point theorem.                                            *)
(* ------------------------------------------------------------------------- *)


let EDELSTEIN_FIX = 
prove
 (`!f s. compact s /\ ~(s = {}) /\ (IMAGE f s) SUBSET s /\
         (!x y. x IN s /\ y IN s /\ ~(x = y) ==> dist(f(x),f(y)) < dist(x,y))
         ==> ?!x:real^N. x IN s /\ f x = x`,

  MAP_EVERY X_GEN_TAC [`g:real^N->real^N`; `s:real^N->bool`] THEN
  REPEAT STRIP_TAC THEN REWRITE_TAC[EXISTS_UNIQUE_THM] THEN CONJ_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[REAL_LT_REFL]] THEN
  SUBGOAL_THEN
   `!x y. x IN s /\ y IN s ==> dist((g:real^N->real^N)(x),g(y)) <= dist(x,y)`
  ASSUME_TAC THENL
   [REPEAT STRIP_TAC THEN ASM_CASES_TAC `x:real^N = y` THEN
    ASM_SIMP_TAC[DIST_REFL; REAL_LE_LT];
    ALL_TAC] THEN
  ASM_CASES_TAC `?x:real^N. x IN s /\ ~(g x = x)` THENL
   [ALL_TAC; ASM SET_TAC[]] THEN
  FIRST_X_ASSUM(X_CHOOSE_THEN `x:real^N` STRIP_ASSUME_TAC) THEN
  ABBREV_TAC `y = (g:real^N->real^N) x` THEN
  SUBGOAL_THEN `(y:real^N) IN s` ASSUME_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP COMPACT_PCROSS o W CONJ) THEN
  REWRITE_TAC[compact; PCROSS] THEN
  (STRIP_ASSUME_TAC o prove_general_recursive_function_exists)
    `?f:num->real^N->real^N.
        (!z. f 0 z = z) /\ (!z n. f (SUC n) z = g(f n z))` THEN
  SUBGOAL_THEN `!n z. z IN s ==> (f:num->real^N->real^N) n z IN s`
  STRIP_ASSUME_TAC THENL [INDUCT_TAC THEN ASM SET_TAC[]; ALL_TAC] THEN
  SUBGOAL_THEN
   `!m n w z. m <= n /\ w IN s /\ z IN s
              ==> dist((f:num->real^N->real^N) n w,f n z) <= dist(f m w,f m z)`
  ASSUME_TAC THENL
   [REWRITE_TAC[RIGHT_FORALL_IMP_THM; IMP_CONJ] THEN
    MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN
    RULE_ASSUM_TAC(REWRITE_RULE[SUBSET; FORALL_IN_IMAGE]) THEN
    ASM_SIMP_TAC[REAL_LE_REFL] THEN MESON_TAC[REAL_LE_TRANS];
    ALL_TAC] THEN
  DISCH_THEN(MP_TAC o SPEC
   `\n:num. pastecart (f n (x:real^N)) (f n y:real^N)`) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; REWRITE_TAC[LEFT_IMP_EXISTS_THM]] THEN
  MAP_EVERY X_GEN_TAC [`l:real^(N,N)finite_sum`; `s:num->num`] THEN
  REWRITE_TAC[o_DEF; IN_ELIM_THM] THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC STRIP_ASSUME_TAC) THEN
  REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
  MAP_EVERY X_GEN_TAC [`a:real^N`; `b:real^N`] THEN
  DISCH_THEN(CONJUNCTS_THEN2 STRIP_ASSUME_TAC SUBST_ALL_TAC) THEN
  SUBGOAL_THEN
   `(\x:real^(N,N)finite_sum. fstcart x) continuous_on UNIV /\
    (\x:real^(N,N)finite_sum. sndcart x) continuous_on UNIV`
  MP_TAC THENL
   [CONJ_TAC THEN MATCH_MP_TAC LINEAR_CONTINUOUS_ON THEN
    REWRITE_TAC[ETA_AX; LINEAR_FSTCART; LINEAR_SNDCART];
    ALL_TAC] THEN
  REWRITE_TAC[CONTINUOUS_ON_SEQUENTIALLY; IN_UNIV] THEN
  DISCH_THEN(CONJUNCTS_THEN(fun th -> FIRST_ASSUM(MP_TAC o MATCH_MP th))) THEN
  REWRITE_TAC[o_DEF; FSTCART_PASTECART; SNDCART_PASTECART; IMP_IMP] THEN
  ONCE_REWRITE_TAC[CONJ_SYM] THEN
  DISCH_THEN(fun th -> CONJUNCTS_THEN2 (LABEL_TAC "A") (LABEL_TAC "B") th THEN
    MP_TAC(MATCH_MP LIM_SUB th)) THEN
  REWRITE_TAC[] THEN DISCH_THEN(LABEL_TAC "AB") THEN
  SUBGOAL_THEN
   `!n. dist(a:real^N,b) <= dist((f:num->real^N->real^N) n x,f n y)`
  STRIP_ASSUME_TAC THENL
   [X_GEN_TAC `N:num` THEN REWRITE_TAC[GSYM REAL_NOT_LT] THEN
    ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN DISCH_TAC THEN
    USE_THEN "AB" (MP_TAC o REWRITE_RULE[LIM_SEQUENTIALLY]) THEN
    DISCH_THEN(fun th -> FIRST_X_ASSUM(MP_TAC o MATCH_MP th)) THEN
    REWRITE_TAC[NOT_EXISTS_THM] THEN X_GEN_TAC `M:num` THEN
    DISCH_THEN(MP_TAC o SPEC `M + N:num`) THEN REWRITE_TAC[LE_ADD] THEN
    MATCH_MP_TAC(NORM_ARITH
     `dist(fx,fy) <= dist(x,y)
      ==> ~(dist(fx - fy,a - b) < dist(a,b) - dist(x,y))`) THEN
    FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[] THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `M + N:num` o MATCH_MP MONOTONE_BIGGER) THEN
    ARITH_TAC;
    ALL_TAC] THEN
  SUBGOAL_THEN `b:real^N = a` SUBST_ALL_TAC THENL
   [MATCH_MP_TAC(TAUT `(~p ==> F) ==> p`) THEN DISCH_TAC THEN
    ABBREV_TAC `e = dist(a,b) - dist((g:real^N->real^N) a,g b)` THEN
    SUBGOAL_THEN `&0 < e` ASSUME_TAC THENL
     [ASM_MESON_TAC[REAL_SUB_LT]; ALL_TAC] THEN
    SUBGOAL_THEN
     `?n. dist((f:num->real^N->real^N) n x,a) < e / &2 /\
          dist(f n y,b) < e / &2`
    STRIP_ASSUME_TAC THENL
     [MAP_EVERY (fun s -> USE_THEN s (MP_TAC o SPEC `e / &2` o
        REWRITE_RULE[LIM_SEQUENTIALLY])) ["A";
 "B"] THEN
      ASM_REWRITE_TAC[REAL_HALF] THEN
      DISCH_THEN(X_CHOOSE_TAC `M:num`) THEN
      DISCH_THEN(X_CHOOSE_TAC `N:num`) THEN
      EXISTS_TAC `(s:num->num) (M + N)` THEN
      CONJ_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN ARITH_TAC;
      ALL_TAC] THEN
    SUBGOAL_THEN `dist(f (SUC n) x,(g:real^N->real^N) a) +
                  dist((f:num->real^N->real^N) (SUC n) y,g b) < e`
    MP_TAC THENL
     [ASM_REWRITE_TAC[] THEN
      MATCH_MP_TAC(REAL_ARITH `x < e / &2 /\ y < e / &2 ==> x + y < e`) THEN
      CONJ_TAC THEN FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP (REAL_ARITH
       `dist(x,y) < e
        ==> dist(g x,g y) <= dist(x,y) ==> dist(g x,g y) < e`)) THEN
      ASM_SIMP_TAC[];
      ALL_TAC] THEN
    MP_TAC(SPEC `SUC n` (ASSUME
    `!n. dist (a:real^N,b) <=
         dist ((f:num->real^N->real^N) n x,f n y)`)) THEN
    EXPAND_TAC "e" THEN NORM_ARITH_TAC;
    ALL_TAC] THEN
  EXISTS_TAC `a:real^N` THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC(ISPEC `sequentially` LIM_UNIQUE) THEN
  EXISTS_TAC `\n:num. (f:num->real^N->real^N) (SUC(s n)) x` THEN
  REWRITE_TAC[TRIVIAL_LIMIT_SEQUENTIALLY] THEN CONJ_TAC THENL
   [ASM_REWRITE_TAC[] THEN
    SUBGOAL_THEN `(g:real^N->real^N) continuous_on s` MP_TAC THENL
     [REWRITE_TAC[continuous_on] THEN ASM_MESON_TAC[REAL_LET_TRANS];
      ALL_TAC] THEN
    REWRITE_TAC[CONTINUOUS_ON_SEQUENTIALLY; o_DEF] THEN
    DISCH_THEN MATCH_MP_TAC THEN ASM_SIMP_TAC[];
    SUBGOAL_THEN `!n. (f:num->real^N->real^N) (SUC n) x = f n y`
     (fun th -> ASM_SIMP_TAC[th]) THEN
    INDUCT_TAC THEN ASM_REWRITE_TAC[]]);;

(* ------------------------------------------------------------------------- *)
(* Dini's theorem.                                                           *)
(* ------------------------------------------------------------------------- *)


let DINI = 
prove
 (`!f:num->real^N->real^1 g s.
        compact s /\ (!n. (f n) continuous_on s) /\ g continuous_on s /\
        (!x. x IN s ==> ((\n. (f n x)) --> g x) sequentially) /\
        (!n x. x IN s ==> drop(f n x) <= drop(f (n + 1) x))
        ==> !e. &0 < e
                ==> eventually (\n. !x. x IN s ==> norm(f n x - g x) < e)
                               sequentially`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `!x:real^N m n:num. x IN s /\ m <= n ==> drop(f m x) <= drop(f n x)`
  ASSUME_TAC THENL
   [GEN_TAC THEN ASM_CASES_TAC `(x:real^N) IN s` THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN ASM_SIMP_TAC[ADD1] THEN
    REAL_ARITH_TAC;
    ALL_TAC] THEN
  SUBGOAL_THEN `!n:num x:real^N. x IN s ==> drop(f n x) <= drop(g x)`
  ASSUME_TAC THENL
   [REPEAT STRIP_TAC THEN
    MATCH_MP_TAC(ISPEC `sequentially` LIM_DROP_LE) THEN
    EXISTS_TAC `\m:num. (f:num->real^N->real^1) n x` THEN
    EXISTS_TAC `\m:num. (f:num->real^N->real^1) m x` THEN
    ASM_SIMP_TAC[LIM_CONST; TRIVIAL_LIMIT_SEQUENTIALLY] THEN
    REWRITE_TAC[EVENTUALLY_SEQUENTIALLY] THEN ASM_MESON_TAC[];
    ALL_TAC] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[LIM_SEQUENTIALLY; dist]) THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I
   [COMPACT_EQ_HEINE_BOREL_SUBTOPOLOGY]) THEN
  DISCH_THEN(MP_TAC o SPEC
   `IMAGE (\n. { x | x IN s /\ norm((f:num->real^N->real^1) n x - g x) < e})
          (:num)`) THEN
  REWRITE_TAC[FORALL_IN_IMAGE; IN_UNIV] THEN
  ONCE_REWRITE_TAC[TAUT `p /\ q /\ r <=> q /\ p /\ r`] THEN
  REWRITE_TAC[EXISTS_FINITE_SUBSET_IMAGE; SUBSET_UNION; UNIONS_IMAGE] THEN
  REWRITE_TAC[IN_UNIV; IN_ELIM_THM; EVENTUALLY_SEQUENTIALLY] THEN
  SIMP_TAC[SUBSET; IN_UNIV; IN_ELIM_THM] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[LE_REFL]] THEN
    X_GEN_TAC `n:num` THEN REWRITE_TAC[GSYM IN_BALL_0] THEN
    MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE THEN
    ASM_SIMP_TAC[OPEN_BALL; CONTINUOUS_ON_SUB; ETA_AX];

    DISCH_THEN(X_CHOOSE_THEN `k:num->bool` (CONJUNCTS_THEN2
     (MP_TAC o SPEC `\n:num. n` o MATCH_MP UPPER_BOUND_FINITE_SET)
     (LABEL_TAC "*"))) THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
    REWRITE_TAC[] THEN STRIP_TAC THEN X_GEN_TAC `n:num` THEN
    DISCH_TAC THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    REMOVE_THEN "*" (MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `m:num` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
    REWRITE_TAC[NORM_REAL; GSYM drop; DROP_SUB] THEN MATCH_MP_TAC(REAL_ARITH
     `m <= n /\ n <= g ==> abs(m - g) < e ==> abs(n - g) < e`) THEN
    ASM_MESON_TAC[LE_TRANS]]);;

(* ------------------------------------------------------------------------- *)
(* Closest point of a (closed) set to a point.                               *)
(* ------------------------------------------------------------------------- *)


let closest_point = new_definition
 `closest_point s a = @x. x IN s /\ !y. y IN s ==> dist(a,x) <= dist(a,y)`;;


let CLOSEST_POINT_EXISTS = 
prove
 (`!s a. closed s /\ ~(s = {})
         ==> (closest_point s a) IN s /\
             !y. y IN s ==> dist(a,closest_point s a) <= dist(a,y)`,

  REWRITE_TAC[closest_point] THEN CONV_TAC(ONCE_DEPTH_CONV SELECT_CONV) THEN
  REWRITE_TAC[DISTANCE_ATTAINS_INF]);;


let CLOSEST_POINT_IN_SET = 
prove
 (`!s a. closed s /\ ~(s = {}) ==> (closest_point s a) IN s`,

  MESON_TAC[CLOSEST_POINT_EXISTS]);;


let CLOSEST_POINT_LE = 
prove
 (`!s a x. closed s /\ x IN s ==> dist(a,closest_point s a) <= dist(a,x)`,


let CLOSEST_POINT_SELF = 
prove
 (`!s x:real^N. x IN s ==> closest_point s x = x`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[closest_point] THEN
  MATCH_MP_TAC SELECT_UNIQUE THEN REWRITE_TAC[] THEN GEN_TAC THEN EQ_TAC THENL
   [STRIP_TAC THEN FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN
    ASM_SIMP_TAC[DIST_LE_0; DIST_REFL];
    STRIP_TAC THEN ASM_REWRITE_TAC[DIST_REFL; DIST_POS_LE]]);;


let CLOSEST_POINT_REFL = 
prove
 (`!s x:real^N. closed s /\ ~(s = {}) ==> (closest_point s x = x <=> x IN s)`,


let DIST_CLOSEST_POINT_LIPSCHITZ = 
prove
 (`!s x y:real^N.
        closed s /\ ~(s = {})
        ==> abs(dist(x,closest_point s x) - dist(y,closest_point s y))
            <= dist(x,y)`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN
  FIRST_ASSUM(MP_TAC o MATCH_MP CLOSEST_POINT_EXISTS) THEN
  DISCH_THEN(fun th ->
    CONJUNCTS_THEN2 ASSUME_TAC
     (MP_TAC o SPEC `closest_point s (y:real^N)`) (SPEC `x:real^N` th) THEN
    CONJUNCTS_THEN2 ASSUME_TAC
     (MP_TAC o SPEC `closest_point s (x:real^N)`) (SPEC `y:real^N` th)) THEN
  ASM_REWRITE_TAC[] THEN NORM_ARITH_TAC);;


let CONTINUOUS_AT_DIST_CLOSEST_POINT = 
prove
 (`!s x:real^N.
        closed s /\ ~(s = {})
        ==> (\x. lift(dist(x,closest_point s x))) continuous (at x)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[continuous_at; DIST_LIFT] THEN
  ASM_MESON_TAC[DIST_CLOSEST_POINT_LIPSCHITZ; REAL_LET_TRANS]);;


let CONTINUOUS_ON_DIST_CLOSEST_POINT = 
prove
 (`!s t. closed s /\ ~(s = {})
         ==> (\x. lift(dist(x,closest_point s x))) continuous_on t`,


let UNIFORMLY_CONTINUOUS_ON_DIST_CLOSEST_POINT = 
prove
 (`!s t:real^N->bool.
        closed s /\ ~(s = {})
        ==> (\x. lift(dist(x,closest_point s x))) uniformly_continuous_on t`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[uniformly_continuous_on; DIST_LIFT] THEN
  ASM_MESON_TAC[DIST_CLOSEST_POINT_LIPSCHITZ; REAL_LET_TRANS]);;


let SEGMENT_TO_CLOSEST_POINT = 
prove
 (`!s a:real^N.
        closed s /\ ~(s = {})
        ==> segment(a,closest_point s a) INTER s = {}`,

  REPEAT STRIP_TAC THEN
  REWRITE_TAC[SET_RULE `s INTER t = {} <=> !x. x IN s ==> ~(x IN t)`] THEN
  GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP DIST_IN_OPEN_SEGMENT) THEN
  MATCH_MP_TAC(TAUT `(r ==> ~p) ==> p /\ q ==> ~r`) THEN
  ASM_MESON_TAC[CLOSEST_POINT_EXISTS; REAL_NOT_LT; DIST_SYM]);;


let SEGMENT_TO_POINT_EXISTS = 
prove
 (`!s a:real^N.
        closed s /\ ~(s = {}) ==> ?b. b IN s /\ segment(a,b) INTER s = {}`,


let CLOSEST_POINT_IN_INTERIOR = 
prove
 (`!s x:real^N.
        closed s /\ ~(s = {})
        ==> ((closest_point s x) IN interior s <=> x IN interior s)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `(x:real^N) IN s` THEN
  ASM_SIMP_TAC[CLOSEST_POINT_SELF] THEN
  MATCH_MP_TAC(TAUT `~q /\ ~p ==> (p <=> q)`) THEN
  CONJ_TAC THENL [ASM_MESON_TAC[INTERIOR_SUBSET; SUBSET]; STRIP_TAC] THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [IN_INTERIOR_CBALL]) THEN
  DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
  SUBGOAL_THEN `closest_point s (x:real^N) IN s` ASSUME_TAC THENL
   [ASM_MESON_TAC[INTERIOR_SUBSET; SUBSET]; ALL_TAC] THEN
  SUBGOAL_THEN `~(closest_point s (x:real^N) = x)` ASSUME_TAC THENL
   [ASM_MESON_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `x:real^N`;
   `closest_point s x -
    (min (&1) (e / norm(closest_point s x - x))) %
    (closest_point s x - x):real^N`]
    CLOSEST_POINT_LE) THEN
  ASM_REWRITE_TAC[dist; NOT_IMP; VECTOR_ARITH
   `x - (y - e % (y - x)):real^N = (&1 - e) % (x - y)`] THEN
  CONJ_TAC THENL
   [FIRST_X_ASSUM(MATCH_MP_TAC o GEN_REWRITE_RULE I [SUBSET]) THEN
    REWRITE_TAC[IN_CBALL; NORM_ARITH `dist(a:real^N,a - x) = norm x`] THEN
    REWRITE_TAC[NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM] THEN
    ASM_SIMP_TAC[GSYM REAL_LE_RDIV_EQ; NORM_POS_LT; VECTOR_SUB_EQ] THEN
    MATCH_MP_TAC(REAL_ARITH `&0 <= a ==> abs(min (&1) a) <= a`) THEN
    ASM_SIMP_TAC[REAL_LT_IMP_LE; REAL_LE_DIV; NORM_POS_LE];
    REWRITE_TAC[NORM_MUL; REAL_ARITH
     `~(n <= a * n) <=> &0 < (&1 - a) * n`] THEN
    MATCH_MP_TAC REAL_LT_MUL THEN
    ASM_SIMP_TAC[NORM_POS_LT; VECTOR_SUB_EQ] THEN
    MATCH_MP_TAC(REAL_ARITH
     `&0 < e /\ e <= &1 ==> &0 < &1 - abs(&1 - e)`) THEN
    REWRITE_TAC[REAL_MIN_LE; REAL_LT_MIN; REAL_LT_01; REAL_LE_REFL] THEN
    ASM_SIMP_TAC[REAL_LT_DIV; NORM_POS_LT; VECTOR_SUB_EQ]]);;


let CLOSEST_POINT_IN_FRONTIER = 
prove
 (`!s x:real^N.
        closed s /\ ~(s = {}) /\ ~(x IN interior s)
        ==> (closest_point s x) IN frontier s`,

  SIMP_TAC[frontier; IN_DIFF; CLOSEST_POINT_IN_INTERIOR] THEN
  SIMP_TAC[CLOSEST_POINT_IN_SET; CLOSURE_CLOSED]);;

(* ------------------------------------------------------------------------- *)
(* More general infimum of distance between two sets.                        *)
(* ------------------------------------------------------------------------- *)


let setdist = new_definition
 `setdist(s,t) =
        if s = {} \/ t = {} then &0
        else inf {dist(x,y) | x IN s /\ y IN t}`;;


let SETDIST_EMPTY = 
prove
 (`(!t. setdist({},t) = &0) /\ (!s. setdist(s,{}) = &0)`,

  REWRITE_TAC[setdist]);;


let SETDIST_POS_LE = 
prove
 (`!s t. &0 <= setdist(s,t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[setdist] THEN
  COND_CASES_TAC THEN REWRITE_TAC[REAL_LE_REFL] THEN
  MATCH_MP_TAC REAL_LE_INF THEN
  REWRITE_TAC[FORALL_IN_GSPEC; DIST_POS_LE] THEN ASM SET_TAC[]);;


let REAL_LE_SETDIST = 
prove
  (`!s t:real^N->bool d.
        ~(s = {}) /\ ~(t = {}) /\
        (!x y. x IN s /\ y IN t ==> d <= dist(x,y))
        ==> d <= setdist(s,t)`,

  REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[setdist] THEN
  MP_TAC(ISPEC `{dist(x:real^N,y) | x IN s /\ y IN t}` INF) THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ASM SET_TAC[]; MESON_TAC[DIST_POS_LE]]; ALL_TAC] THEN
  ASM_MESON_TAC[]);;


let SETDIST_LE_DIST = 
prove
 (`!s t x y:real^N. x IN s /\ y IN t ==> setdist(s,t) <= dist(x,y)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[setdist] THEN
  COND_CASES_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPEC `{dist(x:real^N,y) | x IN s /\ y IN t}` INF) THEN
  REWRITE_TAC[FORALL_IN_GSPEC] THEN ANTS_TAC THENL
   [CONJ_TAC THENL [ASM SET_TAC[]; MESON_TAC[DIST_POS_LE]]; ALL_TAC] THEN
  ASM_MESON_TAC[]);;


let REAL_LE_SETDIST_EQ = 
prove
 (`!d s t:real^N->bool.
        d <= setdist(s,t) <=>
        (!x y. x IN s /\ y IN t ==> d <= dist(x,y)) /\
        (s = {} \/ t = {} ==> d <= &0)`,

  REPEAT GEN_TAC THEN MAP_EVERY ASM_CASES_TAC
   [`s:real^N->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; NOT_IN_EMPTY] THEN
  ASM_MESON_TAC[REAL_LE_SETDIST; SETDIST_LE_DIST; REAL_LE_TRANS]);;


let REAL_SETDIST_LT_EXISTS = 
prove
 (`!s t:real^N->bool b.
        ~(s = {}) /\ ~(t = {}) /\ setdist(s,t) < b
        ==> ?x y. x IN s /\ y IN t /\ dist(x,y) < b`,

  REWRITE_TAC[GSYM REAL_NOT_LE; REAL_LE_SETDIST_EQ] THEN MESON_TAC[]);;


let SETDIST_REFL = 
prove
 (`!s:real^N->bool. setdist(s,s) = &0`,

  GEN_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM; SETDIST_POS_LE] THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [ASM_REWRITE_TAC[setdist; REAL_LE_REFL]; ALL_TAC] THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; MEMBER_NOT_EMPTY; DIST_REFL]);;


let SETDIST_SYM = 
prove
 (`!s t. setdist(s,t) = setdist(t,s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[setdist; DISJ_SYM] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
  AP_TERM_TAC THEN REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN
  MESON_TAC[DIST_SYM]);;


let SETDIST_TRIANGLE = 
prove
 (`!s a t:real^N->bool.
        setdist(s,t) <= setdist(s,{a}) + setdist({a},t)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; REAL_ADD_LID; SETDIST_POS_LE] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; REAL_ADD_RID; SETDIST_POS_LE] THEN
  ONCE_REWRITE_TAC[GSYM REAL_LE_SUB_RADD] THEN
  MATCH_MP_TAC REAL_LE_SETDIST THEN
  ASM_REWRITE_TAC[NOT_INSERT_EMPTY; IN_SING; IMP_CONJ;
                  RIGHT_FORALL_IMP_THM; FORALL_UNWIND_THM2] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  ONCE_REWRITE_TAC[REAL_ARITH `x - y <= z <=> x - z <= y`] THEN
  MATCH_MP_TAC REAL_LE_SETDIST THEN
  ASM_REWRITE_TAC[NOT_INSERT_EMPTY; IN_SING; IMP_CONJ;
                  RIGHT_FORALL_IMP_THM; FORALL_UNWIND_THM2] THEN
  X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
  REWRITE_TAC[REAL_LE_SUB_RADD] THEN MATCH_MP_TAC REAL_LE_TRANS THEN
  EXISTS_TAC `dist(x:real^N,y)` THEN
  ASM_SIMP_TAC[SETDIST_LE_DIST] THEN CONV_TAC NORM_ARITH);;


let SETDIST_SINGS = 
prove
 (`!x y. setdist({x},{y}) = dist(x,y)`,

  REWRITE_TAC[setdist; NOT_INSERT_EMPTY] THEN
  REWRITE_TAC[SET_RULE `{f x y | x IN {a} /\ y IN {b}} = {f a b}`] THEN
  SIMP_TAC[INF_INSERT_FINITE; FINITE_EMPTY]);;


let SETDIST_LIPSCHITZ = 
prove
 (`!s t x y:real^N. abs(setdist({x},s) - setdist({y},s)) <= dist(x,y)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM SETDIST_SINGS] THEN
  REWRITE_TAC[REAL_ARITH
   `abs(x - y) <= z <=> x <= z + y /\ y <= z + x`] THEN
  MESON_TAC[SETDIST_TRIANGLE; SETDIST_SYM]);;


let CONTINUOUS_AT_LIFT_SETDIST = 
prove
 (`!s x:real^N. (\y. lift(setdist({y},s))) continuous (at x)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[continuous_at; DIST_LIFT] THEN
  ASM_MESON_TAC[SETDIST_LIPSCHITZ; REAL_LET_TRANS]);;


let CONTINUOUS_ON_LIFT_SETDIST = 
prove
 (`!s t:real^N->bool. (\y. lift(setdist({y},s))) continuous_on t`,


let UNIFORMLY_CONTINUOUS_ON_LIFT_SETDIST = 
prove
 (`!s t:real^N->bool.
         (\y. lift(setdist({y},s))) uniformly_continuous_on t`,

  REPEAT GEN_TAC THEN REWRITE_TAC[uniformly_continuous_on; DIST_LIFT] THEN
  ASM_MESON_TAC[SETDIST_LIPSCHITZ; REAL_LET_TRANS]);;


let SETDIST_DIFFERENCES = 
prove
 (`!s t. setdist(s,t) = setdist({vec 0},{x - y:real^N | x IN s /\ y IN t})`,

  REPEAT GEN_TAC THEN REWRITE_TAC[setdist; NOT_INSERT_EMPTY;
     SET_RULE `{f x y | x IN s /\ y IN t} = {} <=> s = {} \/ t = {}`] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN AP_TERM_TAC THEN
  REWRITE_TAC[EXTENSION; IN_ELIM_THM; IN_SING] THEN
  REWRITE_TAC[GSYM CONJ_ASSOC; RIGHT_EXISTS_AND_THM; UNWIND_THM2; DIST_0] THEN
  REWRITE_TAC[dist] THEN MESON_TAC[]);;


let SETDIST_SUBSET_RIGHT = 
prove
 (`!s t u:real^N->bool.
    ~(t = {}) /\ t SUBSET u ==> setdist(s,u) <= setdist(s,t)`,

  REPEAT STRIP_TAC THEN
  MAP_EVERY ASM_CASES_TAC [`s:real^N->bool = {}`; `u:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; SETDIST_POS_LE; REAL_LE_REFL] THEN
  ASM_REWRITE_TAC[setdist] THEN MATCH_MP_TAC REAL_LE_INF_SUBSET THEN
  ASM_REWRITE_TAC[FORALL_IN_GSPEC; SUBSET] THEN
  REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
  MESON_TAC[DIST_POS_LE]);;


let SETDIST_SUBSET_LEFT = 
prove
 (`!s t u:real^N->bool.
    ~(s = {}) /\ s SUBSET t ==> setdist(t,u) <= setdist(s,u)`,


let SETDIST_CLOSURE = 
prove
 (`(!s t:real^N->bool. setdist(closure s,t) = setdist(s,t)) /\
   (!s t:real^N->bool. setdist(s,closure t) = setdist(s,t))`,

  GEN_REWRITE_TAC RAND_CONV [SWAP_FORALL_THM] THEN
  GEN_REWRITE_TAC (RAND_CONV o ONCE_DEPTH_CONV) [SETDIST_SYM] THEN
  REWRITE_TAC[] THEN
  REWRITE_TAC[MESON[REAL_LE_ANTISYM]
   `x:real = y <=> !d. d <= x <=> d <= y`] THEN
  REPEAT GEN_TAC THEN REWRITE_TAC[REAL_LE_SETDIST_EQ] THEN
  MAP_EVERY ASM_CASES_TAC [`s:real^N->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[CLOSURE_EQ_EMPTY; CLOSURE_EMPTY; NOT_IN_EMPTY] THEN
  MATCH_MP_TAC(SET_RULE
   `s SUBSET c /\
    (!y. Q y /\ (!x. x IN s ==> P x y) ==> (!x. x IN c ==> P x y))
   ==> ((!x y. x IN c /\ Q y ==> P x y) <=>
        (!x y. x IN s /\ Q y ==> P x y))`) THEN
  REWRITE_TAC[CLOSURE_SUBSET] THEN GEN_TAC THEN STRIP_TAC THEN
  MATCH_MP_TAC CONTINUOUS_GE_ON_CLOSURE THEN
  ASM_REWRITE_TAC[o_DEF; dist] THEN
  MATCH_MP_TAC CONTINUOUS_ON_LIFT_NORM_COMPOSE THEN
  SIMP_TAC[CONTINUOUS_ON_SUB; CONTINUOUS_ON_CONST; CONTINUOUS_ON_ID]);;


let SETDIST_COMPACT_CLOSED = 
prove
 (`!s t:real^N->bool.
        compact s /\ closed t /\ ~(s = {}) /\ ~(t = {})
        ==> ?x y. x IN s /\ y IN t /\ dist(x,y) = setdist(s,t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN
  MATCH_MP_TAC(MESON[]
   `(!x y. P x /\ Q y ==> S x y) /\ (?x y. P x /\ Q y /\ R x y)
    ==> ?x y. P x /\ Q y /\ R x y /\ S x y`) THEN
  SIMP_TAC[SETDIST_LE_DIST] THEN
  ASM_REWRITE_TAC[REAL_LE_SETDIST_EQ] THEN
  MP_TAC(ISPECL [`{x - y:real^N | x IN s /\ y IN t}`; `vec 0:real^N`]
        DISTANCE_ATTAINS_INF) THEN
  ASM_SIMP_TAC[COMPACT_CLOSED_DIFFERENCES; EXISTS_IN_GSPEC; FORALL_IN_GSPEC;
               DIST_0; GSYM CONJ_ASSOC] THEN
  REWRITE_TAC[dist] THEN DISCH_THEN MATCH_MP_TAC THEN ASM SET_TAC[]);;


let SETDIST_CLOSED_COMPACT = 
prove
 (`!s t:real^N->bool.
        closed s /\ compact t /\ ~(s = {}) /\ ~(t = {})
        ==> ?x y. x IN s /\ y IN t /\ dist(x,y) = setdist(s,t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN
  MATCH_MP_TAC(MESON[]
   `(!x y. P x /\ Q y ==> S x y) /\ (?x y. P x /\ Q y /\ R x y)
    ==> ?x y. P x /\ Q y /\ R x y /\ S x y`) THEN
  SIMP_TAC[SETDIST_LE_DIST] THEN
  ASM_REWRITE_TAC[REAL_LE_SETDIST_EQ] THEN
  MP_TAC(ISPECL [`{x - y:real^N | x IN s /\ y IN t}`; `vec 0:real^N`]
        DISTANCE_ATTAINS_INF) THEN
  ASM_SIMP_TAC[CLOSED_COMPACT_DIFFERENCES; EXISTS_IN_GSPEC; FORALL_IN_GSPEC;
               DIST_0; GSYM CONJ_ASSOC] THEN
  REWRITE_TAC[dist] THEN DISCH_THEN MATCH_MP_TAC THEN ASM SET_TAC[]);;


let SETDIST_EQ_0_COMPACT_CLOSED = 
prove
 (`!s t:real^N->bool.
        compact s /\ closed t
        ==> (setdist(s,t) = &0 <=> s = {} \/ t = {} \/ ~(s INTER t = {}))`,

  REPEAT STRIP_TAC THEN
  MAP_EVERY ASM_CASES_TAC [`s:real^N->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY] THEN EQ_TAC THENL
   [MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`]
      SETDIST_COMPACT_CLOSED) THEN ASM_REWRITE_TAC[] THEN
    REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY] THEN MESON_TAC[DIST_EQ_0];
    REWRITE_TAC[GSYM REAL_LE_ANTISYM; SETDIST_POS_LE] THEN
    REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY] THEN
    MESON_TAC[SETDIST_LE_DIST; DIST_EQ_0]]);;


let SETDIST_EQ_0_CLOSED_COMPACT = 
prove
 (`!s t:real^N->bool.
        closed s /\ compact t
        ==> (setdist(s,t) = &0 <=> s = {} \/ t = {} \/ ~(s INTER t = {}))`,

  ONCE_REWRITE_TAC[SETDIST_SYM] THEN
  SIMP_TAC[SETDIST_EQ_0_COMPACT_CLOSED] THEN SET_TAC[]);;


let SETDIST_EQ_0_BOUNDED = 
prove
 (`!s t:real^N->bool.
        (bounded s \/ bounded t)
        ==> (setdist(s,t) = &0 <=>
             s = {} \/ t = {} \/ ~(closure(s) INTER closure(t) = {}))`,

  REPEAT GEN_TAC THEN
  MAP_EVERY ASM_CASES_TAC [`s:real^N->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY] THEN STRIP_TAC THEN
  ONCE_REWRITE_TAC[MESON[SETDIST_CLOSURE]
   `setdist(s,t) = setdist(closure s,closure t)`] THEN
  ASM_SIMP_TAC[SETDIST_EQ_0_COMPACT_CLOSED; SETDIST_EQ_0_CLOSED_COMPACT;
               COMPACT_CLOSURE; CLOSED_CLOSURE; CLOSURE_EQ_EMPTY]);;



let SETDIST_TRANSLATION = 
prove
 (`!a:real^N s t.
        setdist(IMAGE (\x. a + x) s,IMAGE (\x. a + x) t) = setdist(s,t)`,

  REPEAT GEN_TAC THEN ONCE_REWRITE_TAC[SETDIST_DIFFERENCES] THEN
  AP_TERM_TAC THEN AP_TERM_TAC THEN
  REWRITE_TAC[SET_RULE
   `{f x y | x IN IMAGE g s /\ y IN IMAGE g t} =
    {f (g x) (g y) | x IN s /\ y IN t}`] THEN
  REWRITE_TAC[VECTOR_ARITH `(a + x) - (a + y):real^N = x - y`]);;

add_translation_invariants [SETDIST_TRANSLATION];;


let SETDIST_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s t.
        linear f /\ (!x. norm(f x) = norm x)
        ==> setdist(IMAGE f s,IMAGE f t) = setdist(s,t)`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[setdist; IMAGE_EQ_EMPTY] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[dist] THEN AP_TERM_TAC THEN
  REWRITE_TAC[SET_RULE
   `{f x y | x IN IMAGE g s /\ y IN IMAGE g t} =
    {f (g x) (g y) | x IN s /\ y IN t}`] THEN
  FIRST_X_ASSUM(fun th -> REWRITE_TAC[GSYM(MATCH_MP LINEAR_SUB th)]) THEN
  ASM_REWRITE_TAC[]);;

add_linear_invariants [SETDIST_LINEAR_IMAGE];;


let SETDIST_UNIQUE = 
prove
 (`!s t a b:real^N d.
        a IN s /\ b IN t /\ dist(a,b) = d /\
        (!x y. x IN s /\ y IN t ==> dist(a,b) <= dist(x,y))
        ==> setdist(s,t) = d`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN CONJ_TAC THENL
   [ASM_MESON_TAC[SETDIST_LE_DIST];
    MATCH_MP_TAC REAL_LE_SETDIST THEN ASM SET_TAC[]]);;


let SETDIST_CLOSEST_POINT = 
prove
 (`!a:real^N s.
      closed s /\ ~(s = {}) ==> setdist({a},s) = dist(a,closest_point s a)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SETDIST_UNIQUE THEN
  REWRITE_TAC[RIGHT_EXISTS_AND_THM; IN_SING; UNWIND_THM2] THEN
  EXISTS_TAC `closest_point s (a:real^N)` THEN
  ASM_MESON_TAC[CLOSEST_POINT_EXISTS; DIST_SYM]);;


let SETDIST_EQ_0_SING = 
prove
 (`(!s x:real^N. setdist({x},s) = &0 <=> s = {} \/ x IN closure s) /\
   (!s x:real^N. setdist(s,{x}) = &0 <=> s = {} \/ x IN closure s)`,

  SIMP_TAC[SETDIST_EQ_0_BOUNDED; BOUNDED_SING; CLOSURE_SING] THEN SET_TAC[]);;


let SETDIST_EQ_0_CLOSED = 
prove
 (`!s x. closed s ==> (setdist({x},s) = &0 <=> s = {} \/ x IN s)`,

  SIMP_TAC[SETDIST_EQ_0_COMPACT_CLOSED; COMPACT_SING] THEN SET_TAC[]);;


let SETDIST_EQ_0_CLOSED_IN = 
prove
 (`!u s x. closed_in (subtopology euclidean u) s /\ x IN u
           ==> (setdist({x},s) = &0 <=> s = {} \/ x IN s)`,

  REWRITE_TAC[SETDIST_EQ_0_SING; CLOSED_IN_INTER_CLOSURE] THEN SET_TAC[]);;


let SETDIST_SING_IN_SET = 
prove
 (`!x s. x IN s ==> setdist({x},s) = &0`,

  SIMP_TAC[SETDIST_EQ_0_SING; REWRITE_RULE[SUBSET] CLOSURE_SUBSET]);;


let SETDIST_SING_TRIANGLE = 
prove
 (`!s x y:real^N. abs(setdist({x},s) - setdist({y},s)) <= dist(x,y)`,

  REPEAT GEN_TAC THEN ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; REAL_SUB_REFL; REAL_ABS_NUM; DIST_POS_LE] THEN
  REWRITE_TAC[GSYM REAL_BOUNDS_LE; REAL_NEG_SUB] THEN REPEAT STRIP_TAC THEN
  ONCE_REWRITE_TAC[REAL_ARITH `a - b <= c <=> a - c <= b`;
                   REAL_ARITH `--a <= b - c <=> c - a <= b`] THEN
  MATCH_MP_TAC REAL_LE_SETDIST THEN ASM_REWRITE_TAC[NOT_INSERT_EMPTY] THEN
  SIMP_TAC[IN_SING; IMP_CONJ; RIGHT_FORALL_IMP_THM; FORALL_UNWIND_THM2] THEN
  X_GEN_TAC `z:real^N` THEN DISCH_TAC THENL
   [MATCH_MP_TAC(NORM_ARITH
     `a <= dist(y:real^N,z) ==> a - dist(x,y) <= dist(x,z)`);
    MATCH_MP_TAC(NORM_ARITH
     `a <= dist(x:real^N,z) ==> a - dist(x,y) <= dist(y,z)`)] THEN
  MATCH_MP_TAC SETDIST_LE_DIST THEN ASM_REWRITE_TAC[IN_SING]);;


let SETDIST_LE_SING = 
prove
 (`!s t x:real^N. x IN s ==> setdist(s,t) <= setdist({x},t)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC SETDIST_SUBSET_LEFT THEN ASM SET_TAC[]);;


let SETDIST_BALLS = 
prove
 (`(!a b:real^N r s.
        setdist(ball(a,r),ball(b,s)) =
        if r <= &0 \/ s <= &0 then &0 else max (&0) (dist(a,b) - (r + s))) /\
   (!a b:real^N r s.
        setdist(ball(a,r),cball(b,s)) =
        if r <= &0 \/ s < &0 then &0 else max (&0) (dist(a,b) - (r + s))) /\
   (!a b:real^N r s.
        setdist(cball(a,r),ball(b,s)) =
        if r < &0 \/ s <= &0 then &0 else max (&0) (dist(a,b) - (r + s))) /\
   (!a b:real^N r s.
        setdist(cball(a,r),cball(b,s)) =
        if r < &0 \/ s < &0 then &0 else max (&0) (dist(a,b) - (r + s)))`,

  REWRITE_TAC[MESON[]
   `(x = if p then y else z) <=> (p ==> x = y) /\ (~p ==> x = z)`] THEN
  SIMP_TAC[TAUT `p \/ q ==> r <=> (p ==> r) /\ (q ==> r)`] THEN
  SIMP_TAC[BALL_EMPTY; CBALL_EMPTY; SETDIST_EMPTY; DE_MORGAN_THM] THEN
  ONCE_REWRITE_TAC[MESON[SETDIST_CLOSURE]
   `setdist(s,t) = setdist(closure s,closure t)`] THEN
  SIMP_TAC[REAL_NOT_LE; REAL_NOT_LT; CLOSURE_BALL] THEN
  REWRITE_TAC[SETDIST_CLOSURE] THEN
  MATCH_MP_TAC(TAUT `(s ==> p /\ q /\ r) /\ s ==> p /\ q /\ r /\ s`) THEN
  CONJ_TAC THENL [MESON_TAC[REAL_LT_IMP_LE]; REPEAT GEN_TAC] THEN
  REWRITE_TAC[real_max; REAL_SUB_LE] THEN COND_CASES_TAC THEN
  SIMP_TAC[SETDIST_EQ_0_BOUNDED; BOUNDED_CBALL; CLOSED_CBALL; CLOSURE_CLOSED;
           CBALL_EQ_EMPTY; INTER_BALLS_EQ_EMPTY]
  THENL [ALL_TAC; ASM_REAL_ARITH_TAC] THEN
  ASM_CASES_TAC `b:real^N = a` THENL
   [FIRST_X_ASSUM SUBST_ALL_TAC THEN
    RULE_ASSUM_TAC(REWRITE_RULE[DIST_REFL]) THEN
    ASM_CASES_TAC `r = &0 /\ s = &0` THENL [ALL_TAC; ASM_REAL_ARITH_TAC] THEN
    ASM_SIMP_TAC[CBALL_SING; SETDIST_SINGS] THEN REAL_ARITH_TAC;
    STRIP_TAC] THEN
  REWRITE_TAC[GSYM REAL_LE_ANTISYM] THEN CONJ_TAC THENL
   [ALL_TAC;
    MATCH_MP_TAC REAL_LE_SETDIST THEN
    ASM_REWRITE_TAC[CBALL_EQ_EMPTY; REAL_NOT_LT; IN_CBALL] THEN
    CONV_TAC NORM_ARITH] THEN
  MATCH_MP_TAC REAL_LE_TRANS THEN
  EXISTS_TAC `dist(a + r / dist(a,b) % (b - a):real^N,
                   b - s / dist(a,b) % (b - a))` THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC SETDIST_LE_DIST THEN
    REWRITE_TAC[IN_CBALL; NORM_ARITH `dist(a:real^N,a + x) = norm x`;
                NORM_ARITH `dist(a:real^N,a - x) = norm x`] THEN
    ONCE_REWRITE_TAC[DIST_SYM] THEN
    REWRITE_TAC[dist; NORM_MUL; REAL_ABS_DIV; REAL_ABS_NORM] THEN
    ASM_SIMP_TAC[REAL_DIV_RMUL; VECTOR_SUB_EQ; NORM_EQ_0] THEN
    ASM_REAL_ARITH_TAC;
    REWRITE_TAC[dist; VECTOR_ARITH
     `(a + d % (b - a)) - (b - e % (b - a)):real^N =
      (&1 - d - e) % (a - b)`] THEN
    REWRITE_TAC[NORM_MUL; REAL_ARITH
      `&1 - r / y - s / y = &1 - (r + s) / y`] THEN
    ONCE_REWRITE_TAC[GSYM REAL_ABS_NORM] THEN
    REWRITE_TAC[GSYM REAL_ABS_MUL] THEN REWRITE_TAC[REAL_ABS_NORM] THEN
    ASM_SIMP_TAC[VECTOR_SUB_EQ; NORM_EQ_0; REAL_FIELD
     `~(n = &0) ==> (&1 - x / n) * n = n - x`] THEN
    REWRITE_TAC[GSYM dist] THEN ASM_REAL_ARITH_TAC]);;

(* ------------------------------------------------------------------------- *)
(* Use set distance for an easy proof of separation properties etc.          *)
(* ------------------------------------------------------------------------- *)


let SEPARATION_CLOSURES = 
prove
 (`!s t:real^N->bool.
        s INTER closure(t) = {} /\ t INTER closure(s) = {}
        ==> ?u v. DISJOINT u v /\ open u /\ open v /\
                  s SUBSET u /\ t SUBSET v`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [MAP_EVERY EXISTS_TAC [`{}:real^N->bool`; `(:real^N)`] THEN
    ASM_REWRITE_TAC[OPEN_EMPTY; OPEN_UNIV] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THENL
   [MAP_EVERY EXISTS_TAC [`(:real^N)`; `{}:real^N->bool`] THEN
    ASM_REWRITE_TAC[OPEN_EMPTY; OPEN_UNIV] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  EXISTS_TAC `{x | x IN (:real^N) /\
                   lift(setdist({x},t) - setdist({x},s)) IN
                   {x | &0 < x$1}}` THEN
  EXISTS_TAC `{x | x IN (:real^N) /\
                   lift(setdist({x},t) - setdist({x},s)) IN
                   {x | x$1 < &0}}` THEN
  REPEAT CONJ_TAC THENL
   [REWRITE_TAC[SET_RULE `DISJOINT s t <=> !x. x IN s /\ x IN t ==> F`] THEN
    REWRITE_TAC[IN_ELIM_THM; IN_UNIV] THEN REAL_ARITH_TAC;
    MATCH_MP_TAC CONTINUOUS_OPEN_PREIMAGE THEN
    SIMP_TAC[REWRITE_RULE[real_gt] OPEN_HALFSPACE_COMPONENT_GT; OPEN_UNIV] THEN
    SIMP_TAC[LIFT_SUB; CONTINUOUS_ON_SUB; CONTINUOUS_ON_LIFT_SETDIST];
    MATCH_MP_TAC CONTINUOUS_OPEN_PREIMAGE THEN
    SIMP_TAC[OPEN_HALFSPACE_COMPONENT_LT; OPEN_UNIV] THEN
    SIMP_TAC[LIFT_SUB; CONTINUOUS_ON_SUB; CONTINUOUS_ON_LIFT_SETDIST];
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_UNIV; GSYM drop; LIFT_DROP] THEN
    GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC(REAL_ARITH
     `&0 <= x /\ y = &0 /\ ~(x = &0) ==> &0 < x - y`);
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_UNIV; GSYM drop; LIFT_DROP] THEN
    GEN_TAC THEN DISCH_TAC THEN MATCH_MP_TAC(REAL_ARITH
     `&0 <= y /\ x = &0 /\ ~(y = &0) ==> x - y < &0`)] THEN
  ASM_SIMP_TAC[SETDIST_POS_LE; SETDIST_EQ_0_BOUNDED; BOUNDED_SING] THEN
  ASM_SIMP_TAC[CLOSED_SING; CLOSURE_CLOSED; NOT_INSERT_EMPTY;
               REWRITE_RULE[SUBSET] CLOSURE_SUBSET;
               SET_RULE `{a} INTER s = {} <=> ~(a IN s)`] THEN
  ASM SET_TAC[]);;


let SEPARATION_NORMAL = 
prove
 (`!s t:real^N->bool.
        closed s /\ closed t /\ s INTER t = {}
        ==> ?u v. open u /\ open v /\
                  s SUBSET u /\ t SUBSET v /\ u INTER v = {}`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GSYM DISJOINT] THEN
  ONCE_REWRITE_TAC[TAUT
    `a /\ b /\ c /\ d /\ e <=> e /\ a /\ b /\ c /\ d`] THEN
  MATCH_MP_TAC SEPARATION_CLOSURES THEN
  ASM_SIMP_TAC[CLOSURE_CLOSED] THEN ASM SET_TAC[]);;


let SEPARATION_NORMAL_LOCAL = 
prove
 (`!s t u:real^N->bool.
        closed_in (subtopology euclidean u) s /\
        closed_in (subtopology euclidean u) t /\
        s INTER t = {}
        ==> ?s' t'. open_in (subtopology euclidean u) s' /\
                    open_in (subtopology euclidean u) t' /\
                    s SUBSET s' /\ t SUBSET t' /\ s' INTER t' = {}`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [MAP_EVERY EXISTS_TAC [`{}:real^N->bool`; `u:real^N->bool`] THEN
    ASM_SIMP_TAC[OPEN_IN_REFL; OPEN_IN_EMPTY; INTER_EMPTY; EMPTY_SUBSET] THEN
    ASM_MESON_TAC[CLOSED_IN_IMP_SUBSET];
    ALL_TAC] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THENL
   [MAP_EVERY EXISTS_TAC [`u:real^N->bool`; `{}:real^N->bool`] THEN
    ASM_SIMP_TAC[OPEN_IN_REFL; OPEN_IN_EMPTY; INTER_EMPTY; EMPTY_SUBSET] THEN
    ASM_MESON_TAC[CLOSED_IN_IMP_SUBSET];
    ALL_TAC] THEN
  EXISTS_TAC `{x:real^N | x IN u /\ setdist({x},s) < setdist({x},t)}` THEN
  EXISTS_TAC `{x:real^N | x IN u /\ setdist({x},t) < setdist({x},s)}` THEN
  SIMP_TAC[EXTENSION; SUBSET; IN_ELIM_THM; SETDIST_SING_IN_SET; IN_INTER;
           NOT_IN_EMPTY; SETDIST_POS_LE; CONJ_ASSOC;
           REAL_ARITH `&0 < x <=> &0 <= x /\ ~(x = &0)`] THEN
  CONJ_TAC THENL [ALL_TAC; MESON_TAC[REAL_LT_ANTISYM]] THEN
  ONCE_REWRITE_TAC[GSYM CONJ_ASSOC] THEN CONJ_TAC THENL
   [ALL_TAC;
    ASM_MESON_TAC[SETDIST_EQ_0_CLOSED_IN; CLOSED_IN_IMP_SUBSET; SUBSET;
                  MEMBER_NOT_EMPTY; IN_INTER]] THEN
  ONCE_REWRITE_TAC[GSYM REAL_SUB_LT] THEN
  ONCE_REWRITE_TAC[MESON[LIFT_DROP] `&0 < x <=> &0 < drop(lift x)`] THEN
  REWRITE_TAC[SET_RULE
   `{x | x IN u /\ &0 < drop(f x)} =
    {x | x IN u /\ f x IN {x | &0 < drop x}}`] THEN
  REWRITE_TAC[drop] THEN CONJ_TAC THEN
  MATCH_MP_TAC CONTINUOUS_OPEN_IN_PREIMAGE THEN
  REWRITE_TAC[OPEN_HALFSPACE_COMPONENT_LT; LIFT_SUB;
           REWRITE_RULE[real_gt] OPEN_HALFSPACE_COMPONENT_GT; OPEN_UNIV] THEN
  SIMP_TAC[CONTINUOUS_ON_SUB; CONTINUOUS_ON_LIFT_SETDIST]);;


let SEPARATION_NORMAL_COMPACT = 
prove
 (`!s t:real^N->bool.
        compact s /\ closed t /\ s INTER t = {}
        ==> ?u v. open u /\ compact(closure u) /\ open v /\
                  s SUBSET u /\ t SUBSET v /\ u INTER v = {}`,

  REWRITE_TAC[COMPACT_EQ_BOUNDED_CLOSED; CLOSED_CLOSURE] THEN
  REPEAT STRIP_TAC THEN FIRST_ASSUM
   (MP_TAC o SPEC `vec 0:real^N` o MATCH_MP BOUNDED_SUBSET_BALL) THEN
  DISCH_THEN(X_CHOOSE_THEN `r:real` STRIP_ASSUME_TAC) THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t UNION ((:real^N) DIFF ball(vec 0,r))`]
        SEPARATION_NORMAL) THEN
  ASM_SIMP_TAC[CLOSED_UNION; GSYM OPEN_CLOSED; OPEN_BALL] THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  REPEAT(MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC) THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  CONJ_TAC THENL [MATCH_MP_TAC BOUNDED_CLOSURE; ASM SET_TAC[]] THEN
  MATCH_MP_TAC BOUNDED_SUBSET THEN EXISTS_TAC `ball(vec 0:real^N,r)` THEN
  REWRITE_TAC[BOUNDED_BALL] THEN ASM SET_TAC[]);;


let SEPARATION_HAUSDORFF = 
prove
 (`!x:real^N y.
      ~(x = y)
      ==> ?u v. open u /\ open v /\ x IN u /\ y IN v /\ (u INTER v = {})`,

  REPEAT STRIP_TAC THEN
  MP_TAC(SPECL [`{x:real^N}`; `{y:real^N}`] SEPARATION_NORMAL) THEN
  REWRITE_TAC[SING_SUBSET; CLOSED_SING] THEN
  DISCH_THEN MATCH_MP_TAC THEN ASM SET_TAC[]);;


let SEPARATION_T2 = 
prove
 (`!x:real^N y.
        ~(x = y) <=> ?u v. open u /\ open v /\ x IN u /\ y IN v /\
                           (u INTER v = {})`,

  REPEAT STRIP_TAC THEN EQ_TAC THEN ASM_SIMP_TAC[SEPARATION_HAUSDORFF] THEN
  REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY] THEN MESON_TAC[]);;


let SEPARATION_T1 = 
prove
 (`!x:real^N y.
        ~(x = y) <=> ?u v. open u /\ open v /\ x IN u /\ ~(y IN u) /\
                           ~(x IN v) /\ y IN v`,

  REPEAT STRIP_TAC THEN EQ_TAC THENL
   [ASM_SIMP_TAC[SEPARATION_T2; EXTENSION; NOT_IN_EMPTY; IN_INTER];
    ALL_TAC] THEN MESON_TAC[]);;


let SEPARATION_T0 = 
prove
 (`!x:real^N y. ~(x = y) <=> ?u. open u /\ ~(x IN u <=> y IN u)`,

  MESON_TAC[SEPARATION_T1]);;

(* ------------------------------------------------------------------------- *)
(* Hausdorff distance between sets.                                          *)
(* ------------------------------------------------------------------------- *)


let hausdist = new_definition
 `hausdist(s:real^N->bool,t:real^N->bool) =
        let ds = {setdist({x},t) | x IN s} UNION {setdist({y},s) | y IN t} in
        if ~(ds = {}) /\ (?b. !d. d IN ds ==> d <= b) then sup ds
        else &0`;;


let HAUSDIST_POS_LE = 
prove
 (`!s t:real^N->bool. &0 <= hausdist(s,t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF] THEN
  REWRITE_TAC[FORALL_IN_GSPEC; FORALL_IN_UNION] THEN
  COND_CASES_TAC THEN REWRITE_TAC[REAL_LE_REFL] THEN
  MATCH_MP_TAC REAL_LE_SUP THEN
  ASM_REWRITE_TAC[FORALL_IN_GSPEC; FORALL_IN_UNION; SETDIST_POS_LE] THEN
  ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN
  ASM_REWRITE_TAC[RIGHT_EXISTS_AND_THM] THEN
  MATCH_MP_TAC(SET_RULE
   `~(s = {}) /\ (!x. x IN s ==> P x) ==> ?y. y IN s /\ P y`) THEN
  ASM_REWRITE_TAC[FORALL_IN_GSPEC; FORALL_IN_UNION; SETDIST_POS_LE]);;


let HAUSDIST_REFL = 
prove
 (`!s:real^N->bool. hausdist(s,s) = &0`,

  GEN_TAC THEN REWRITE_TAC[GSYM REAL_LE_ANTISYM; HAUSDIST_POS_LE] THEN
  REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF] THEN
  COND_CASES_TAC THEN REWRITE_TAC[REAL_LE_REFL] THEN
  MATCH_MP_TAC REAL_SUP_LE THEN
  REWRITE_TAC[FORALL_IN_GSPEC; FORALL_IN_UNION] THEN
  ASM_SIMP_TAC[SETDIST_SING_IN_SET; REAL_LE_REFL]);;


let HAUSDIST_SYM = 
prove
 (`!s t:real^N->bool. hausdist(s,t) = hausdist(t,s)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF] THEN
  GEN_REWRITE_TAC (RAND_CONV o ONCE_DEPTH_CONV) [UNION_COMM] THEN
  REWRITE_TAC[]);;


let HAUSDIST_EMPTY = 
prove
 (`(!t:real^N->bool. hausdist ({},t) = &0) /\
   (!s:real^N->bool. hausdist (s,{}) = &0)`,

  REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF; SETDIST_EMPTY] THEN
  REWRITE_TAC[SET_RULE `{f x | x IN {}} = {}`; UNION_EMPTY] THEN
  REWRITE_TAC[SET_RULE `{c |x| x IN s} = {} <=> s = {}`] THEN
  X_GEN_TAC `s:real^N->bool` THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN ASM_REWRITE_TAC[] THEN
  ASM_SIMP_TAC[SET_RULE `~(s = {}) ==> {c |x| x IN s} = {c}`] THEN
  REWRITE_TAC[SUP_SING; COND_ID]);;


let HAUSDIST_SINGS = 
prove
 (`!x y:real^N. hausdist({x},{y}) = dist(x,y)`,

  REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF; SETDIST_SINGS] THEN
  REWRITE_TAC[SET_RULE `{f x | x IN {a}} = {f a}`] THEN
  REWRITE_TAC[DIST_SYM; UNION_IDEMPOT; SUP_SING; NOT_INSERT_EMPTY] THEN
  REWRITE_TAC[IN_SING; FORALL_UNWIND_THM2] THEN
  MESON_TAC[REAL_LE_REFL]);;


let HAUSDIST_EQ = 
prove
 (`!s t:real^M->bool s' t':real^N->bool.
        (!b. (!x. x IN s ==> setdist({x},t) <= b) /\
             (!y. y IN t ==> setdist({y},s) <= b) <=>
             (!x. x IN s' ==> setdist({x},t') <= b) /\
             (!y. y IN t' ==> setdist({y},s') <= b))
        ==> hausdist(s,t) = hausdist(s',t')`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF] THEN
  MATCH_MP_TAC(MESON[]
   `(p <=> p') /\ s = s'
    ==> (if p then s else &0) = (if p' then s' else &0)`) THEN
  CONJ_TAC THENL
   [BINOP_TAC THENL
     [PURE_REWRITE_TAC[SET_RULE `s = {} <=> !x. x IN s ==> F`];
      AP_TERM_TAC THEN ABS_TAC];
    MATCH_MP_TAC SUP_EQ] THEN
  PURE_REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC] THEN
  ASM_REWRITE_TAC[] THEN
  REWRITE_TAC[DE_MORGAN_THM; NOT_FORALL_THM; MEMBER_NOT_EMPTY] THEN
  REWRITE_TAC[GSYM DE_MORGAN_THM] THEN AP_TERM_TAC THEN EQ_TAC THEN
  DISCH_THEN(fun th -> POP_ASSUM MP_TAC THEN ASSUME_TAC th) THEN
  ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  DISCH_THEN(MP_TAC o SPEC `--(&1):real`) THEN
  SIMP_TAC[SETDIST_POS_LE; REAL_ARITH `&0 <= x ==> ~(x <= --(&1))`] THEN
  SET_TAC[]);;


let HAUSDIST_TRANSLATION = 
prove
 (`!a s t:real^N->bool.
        hausdist(IMAGE (\x. a + x) s,IMAGE (\x. a + x) t) = hausdist(s,t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[hausdist] THEN
  REWRITE_TAC[SET_RULE `{f x | x IN IMAGE g s} = {f(g x) | x IN s}`] THEN
  REWRITE_TAC[SET_RULE `{a + x:real^N} = IMAGE (\x. a + x) {x}`] THEN
  REWRITE_TAC[SETDIST_TRANSLATION]);;

add_translation_invariants [HAUSDIST_TRANSLATION];;


let HAUSDIST_LINEAR_IMAGE = 
prove
 (`!f:real^M->real^N s t.
           linear f /\ (!x. norm(f x) = norm x)
           ==> hausdist(IMAGE f s,IMAGE f t) = hausdist(s,t)`,

  REPEAT STRIP_TAC THEN
  REPEAT GEN_TAC THEN REWRITE_TAC[hausdist] THEN
  REWRITE_TAC[SET_RULE `{f x | x IN IMAGE g s} = {f(g x) | x IN s}`] THEN
  ONCE_REWRITE_TAC[SET_RULE `{(f:real^M->real^N) x} = IMAGE f {x}`] THEN
  ASM_SIMP_TAC[SETDIST_LINEAR_IMAGE]);;

add_linear_invariants [HAUSDIST_LINEAR_IMAGE];;


let HAUSDIST_CLOSURE = 
prove
 (`(!s t:real^N->bool. hausdist(closure s,t) = hausdist(s,t)) /\
   (!s t:real^N->bool. hausdist(s,closure t) = hausdist(s,t))`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC HAUSDIST_EQ THEN
  GEN_TAC THEN BINOP_TAC THEN REWRITE_TAC[SETDIST_CLOSURE] THEN
  PURE_ONCE_REWRITE_TAC[SET_RULE
   `(!x. P x ==> Q x) <=> (!x. P x ==> x IN {x | Q x})`] THEN
  MATCH_MP_TAC FORALL_IN_CLOSURE_EQ THEN
  REWRITE_TAC[EMPTY_GSPEC; CONTINUOUS_ON_ID; CLOSED_EMPTY] THEN
  ONCE_REWRITE_TAC[MESON[LIFT_DROP] `x <= b <=> drop(lift x) <= b`] THEN
  REWRITE_TAC[SET_RULE
    `{x | drop(lift(f x)) <= b} =
     {x | x IN UNIV /\ lift(f x) IN {x | drop x <= b}}`] THEN
  MATCH_MP_TAC CONTINUOUS_CLOSED_PREIMAGE THEN
  REWRITE_TAC[CLOSED_UNIV; CONTINUOUS_ON_LIFT_SETDIST] THEN
  REWRITE_TAC[drop; CLOSED_HALFSPACE_COMPONENT_LE]);;


let REAL_HAUSDIST_LE = 
prove
 (`!s t:real^N->bool b.
        ~(s = {}) /\ ~(t = {}) /\
        (!x. x IN s ==> setdist({x},t) <= b) /\
        (!y. y IN t ==> setdist({y},s) <= b)
        ==> hausdist(s,t) <= b`,

  REPEAT STRIP_TAC THEN
  REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF; SETDIST_SINGS] THEN
  ASM_REWRITE_TAC[EMPTY_UNION; SET_RULE `{f x | x IN s} = {} <=> s = {}`] THEN
  REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC] THEN
  COND_CASES_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
  MATCH_MP_TAC REAL_SUP_LE THEN
  ASM_REWRITE_TAC[EMPTY_UNION; SET_RULE `{f x | x IN s} = {} <=> s = {}`] THEN
  ASM_REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC]);;


let REAL_HAUSDIST_LE_SUMS = 
prove
 (`!s t:real^N->bool b.
        ~(s = {}) /\ ~(t = {}) /\
        s SUBSET {y + z | y IN t /\ z IN cball(vec 0,b)} /\
        t SUBSET {y + z | y IN s /\ z IN cball(vec 0,b)}
        ==> hausdist(s,t) <= b`,

  REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_CBALL_0] THEN
  REWRITE_TAC[VECTOR_ARITH `a:real^N = b + x <=> a - b = x`;
              ONCE_REWRITE_RULE[CONJ_SYM] UNWIND_THM1] THEN
  REWRITE_TAC[GSYM dist] THEN REPEAT STRIP_TAC THEN
  MATCH_MP_TAC REAL_HAUSDIST_LE THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; REAL_LE_TRANS; IN_SING]);;


let REAL_LE_HAUSDIST  = 
prove
 (`!s t:real^N->bool a b c z.
        ~(s = {}) /\ ~(t = {}) /\
        (!x. x IN s ==> setdist({x},t) <= b) /\
        (!y. y IN t ==> setdist({y},s) <= c) /\
        (z IN s /\ a <= setdist({z},t) \/ z IN t /\ a <= setdist({z},s))
        ==> a <= hausdist(s,t)`,

  REPEAT GEN_TAC THEN DISCH_THEN(REPEAT_TCL CONJUNCTS_THEN ASSUME_TAC) THEN
  REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF; SETDIST_SINGS] THEN
  ASM_REWRITE_TAC[EMPTY_UNION; SET_RULE `{f x | x IN s} = {} <=> s = {}`] THEN
  REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC] THEN COND_CASES_TAC THENL
   [MATCH_MP_TAC REAL_LE_SUP THEN
    ASM_SIMP_TAC[EMPTY_UNION; SET_RULE `{f x | x IN s} = {} <=> s = {}`] THEN
    REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC];
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [NOT_EXISTS_THM]) THEN
    ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
    REWRITE_TAC[NOT_FORALL_THM]] THEN
  EXISTS_TAC `max b c:real` THEN
  ASM_SIMP_TAC[REAL_LE_MAX] THEN ASM SET_TAC[]);;


let SETDIST_LE_HAUSDIST = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t ==> setdist(s,t) <= hausdist(s,t)`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; HAUSDIST_EMPTY; REAL_LE_REFL] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; HAUSDIST_EMPTY; REAL_LE_REFL] THEN
  MATCH_MP_TAC REAL_LE_HAUSDIST THEN REWRITE_TAC[CONJ_ASSOC] THEN
  ASM_REWRITE_TAC[RIGHT_EXISTS_AND_THM; LEFT_EXISTS_AND_THM] THEN
  CONJ_TAC THENL
   [ALL_TAC; ASM_MESON_TAC[SETDIST_LE_SING; MEMBER_NOT_EMPTY]] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_REWRITE_TAC[] THEN REWRITE_TAC[bounded; FORALL_IN_GSPEC; GSYM dist] THEN
  DISCH_THEN(X_CHOOSE_TAC `b:real`) THEN
  CONJ_TAC THEN EXISTS_TAC `b:real` THEN REPEAT STRIP_TAC THEN
  ASM_MESON_TAC[REAL_LE_TRANS; SETDIST_LE_DIST; MEMBER_NOT_EMPTY; IN_SING;
                DIST_SYM]);;


let SETDIST_SING_LE_HAUSDIST = 
prove
 (`!s t x:real^N.
        bounded s /\ bounded t /\ x IN s ==> setdist({x},t) <= hausdist(s,t)`,

  REPEAT GEN_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY] THEN
  ASM_CASES_TAC `t:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[SETDIST_EMPTY; HAUSDIST_EMPTY; REAL_LE_REFL] THEN
  STRIP_TAC THEN MATCH_MP_TAC REAL_LE_HAUSDIST THEN
  ASM_REWRITE_TAC[RIGHT_EXISTS_AND_THM] THEN
  REWRITE_TAC[LEFT_EXISTS_AND_THM; EXISTS_OR_THM; CONJ_ASSOC] THEN
  CONJ_TAC THENL [ALL_TAC; ASM_MESON_TAC[REAL_LE_REFL]] THEN CONJ_TAC THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_REWRITE_TAC[] THEN REWRITE_TAC[bounded; FORALL_IN_GSPEC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[GSYM dist] THEN GEN_TAC THENL
   [ALL_TAC; ONCE_REWRITE_TAC[SWAP_FORALL_THM]] THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `y:real^N` THEN
  REPEAT STRIP_TAC THENL
   [UNDISCH_TAC `~(t:real^N->bool = {})`;
    UNDISCH_TAC `~(s:real^N->bool = {})`] THEN
  REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN
  DISCH_THEN(X_CHOOSE_THEN `z:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `z:real^N`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] REAL_LE_TRANS) THENL
   [ALL_TAC; ONCE_REWRITE_TAC[DIST_SYM]] THEN
  MATCH_MP_TAC SETDIST_LE_DIST THEN ASM_REWRITE_TAC[IN_SING]);;


let UPPER_LOWER_HEMICONTINUOUS = 
prove
 (`!f:real^M->real^N->bool t s.
      (!x. x IN s ==> f(x) SUBSET t) /\
      (!u. open_in (subtopology euclidean t) u
           ==> open_in (subtopology euclidean s)
                       {x | x IN s /\ f(x) SUBSET u}) /\
      (!u. closed_in (subtopology euclidean t) u
           ==> closed_in (subtopology euclidean s)
                         {x | x IN s /\ f(x) SUBSET u})
      ==> !x e. x IN s /\ &0 < e /\ bounded(f x)
                ==> ?d. &0 < d /\
                        !x'. x' IN s /\ dist(x,x') < d
                             ==> hausdist(f x,f x') < e`,

  REPEAT GEN_TAC THEN DISCH_TAC THEN REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `(f:real^M->real^N->bool) x = {}` THENL
   [ASM_REWRITE_TAC[HAUSDIST_EMPTY] THEN MESON_TAC[REAL_LT_01]; ALL_TAC] THEN
  FIRST_ASSUM(MP_TAC o SPECL [`x:real^M`; `e / &2`] o MATCH_MP
        UPPER_LOWER_HEMICONTINUOUS_EXPLICIT) THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN
  DISCH_THEN(X_CHOOSE_THEN `d1:real` STRIP_ASSUME_TAC) THEN
  FIRST_ASSUM(MP_TAC o SPEC `vec 0:real^N` o MATCH_MP BOUNDED_SUBSET_BALL) THEN
  DISCH_THEN(X_CHOOSE_THEN `r:real` STRIP_ASSUME_TAC) THEN
  FIRST_ASSUM(MP_TAC o SPEC `t INTER ball(vec 0:real^N,r)` o
        CONJUNCT1 o CONJUNCT2) THEN
  SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_BALL] THEN REWRITE_TAC[open_in] THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^M` o CONJUNCT2) THEN
  ASM_SIMP_TAC[SUBSET_INTER; IN_ELIM_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `d2:real` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `min d1 d2:real` THEN ASM_REWRITE_TAC[REAL_LT_MIN] THEN
  X_GEN_TAC `x':real^M` THEN STRIP_TAC THEN
  REPEAT(FIRST_X_ASSUM(MP_TAC o SPEC `x':real^M`)) THEN
  ASM_REWRITE_TAC[] THEN ONCE_REWRITE_TAC[DIST_SYM] THEN ASM_REWRITE_TAC[] THEN
  STRIP_TAC THEN STRIP_TAC THEN
  ASM_CASES_TAC `(f:real^M->real^N->bool) x' = {}` THEN
  ASM_REWRITE_TAC[HAUSDIST_EMPTY] THEN
  MATCH_MP_TAC(REAL_ARITH `&0 < e /\ x <= e / &2 ==> x < e`) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC REAL_HAUSDIST_LE THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; DIST_SYM; REAL_LE_TRANS;
                IN_SING; REAL_LT_IMP_LE]);;


let HAUSDIST_NONTRIVIAL = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t /\ ~(s = {}) /\ ~(t = {})
        ==> hausdist(s,t) =
            sup({setdist ({x},t) | x IN s} UNION {setdist ({y},s) | y IN t})`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[hausdist; LET_DEF; LET_END_DEF] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [DE_MORGAN_THM]) THEN
  ASM_SIMP_TAC[EMPTY_UNION; SIMPLE_IMAGE; IMAGE_EQ_EMPTY] THEN
  MATCH_MP_TAC(TAUT `p ==> ~p ==> q`) THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_REWRITE_TAC[bounded; FORALL_IN_UNION; FORALL_IN_IMAGE; GSYM dist] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[FORALL_IN_GSPEC] THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; dist; DIST_SYM; REAL_LE_TRANS;
                MEMBER_NOT_EMPTY; IN_SING]);;


let HAUSDIST_NONTRIVIAL_ALT = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t /\ ~(s = {}) /\ ~(t = {})
        ==> hausdist(s,t) = max (sup {setdist ({x},t) | x IN s})
                                (sup {setdist ({y},s) | y IN t})`,

  REPEAT STRIP_TAC THEN ASM_SIMP_TAC[HAUSDIST_NONTRIVIAL] THEN
  MATCH_MP_TAC SUP_UNION THEN
  ASM_REWRITE_TAC[SIMPLE_IMAGE; FORALL_IN_IMAGE; IMAGE_EQ_EMPTY] THEN
  CONJ_TAC THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_REWRITE_TAC[bounded; FORALL_IN_UNION; FORALL_IN_IMAGE; GSYM dist] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[FORALL_IN_GSPEC; GSYM dist] THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; dist; DIST_SYM; REAL_LE_TRANS;
                MEMBER_NOT_EMPTY; IN_SING]);;


let REAL_HAUSDIST_LE_EQ = 
prove
 (`!s t:real^N->bool b.
        ~(s = {}) /\ ~(t = {}) /\ bounded s /\ bounded t
        ==> (hausdist(s,t) <= b <=>
             (!x. x IN s ==> setdist({x},t) <= b) /\
             (!y. y IN t ==> setdist({y},s) <= b))`,

  REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[HAUSDIST_NONTRIVIAL_ALT; REAL_MAX_LE] THEN
  BINOP_TAC THEN
  ONCE_REWRITE_TAC[SET_RULE `(!x. x IN s ==> f x <= b) <=>
                             (!y. y IN {f x | x IN s} ==> y <= b)`] THEN
  MATCH_MP_TAC REAL_SUP_LE_EQ THEN
  ASM_REWRITE_TAC[SIMPLE_IMAGE; IMAGE_EQ_EMPTY; FORALL_IN_IMAGE] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_REWRITE_TAC[bounded; FORALL_IN_UNION; FORALL_IN_IMAGE; GSYM dist] THEN
  MATCH_MP_TAC MONO_EXISTS THEN REWRITE_TAC[FORALL_IN_GSPEC; GSYM dist] THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; dist; DIST_SYM; REAL_LE_TRANS;
                MEMBER_NOT_EMPTY; IN_SING]);;


let HAUSDIST_COMPACT_EXISTS = 
prove
 (`!s t:real^N->bool.
        bounded s /\ compact t /\ ~(t = {})
        ==> !x. x IN s ==> ?y. y IN t /\ dist(x,y) <= hausdist(s,t)`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPECL [`{x:real^N}`; `t:real^N->bool`]
        SETDIST_COMPACT_CLOSED) THEN
  ASM_SIMP_TAC[COMPACT_SING; COMPACT_IMP_CLOSED; NOT_INSERT_EMPTY] THEN
  REWRITE_TAC[IN_SING; UNWIND_THM2; RIGHT_EXISTS_AND_THM; UNWIND_THM1] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `y:real^N` THEN
  REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC REAL_LE_HAUSDIST THEN
  ASM_REWRITE_TAC[LEFT_EXISTS_AND_THM; RIGHT_EXISTS_AND_THM] THEN
  REWRITE_TAC[CONJ_ASSOC] THEN
  CONJ_TAC THENL [CONJ_TAC; ASM_MESON_TAC[REAL_LE_REFL]] THEN
  MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`] BOUNDED_DIFFS) THEN
  ASM_SIMP_TAC[COMPACT_IMP_BOUNDED] THEN
  REWRITE_TAC[bounded; FORALL_IN_GSPEC; GSYM dist] THEN
  MATCH_MP_TAC MONO_EXISTS THEN
  ASM_MESON_TAC[SETDIST_LE_DIST; dist; DIST_SYM; REAL_LE_TRANS;
                MEMBER_NOT_EMPTY; IN_SING]);;


let HAUSDIST_COMPACT_SUMS = 
prove
 (`!s t:real^N->bool.
        bounded s /\ compact t /\ ~(t = {})
        ==> s SUBSET {y + z | y IN t /\ z IN cball(vec 0,hausdist(s,t))}`,

  REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_CBALL_0] THEN
  REWRITE_TAC[VECTOR_ARITH `a:real^N = b + x <=> a - b = x`;
              ONCE_REWRITE_RULE[CONJ_SYM] UNWIND_THM1] THEN
  REWRITE_TAC[GSYM dist; HAUSDIST_COMPACT_EXISTS]);;


let HAUSDIST_TRANS = 
prove
 (`!s t u:real^N->bool.
        bounded s /\ bounded t /\ bounded u /\ ~(t = {})
        ==> hausdist(s,u) <= hausdist(s,t) + hausdist(t,u)`,

  
let lemma = prove
   (`!s t u:real^N->bool.
          bounded s /\ bounded t /\ bounded u /\
          ~(s = {}) /\ ~(t = {}) /\ ~(u = {})
          ==> !x. x IN s ==> setdist({x},u) <= hausdist(s,t) + hausdist(t,u)`,
    REPEAT STRIP_TAC THEN
    MP_TAC(ISPECL [`closure s:real^N->bool`; `closure t:real^N->bool`]
        HAUSDIST_COMPACT_EXISTS) THEN
    ASM_SIMP_TAC[COMPACT_CLOSURE; BOUNDED_CLOSURE; CLOSURE_EQ_EMPTY] THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
    ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET; HAUSDIST_CLOSURE] THEN
    DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC) THEN
    MP_TAC(ISPECL [`closure t:real^N->bool`; `closure u:real^N->bool`]
      HAUSDIST_COMPACT_EXISTS) THEN
    ASM_SIMP_TAC[COMPACT_CLOSURE; BOUNDED_CLOSURE; CLOSURE_EQ_EMPTY] THEN
    DISCH_THEN(MP_TAC o SPEC `y:real^N`) THEN
    ASM_SIMP_TAC[REWRITE_RULE[SUBSET] CLOSURE_SUBSET; HAUSDIST_CLOSURE] THEN
    DISCH_THEN(X_CHOOSE_THEN `z:real^N` STRIP_ASSUME_TAC) THEN
    TRANS_TAC REAL_LE_TRANS `dist(x:real^N,z)` THEN  CONJ_TAC THENL
     [ASM_MESON_TAC[SETDIST_CLOSURE; SETDIST_LE_DIST; IN_SING]; ALL_TAC] THEN
    TRANS_TAC REAL_LE_TRANS `dist(x:real^N,y) + dist(y,z)` THEN
    REWRITE_TAC[DIST_TRIANGLE] THEN ASM_REAL_ARITH_TAC) in
  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[HAUSDIST_EMPTY; REAL_ADD_LID; HAUSDIST_POS_LE] THEN
  ASM_CASES_TAC `u:real^N->bool = {}` THEN
  ASM_REWRITE_TAC[HAUSDIST_EMPTY; REAL_ADD_RID; HAUSDIST_POS_LE] THEN
  ASM_SIMP_TAC[REAL_HAUSDIST_LE_EQ] THEN
  ASM_MESON_TAC[lemma; HAUSDIST_SYM; SETDIST_SYM; REAL_ADD_SYM]);;


let HAUSDIST_EQ_0 = 
prove
 (`!s t:real^N->bool.
      bounded s /\ bounded t
      ==> (hausdist(s,t) = &0 <=> s = {} \/ t = {} \/ closure s = closure t)`,

  REPEAT STRIP_TAC THEN
  MAP_EVERY ASM_CASES_TAC [`s:real^N->bool = {}`; `t:real^N->bool = {}`] THEN
  ASM_REWRITE_TAC[HAUSDIST_EMPTY] THEN
  ASM_SIMP_TAC[GSYM REAL_LE_ANTISYM; HAUSDIST_POS_LE; REAL_HAUSDIST_LE_EQ] THEN
  SIMP_TAC[SETDIST_POS_LE; REAL_ARITH `&0 <= x ==> (x <= &0 <=> x = &0)`] THEN
  ASM_REWRITE_TAC[SETDIST_EQ_0_SING; GSYM SUBSET_ANTISYM_EQ; SUBSET] THEN
  SIMP_TAC[FORALL_IN_CLOSURE_EQ; CLOSED_CLOSURE; CONTINUOUS_ON_ID]);;


let HAUSDIST_COMPACT_NONTRIVIAL = 
prove
 (`!s t:real^N->bool.
        compact s /\ compact t /\ ~(s = {}) /\ ~(t = {})
        ==> hausdist(s,t) =
            inf {e | &0 <= e /\
                   s SUBSET {x + y | x IN t /\ norm y <= e} /\
                   t SUBSET {x + y | x IN s /\ norm y <= e}}`,

  REPEAT STRIP_TAC THEN CONV_TAC SYM_CONV THEN
  MATCH_MP_TAC REAL_INF_UNIQUE THEN
  REWRITE_TAC[FORALL_IN_GSPEC; EXISTS_IN_GSPEC] THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN
  REWRITE_TAC[VECTOR_ARITH `a:real^N = b + x <=> a - b = x`;
              ONCE_REWRITE_RULE[CONJ_SYM] UNWIND_THM1] THEN
  REWRITE_TAC[GSYM dist] THEN CONJ_TAC THENL
   [REPEAT STRIP_TAC THEN
    MATCH_MP_TAC REAL_HAUSDIST_LE THEN
    ASM_MESON_TAC[SETDIST_LE_DIST; DIST_SYM; REAL_LE_TRANS;
                  IN_SING; REAL_LT_IMP_LE];
    REPEAT STRIP_TAC THEN EXISTS_TAC `hausdist(s:real^N->bool,t)` THEN
    ASM_REWRITE_TAC[HAUSDIST_POS_LE] THEN
    ASM_MESON_TAC[DIST_SYM; HAUSDIST_SYM;
                  HAUSDIST_COMPACT_EXISTS; COMPACT_IMP_BOUNDED]]);;


let HAUSDIST_BALLS = 
prove
 (`(!a b:real^N r s.
        hausdist(ball(a,r),ball(b,s)) =
        if r <= &0 \/ s <= &0 then &0 else dist(a,b) + abs(r - s)) /\
   (!a b:real^N r s.
        hausdist(ball(a,r),cball(b,s)) =
        if r <= &0 \/ s < &0 then &0 else dist(a,b) + abs(r - s)) /\
   (!a b:real^N r s.
        hausdist(cball(a,r),ball(b,s)) =
        if r < &0 \/ s <= &0 then &0 else dist(a,b) + abs(r - s)) /\
   (!a b:real^N r s.
        hausdist(cball(a,r),cball(b,s)) =
        if r < &0 \/ s < &0 then &0 else dist(a,b) + abs(r - s))`,

  REWRITE_TAC[MESON[]
   `(x = if p then y else z) <=> (p ==> x = y) /\ (~p ==> x = z)`] THEN
  SIMP_TAC[TAUT `p \/ q ==> r <=> (p ==> r) /\ (q ==> r)`] THEN
  SIMP_TAC[BALL_EMPTY; CBALL_EMPTY; HAUSDIST_EMPTY; DE_MORGAN_THM] THEN
  ONCE_REWRITE_TAC[MESON[HAUSDIST_CLOSURE]
   `hausdist(s,t) = hausdist(closure s,closure t)`] THEN
  SIMP_TAC[REAL_NOT_LE; REAL_NOT_LT; CLOSURE_BALL] THEN
  REWRITE_TAC[HAUSDIST_CLOSURE] THEN
  MATCH_MP_TAC(TAUT `(s ==> p /\ q /\ r) /\ s ==> p /\ q /\ r /\ s`) THEN
  CONJ_TAC THENL [MESON_TAC[REAL_LT_IMP_LE]; REPEAT STRIP_TAC] THEN
  ASM_SIMP_TAC[HAUSDIST_NONTRIVIAL; BOUNDED_CBALL; CBALL_EQ_EMPTY;
               REAL_NOT_LT] THEN
  MATCH_MP_TAC SUP_UNIQUE THEN
  REWRITE_TAC[FORALL_IN_GSPEC; FORALL_IN_UNION] THEN
  REWRITE_TAC[MESON[CBALL_SING] `{a} = cball(a:real^N,&0)`] THEN
  ASM_REWRITE_TAC[SETDIST_BALLS; REAL_LT_REFL] THEN
  X_GEN_TAC `c:real` THEN REWRITE_TAC[IN_CBALL] THEN
  EQ_TAC THENL [ALL_TAC; NORM_ARITH_TAC] THEN
  ASM_CASES_TAC `b:real^N = a` THENL
   [ASM_REWRITE_TAC[DIST_SYM; DIST_REFL; REAL_MAX_LE] THEN
    DISCH_THEN(CONJUNCTS_THEN2
     (MP_TAC o SPEC `a + r % basis 1:real^N`)
     (MP_TAC o SPEC `a + s % basis 1:real^N`)) THEN
    REWRITE_TAC[NORM_ARITH `dist(a:real^N,a + x) = norm x`] THEN
    SIMP_TAC[NORM_MUL; NORM_BASIS; LE_REFL; DIMINDEX_GE_1] THEN
    ASM_REAL_ARITH_TAC;
    DISCH_THEN(CONJUNCTS_THEN2
     (MP_TAC o SPEC `a - r / dist(a,b) % (b - a):real^N`)
     (MP_TAC o SPEC `b - s / dist(a,b) % (a - b):real^N`)) THEN
    REWRITE_TAC[NORM_ARITH `dist(a:real^N,a - x) = norm x`] THEN
    REWRITE_TAC[dist; NORM_MUL; VECTOR_ARITH
     `b - e % (a - b) - a:real^N = (&1 + e) % (b - a)`] THEN
    ONCE_REWRITE_TAC[GSYM REAL_ABS_NORM] THEN
    REWRITE_TAC[GSYM REAL_ABS_MUL] THEN REWRITE_TAC[REAL_ABS_NORM] THEN
    REWRITE_TAC[NORM_SUB; REAL_ADD_RDISTRIB; REAL_MUL_LID] THEN
    ASM_SIMP_TAC[REAL_DIV_RMUL; NORM_EQ_0; VECTOR_SUB_EQ] THEN
    ASM_REAL_ARITH_TAC]);;


let HAUSDIST_ALT = 
prove
 (`!s t:real^N->bool.
        bounded s /\ bounded t /\ ~(s = {}) /\ ~(t = {})
        ==> hausdist(s,t) =
            sup {abs(setdist({x},s) - setdist({x},t)) | x IN (:real^N)}`,

  REPEAT GEN_TAC THEN
  ONCE_REWRITE_TAC[GSYM COMPACT_CLOSURE; GSYM(CONJUNCT2 SETDIST_CLOSURE);
    GSYM CLOSURE_EQ_EMPTY; MESON[HAUSDIST_CLOSURE]
    `hausdist(s:real^N->bool,t) = hausdist(closure s,closure t)`] THEN
  SPEC_TAC(`closure t:real^N->bool`,`t:real^N->bool`) THEN
  SPEC_TAC(`closure s:real^N->bool`,`s:real^N->bool`) THEN
  REPEAT STRIP_TAC THEN
  ASM_SIMP_TAC[HAUSDIST_NONTRIVIAL; COMPACT_IMP_BOUNDED] THEN
  MATCH_MP_TAC SUP_EQ THEN
  REWRITE_TAC[FORALL_IN_UNION; FORALL_IN_GSPEC; IN_UNIV] THEN
  REWRITE_TAC[REAL_ARITH `abs(y - x) <= b <=> x <= y + b /\ y <= x + b`] THEN
  GEN_TAC THEN REWRITE_TAC[FORALL_AND_THM] THEN BINOP_TAC THEN
  (EQ_TAC THENL [ALL_TAC; MESON_TAC[SETDIST_SING_IN_SET; REAL_ADD_LID]]) THEN
  DISCH_TAC THEN X_GEN_TAC `z:real^N` THENL
   [MP_TAC(ISPECL[`{z:real^N}`; `s:real^N->bool`] SETDIST_CLOSED_COMPACT);
    MP_TAC(ISPECL[`{z:real^N}`; `t:real^N->bool`] SETDIST_CLOSED_COMPACT)] THEN
  ASM_REWRITE_TAC[CLOSED_SING; NOT_INSERT_EMPTY] THEN
  REWRITE_TAC[IN_SING; RIGHT_EXISTS_AND_THM; UNWIND_THM2] THEN
  DISCH_THEN(X_CHOOSE_THEN `y:real^N` (STRIP_ASSUME_TAC o GSYM)) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN ASM_REWRITE_TAC[] THENL
   [MP_TAC(ISPECL[`{y:real^N}`; `t:real^N->bool`] SETDIST_CLOSED_COMPACT);
    MP_TAC(ISPECL[`{y:real^N}`; `s:real^N->bool`] SETDIST_CLOSED_COMPACT)] THEN
  ASM_REWRITE_TAC[CLOSED_SING; NOT_INSERT_EMPTY] THEN
  REWRITE_TAC[IN_SING; RIGHT_EXISTS_AND_THM; UNWIND_THM2] THEN
  DISCH_THEN(X_CHOOSE_THEN `x:real^N` (STRIP_ASSUME_TAC o GSYM)) THEN
  ASM_REWRITE_TAC[] THEN DISCH_TAC THEN
  TRANS_TAC REAL_LE_TRANS `dist(z:real^N,x)` THEN
  ASM_SIMP_TAC[SETDIST_LE_DIST; IN_SING] THEN
  UNDISCH_TAC `dist(y:real^N,x) <= b` THEN CONV_TAC NORM_ARITH);;


let CONTINUOUS_DIAMETER = 
prove
 (`!s:real^N->bool e.
        bounded s /\ ~(s = {}) /\ &0 < e
        ==> ?d. &0 < d /\
                !t. bounded t /\ ~(t = {}) /\ hausdist(s,t) < d
                    ==> abs(diameter s - diameter t) < e`,

  REPEAT STRIP_TAC THEN EXISTS_TAC `e / &2` THEN
  ASM_REWRITE_TAC[REAL_HALF] THEN REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `diameter(s:real^N->bool) - diameter(t:real^N->bool) =
                diameter(closure s) - diameter(closure t)`
  SUBST1_TAC THENL [ASM_MESON_TAC[DIAMETER_CLOSURE]; ALL_TAC] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `&2 * hausdist(s:real^N->bool,t)` THEN
  CONJ_TAC THENL [ALL_TAC; ASM_REAL_ARITH_TAC] THEN
  MP_TAC(ISPECL [`vec 0:real^N`; `hausdist(s:real^N->bool,t)`]
    DIAMETER_CBALL) THEN
  ASM_SIMP_TAC[HAUSDIST_POS_LE; GSYM REAL_NOT_LE] THEN
  DISCH_THEN(SUBST1_TAC o SYM) THEN MATCH_MP_TAC(REAL_ARITH
   `x <= y + e /\ y <= x + e ==> abs(x - y) <= e`) THEN
  CONJ_TAC THEN
  W(MP_TAC o PART_MATCH (rand o rand) DIAMETER_SUMS o rand o snd) THEN
  ASM_SIMP_TAC[BOUNDED_CBALL; BOUNDED_CLOSURE] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] REAL_LE_TRANS) THEN
  MATCH_MP_TAC DIAMETER_SUBSET THEN
  ASM_SIMP_TAC[BOUNDED_SUMS; BOUNDED_CBALL; BOUNDED_CLOSURE] THEN
  ONCE_REWRITE_TAC[MESON[HAUSDIST_CLOSURE]
   `hausdist(s:real^N->bool,t) = hausdist(closure s,closure t)`]
  THENL [ALL_TAC; ONCE_REWRITE_TAC[HAUSDIST_SYM]] THEN
  MATCH_MP_TAC HAUSDIST_COMPACT_SUMS THEN
  ASM_SIMP_TAC[COMPACT_CLOSURE; BOUNDED_CLOSURE; CLOSURE_EQ_EMPTY]);;

(* ------------------------------------------------------------------------- *)
(* Isometries are embeddings, and even surjective in the compact case.       *)
(* ------------------------------------------------------------------------- *)


let ISOMETRY_IMP_OPEN_MAP = 
prove
 (`!f:real^M->real^N s t u.
        IMAGE f s = t /\
        (!x y. x IN s /\ y IN s ==> dist(f x,f y) = dist(x,y)) /\
        open_in (subtopology euclidean s) u
        ==> open_in (subtopology euclidean t) (IMAGE f u)`,

  REWRITE_TAC[open_in; FORALL_IN_IMAGE] THEN REPEAT GEN_TAC THEN STRIP_TAC THEN
  CONJ_TAC THENL [ASM SET_TAC[]; X_GEN_TAC `x:real^M` THEN DISCH_TAC] THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `x:real^M`) THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `e:real` THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[IMP_CONJ] THEN
  EXPAND_TAC "t" THEN REWRITE_TAC[FORALL_IN_IMAGE] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[SUBSET]) THEN
  ASM_SIMP_TAC[IN_IMAGE] THEN ASM_MESON_TAC[]);;


let ISOMETRY_IMP_EMBEDDING = 
prove
 (`!f:real^M->real^N s t.
        IMAGE f s = t /\ (!x y. x IN s /\ y IN s ==> dist(f x,f y) = dist(x,y))
        ==> ?g. homeomorphism (s,t) (f,g)`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC HOMEOMORPHISM_INJECTIVE_OPEN_MAP THEN
  ASM_SIMP_TAC[ISOMETRY_ON_IMP_CONTINUOUS_ON] THEN
  CONJ_TAC THENL [ASM_MESON_TAC[DIST_EQ_0]; REPEAT STRIP_TAC] THEN
  MATCH_MP_TAC ISOMETRY_IMP_OPEN_MAP THEN ASM_MESON_TAC[]);;


let ISOMETRY_IMP_HOMEOMORPHISM_COMPACT = 
prove
 (`!f s:real^N->bool.
        compact s /\ IMAGE f s SUBSET s /\
        (!x y. x IN s /\ y IN s ==> dist(f x,f y) = dist(x,y))
        ==> ?g. homeomorphism (s,s) (f,g)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN `IMAGE (f:real^N->real^N) s = s`
   (fun th -> ASM_MESON_TAC[th; ISOMETRY_IMP_EMBEDDING]) THEN
  FIRST_ASSUM(ASSUME_TAC o MATCH_MP ISOMETRY_ON_IMP_CONTINUOUS_ON) THEN
  ASM_REWRITE_TAC[GSYM SUBSET_ANTISYM_EQ] THEN REWRITE_TAC[SUBSET] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  SUBGOAL_THEN `setdist({x},IMAGE (f:real^N->real^N) s) = &0` MP_TAC THENL
   [MATCH_MP_TAC(REAL_ARITH `&0 <= x /\ ~(&0 < x) ==> x = &0`) THEN
    REWRITE_TAC[SETDIST_POS_LE] THEN DISCH_TAC THEN
    (X_CHOOSE_THEN `z:num->real^N` STRIP_ASSUME_TAC o
     prove_recursive_functions_exist num_RECURSION)
     `z 0 = (x:real^N) /\ !n. z(SUC n) = f(z n)` THEN
    SUBGOAL_THEN `!n. (z:num->real^N) n IN s` ASSUME_TAC THENL
     [INDUCT_TAC THEN ASM SET_TAC[]; ALL_TAC] THEN
    FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [compact]) THEN
    DISCH_THEN(MP_TAC o SPEC `z:num->real^N`) THEN
    ASM_REWRITE_TAC[NOT_EXISTS_THM] THEN
    MAP_EVERY X_GEN_TAC [`l:real^N`; `r:num->num`] THEN STRIP_TAC THEN
    FIRST_ASSUM(MP_TAC o MATCH_MP CONVERGENT_IMP_CAUCHY) THEN
    REWRITE_TAC[cauchy] THEN
    DISCH_THEN(MP_TAC o SPEC `setdist({x},IMAGE (f:real^N->real^N) s)`) THEN
    ASM_REWRITE_TAC[] THEN DISCH_THEN(X_CHOOSE_THEN `N:num`
     (MP_TAC o SPECL [`N:num`; `N + 1`])) THEN
    ANTS_TAC THENL [ARITH_TAC; REWRITE_TAC[REAL_NOT_LT; o_THM]] THEN
    SUBGOAL_THEN `(r:num->num) N < r (N + 1)` MP_TAC THENL
     [FIRST_X_ASSUM MATCH_MP_TAC THEN ARITH_TAC;
      REWRITE_TAC[LT_EXISTS; LEFT_IMP_EXISTS_THM]] THEN
    X_GEN_TAC `d:num` THEN DISCH_THEN SUBST1_TAC THEN
    TRANS_TAC REAL_LE_TRANS `dist(x:real^N,z(SUC d))` THEN CONJ_TAC THENL
     [MATCH_MP_TAC SETDIST_LE_DIST THEN ASM SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC REAL_EQ_IMP_LE THEN
    SPEC_TAC(`(r:num->num) N`,`m:num`) THEN
    INDUCT_TAC THEN ASM_MESON_TAC[ADD_CLAUSES];
    REWRITE_TAC[SETDIST_EQ_0_SING; IMAGE_EQ_EMPTY] THEN
    ASM_MESON_TAC[COMPACT_IMP_CLOSED; NOT_IN_EMPTY;
                  COMPACT_CONTINUOUS_IMAGE; CLOSURE_CLOSED]]);;

(* ------------------------------------------------------------------------- *)
(* Urysohn's lemma (for real^N, where the proof is easy using distances).    *)
(* ------------------------------------------------------------------------- *)


let URYSOHN_LOCAL_STRONG = 
prove
 (`!s t u a b.
        closed_in (subtopology euclidean u) s /\
        closed_in (subtopology euclidean u) t /\
        s INTER t = {} /\ ~(a = b)
        ==> ?f:real^N->real^M.
               f continuous_on u /\
               (!x. x IN u ==> f(x) IN segment[a,b]) /\
               (!x. x IN u ==> (f x = a <=> x IN s)) /\
               (!x. x IN u ==> (f x = b <=> x IN t))`,

  
let lemma = prove
   (`!s t u a b.
          closed_in (subtopology euclidean u) s /\
          closed_in (subtopology euclidean u) t /\
          s INTER t = {} /\ ~(s = {}) /\ ~(t = {}) /\ ~(a = b)
          ==> ?f:real^N->real^M.
                 f continuous_on u /\
                 (!x. x IN u ==> f(x) IN segment[a,b]) /\
                 (!x. x IN u ==> (f x = a <=> x IN s)) /\
                 (!x. x IN u ==> (f x = b <=> x IN t))`,
    REPEAT STRIP_TAC THEN EXISTS_TAC
      `\x:real^N. a + setdist({x},s) / (setdist({x},s) + setdist({x},t)) %
                      (b - a:real^M)` THEN REWRITE_TAC[] THEN
    SUBGOAL_THEN
     `(!x:real^N. x IN u ==> (setdist({x},s) = &0 <=> x IN s)) /\
      (!x:real^N. x IN u ==> (setdist({x},t) = &0 <=> x IN t))`
    STRIP_ASSUME_TAC THENL
     [ASM_REWRITE_TAC[SETDIST_EQ_0_SING] THEN CONJ_TAC THENL
       [MP_TAC(ISPEC `s:real^N->bool` CLOSED_IN_CLOSED);
        MP_TAC(ISPEC `t:real^N->bool` CLOSED_IN_CLOSED)] THEN
      DISCH_THEN(MP_TAC o SPEC `u:real^N->bool`) THEN
      ASM_REWRITE_TAC[] THEN DISCH_THEN(X_CHOOSE_THEN `v:real^N->bool`
       (CONJUNCTS_THEN2 ASSUME_TAC SUBST_ALL_TAC)) THEN
      ASM_MESON_TAC[CLOSURE_CLOSED; INTER_SUBSET; SUBSET_CLOSURE; SUBSET;
                    IN_INTER; CLOSURE_SUBSET];
      ALL_TAC] THEN
    SUBGOAL_THEN `!x:real^N. x IN u ==> &0 < setdist({x},s) + setdist({x},t)`
    ASSUME_TAC THENL
     [REPEAT STRIP_TAC THEN MATCH_MP_TAC(REAL_ARITH
        `&0 <= x /\ &0 <= y /\ ~(x = &0 /\ y = &0) ==> &0 < x + y`) THEN
      REWRITE_TAC[SETDIST_POS_LE] THEN ASM SET_TAC[];
      ALL_TAC] THEN
    REPEAT CONJ_TAC THENL
     [MATCH_MP_TAC CONTINUOUS_ON_ADD THEN REWRITE_TAC[CONTINUOUS_ON_CONST] THEN
      REWRITE_TAC[real_div; GSYM VECTOR_MUL_ASSOC] THEN
      REPEAT(MATCH_MP_TAC CONTINUOUS_ON_MUL THEN CONJ_TAC) THEN
      REWRITE_TAC[CONTINUOUS_ON_CONST; o_DEF] THEN
      REWRITE_TAC[CONTINUOUS_ON_LIFT_SETDIST] THEN
      MATCH_MP_TAC(REWRITE_RULE[o_DEF] CONTINUOUS_ON_INV) THEN
      ASM_SIMP_TAC[REAL_LT_IMP_NZ] THEN
      REWRITE_TAC[LIFT_ADD] THEN MATCH_MP_TAC CONTINUOUS_ON_ADD THEN
      REWRITE_TAC[CONTINUOUS_ON_LIFT_SETDIST];
      X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
      REWRITE_TAC[segment; IN_ELIM_THM] THEN
      REWRITE_TAC[VECTOR_MUL_EQ_0; LEFT_OR_DISTRIB; VECTOR_ARITH
       `a + x % (b - a):real^N = (&1 - u) % a + u % b <=>
        (x - u) % (b - a) = vec 0`;
       EXISTS_OR_THM] THEN
      DISJ1_TAC THEN ONCE_REWRITE_TAC[CONJ_SYM] THEN
      REWRITE_TAC[REAL_SUB_0; UNWIND_THM1] THEN
      ASM_SIMP_TAC[REAL_LE_DIV; REAL_LE_ADD; SETDIST_POS_LE; REAL_LE_LDIV_EQ;
                   REAL_ARITH `a <= &1 * (a + b) <=> &0 <= b`];
      REWRITE_TAC[VECTOR_ARITH `a + x:real^N = a <=> x = vec 0`];
      REWRITE_TAC[VECTOR_ARITH `a + x % (b - a):real^N = b <=>
                                (x - &1) % (b - a) = vec 0`]] THEN
    ASM_REWRITE_TAC[VECTOR_MUL_EQ_0; VECTOR_SUB_EQ] THEN
    ASM_SIMP_TAC[REAL_SUB_0; REAL_EQ_LDIV_EQ;
                 REAL_MUL_LZERO; REAL_MUL_LID] THEN
    REWRITE_TAC[REAL_ARITH `x:real = x + y <=> y = &0`] THEN
    ASM_REWRITE_TAC[]) in
  MATCH_MP_TAC(MESON[]
   `(!s t. P s t <=> P t s) /\
    (!s t. ~(s = {}) /\ ~(t = {}) ==> P s t) /\
    P {} {} /\ (!t. ~(t = {}) ==> P {} t)
    ==> !s t. P s t`) THEN
  REPEAT CONJ_TAC THENL
   [REPEAT GEN_TAC THEN
    GEN_REWRITE_TAC (RAND_CONV o BINDER_CONV) [SWAP_FORALL_THM] THEN
    REPEAT(AP_TERM_TAC THEN ABS_TAC) THEN
    REWRITE_TAC[SEGMENT_SYM; INTER_COMM; CONJ_ACI; EQ_SYM_EQ];
    SIMP_TAC[lemma];
    REPEAT STRIP_TAC THEN EXISTS_TAC `(\x. midpoint(a,b)):real^N->real^M` THEN
    ASM_SIMP_TAC[NOT_IN_EMPTY; CONTINUOUS_ON_CONST; MIDPOINT_IN_SEGMENT] THEN
    REWRITE_TAC[midpoint] THEN CONJ_TAC THEN GEN_TAC THEN DISCH_TAC THEN
    UNDISCH_TAC `~(a:real^M = b)` THEN REWRITE_TAC[CONTRAPOS_THM] THEN
    VECTOR_ARITH_TAC;
    REPEAT STRIP_TAC THEN ASM_CASES_TAC `t:real^N->bool = u` THENL
     [EXISTS_TAC `(\x. b):real^N->real^M` THEN
      ASM_REWRITE_TAC[NOT_IN_EMPTY; ENDS_IN_SEGMENT; IN_UNIV;
                      CONTINUOUS_ON_CONST];
      SUBGOAL_THEN `?c:real^N. c IN u /\ ~(c IN t)` STRIP_ASSUME_TAC THENL
       [REPEAT(FIRST_X_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_SUBSET)) THEN
        REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN ASM SET_TAC[];
        ALL_TAC] THEN
      MP_TAC(ISPECL [`{c:real^N}`; `t:real^N->bool`; `u:real^N->bool`;
                     `midpoint(a,b):real^M`; `b:real^M`] lemma) THEN
      ASM_REWRITE_TAC[CLOSED_IN_SING; MIDPOINT_EQ_ENDPOINT] THEN
      ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      MATCH_MP_TAC MONO_EXISTS THEN SIMP_TAC[NOT_IN_EMPTY] THEN
      X_GEN_TAC `f:real^N->real^M` THEN STRIP_TAC THEN CONJ_TAC THENL
       [SUBGOAL_THEN
         `segment[midpoint(a,b):real^M,b] SUBSET segment[a,b]` MP_TAC
        THENL
         [REWRITE_TAC[SUBSET; IN_SEGMENT; midpoint] THEN GEN_TAC THEN
          DISCH_THEN(X_CHOOSE_THEN `u:real` STRIP_ASSUME_TAC) THEN
          EXISTS_TAC `(&1 + u) / &2` THEN ASM_REWRITE_TAC[] THEN
          REPEAT(CONJ_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC]) THEN
          VECTOR_ARITH_TAC;
          ASM SET_TAC[]];
        SUBGOAL_THEN `~(a IN segment[midpoint(a,b):real^M,b])` MP_TAC THENL
         [ALL_TAC; ASM_MESON_TAC[]] THEN
        DISCH_THEN(MP_TAC o CONJUNCT2 o MATCH_MP DIST_IN_CLOSED_SEGMENT) THEN
        REWRITE_TAC[DIST_MIDPOINT] THEN
        UNDISCH_TAC `~(a:real^M = b)` THEN NORM_ARITH_TAC]]]);;


let URYSOHN_LOCAL = 
prove
 (`!s t u a b.
        closed_in (subtopology euclidean u) s /\
        closed_in (subtopology euclidean u) t /\
        s INTER t = {}
        ==> ?f:real^N->real^M.
               f continuous_on u /\
               (!x. x IN u ==> f(x) IN segment[a,b]) /\
               (!x. x IN s ==> f x = a) /\
               (!x. x IN t ==> f x = b)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `a:real^M = b` THENL
   [EXISTS_TAC `(\x. b):real^N->real^M` THEN
    ASM_REWRITE_TAC[ENDS_IN_SEGMENT; CONTINUOUS_ON_CONST];
    MP_TAC(ISPECL [`s:real^N->bool`; `t:real^N->bool`; `u:real^N->bool`;
                   `a:real^M`; `b:real^M`] URYSOHN_LOCAL_STRONG) THEN
    ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN SIMP_TAC[] THEN
    REPEAT(FIRST_X_ASSUM(MP_TAC o MATCH_MP CLOSED_IN_SUBSET)) THEN
    REWRITE_TAC[TOPSPACE_EUCLIDEAN_SUBTOPOLOGY] THEN SET_TAC[]]);;


let URYSOHN_STRONG = 
prove
 (`!s t a b.
        closed s /\ closed t /\ s INTER t = {} /\ ~(a = b)
        ==> ?f:real^N->real^M.
               f continuous_on (:real^N) /\ (!x. f(x) IN segment[a,b]) /\
               (!x. f x = a <=> x IN s) /\ (!x. f x = b <=> x IN t)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN] THEN
  ONCE_REWRITE_TAC[GSYM SUBTOPOLOGY_UNIV] THEN
  DISCH_THEN(MP_TAC o MATCH_MP URYSOHN_LOCAL_STRONG) THEN
  REWRITE_TAC[IN_UNIV]);;


let URYSOHN = 
prove
 (`!s t a b.
        closed s /\ closed t /\ s INTER t = {}
        ==> ?f:real^N->real^M.
               f continuous_on (:real^N) /\ (!x. f(x) IN segment[a,b]) /\
               (!x. x IN s ==> f x = a) /\ (!x. x IN t ==> f x = b)`,

  REPEAT GEN_TAC THEN REWRITE_TAC[CLOSED_IN] THEN
  ONCE_REWRITE_TAC[GSYM SUBTOPOLOGY_UNIV] THEN DISCH_THEN
   (MP_TAC o ISPECL [`a:real^M`; `b:real^M`] o MATCH_MP URYSOHN_LOCAL) THEN
  REWRITE_TAC[IN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Countability of some relevant sets.                                       *)
(* ------------------------------------------------------------------------- *)


let COUNTABLE_INTEGER = 
prove
 (`COUNTABLE integer`,

  MATCH_MP_TAC COUNTABLE_SUBSET THEN EXISTS_TAC
   `IMAGE (\n. (&n:real)) (:num) UNION IMAGE (\n. --(&n)) (:num)` THEN
  SIMP_TAC[COUNTABLE_IMAGE; COUNTABLE_UNION; NUM_COUNTABLE] THEN
  REWRITE_TAC[SUBSET; IN_UNION; IN_IMAGE; IN_UNIV] THEN
  REWRITE_TAC[IN; INTEGER_CASES]);;


let CARD_EQ_INTEGER = 
prove
 (`integer =_c (:num)`,

  REWRITE_TAC[GSYM CARD_LE_ANTISYM; GSYM COUNTABLE_ALT; COUNTABLE_INTEGER] THEN
  REWRITE_TAC[le_c] THEN EXISTS_TAC `real_of_num` THEN
  REWRITE_TAC[IN_UNIV; REAL_OF_NUM_EQ] THEN
  REWRITE_TAC[IN; INTEGER_CLOSED]);;


let COUNTABLE_RATIONAL = 
prove
 (`COUNTABLE rational`,

  MATCH_MP_TAC COUNTABLE_SUBSET THEN
  EXISTS_TAC `IMAGE (\(x,y). x / y) (integer CROSS integer)` THEN
  SIMP_TAC[COUNTABLE_IMAGE; COUNTABLE_CROSS; COUNTABLE_INTEGER] THEN
  REWRITE_TAC[SUBSET; IN_IMAGE; EXISTS_PAIR_THM; IN_CROSS] THEN
  REWRITE_TAC[rational; IN] THEN MESON_TAC[]);;


let CARD_EQ_RATIONAL = 
prove
 (`rational =_c (:num)`,

  REWRITE_TAC[GSYM CARD_LE_ANTISYM; GSYM COUNTABLE_ALT; COUNTABLE_RATIONAL] THEN
  REWRITE_TAC[le_c] THEN EXISTS_TAC `real_of_num` THEN
  REWRITE_TAC[IN_UNIV; REAL_OF_NUM_EQ] THEN
  REWRITE_TAC[IN; RATIONAL_CLOSED]);;


let COUNTABLE_INTEGER_COORDINATES = 
prove
 (`COUNTABLE { x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> integer(x$i) }`,

  MATCH_MP_TAC COUNTABLE_CART THEN
  REWRITE_TAC[SET_RULE `{x | P x} = P`; COUNTABLE_INTEGER]);;


let COUNTABLE_RATIONAL_COORDINATES = 
prove
 (`COUNTABLE { x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i) }`,

  MATCH_MP_TAC COUNTABLE_CART THEN
  REWRITE_TAC[SET_RULE `{x | P x} = P`; COUNTABLE_RATIONAL]);;

(* ------------------------------------------------------------------------- *)
(* Density of points with rational, or just dyadic rational, coordinates.    *)
(* ------------------------------------------------------------------------- *)


let CLOSURE_DYADIC_RATIONALS = 
prove
 (`closure { inv(&2 pow n) % x |n,x|
             !i. 1 <= i /\ i <= dimindex(:N) ==> integer(x$i) } = (:real^N)`,

  REWRITE_TAC[EXTENSION; CLOSURE_APPROACHABLE; IN_UNIV; EXISTS_IN_GSPEC] THEN
  MAP_EVERY X_GEN_TAC [`x:real^N`; `e:real`] THEN DISCH_TAC THEN
  MP_TAC(SPECL [`inv(&2)`; `e / &(dimindex(:N))`] REAL_ARCH_POW_INV) THEN
  ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; LE_1; DIMINDEX_GE_1;
               REAL_POW_INV; REAL_LT_RDIV_EQ] THEN
  CONV_TAC REAL_RAT_REDUCE_CONV THEN MATCH_MP_TAC MONO_EXISTS THEN
  ONCE_REWRITE_TAC[REAL_MUL_SYM] THEN X_GEN_TAC `n:num` THEN DISCH_TAC THEN
  EXISTS_TAC `(lambda i. floor(&2 pow n * (x:real^N)$i)):real^N` THEN
  ASM_SIMP_TAC[LAMBDA_BETA; FLOOR; dist; NORM_MUL] THEN
  MATCH_MP_TAC(MATCH_MP (REWRITE_RULE[IMP_CONJ] REAL_LET_TRANS)
   (SPEC_ALL NORM_LE_L1)) THEN
  SIMP_TAC[LAMBDA_BETA; VECTOR_SUB_COMPONENT; VECTOR_MUL_COMPONENT] THEN
  MATCH_MP_TAC REAL_LET_TRANS THEN
  EXISTS_TAC `&(dimindex(:N)) * inv(&2 pow n)` THEN ASM_REWRITE_TAC[] THEN
  GEN_REWRITE_TAC (RAND_CONV o LAND_CONV o RAND_CONV) [GSYM CARD_NUMSEG_1] THEN
  MATCH_MP_TAC SUM_BOUND THEN REWRITE_TAC[FINITE_NUMSEG; IN_NUMSEG] THEN
  X_GEN_TAC `k:num` THEN STRIP_TAC THEN
  GEN_REWRITE_TAC RAND_CONV [GSYM REAL_MUL_RID] THEN
  SIMP_TAC[REAL_ABS_MUL; REAL_POW_EQ_0; REAL_OF_NUM_EQ; ARITH;
    REAL_FIELD `~(a = &0) ==> inv a * b - x = inv a * (b - a * x)`] THEN
  MATCH_MP_TAC REAL_LE_MUL2 THEN REWRITE_TAC[REAL_ABS_POS] THEN
  REWRITE_TAC[REAL_LE_REFL; REAL_ABS_POW; REAL_ABS_INV; REAL_ABS_NUM] THEN
  MP_TAC(SPEC `&2 pow n * (x:real^N)$k` FLOOR) THEN REAL_ARITH_TAC);;


let CLOSURE_RATIONAL_COORDINATES = 
prove
 (`closure { x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i) } =
   (:real^N)`,

  MATCH_MP_TAC(SET_RULE `!s. s SUBSET t /\ s = UNIV ==> t = UNIV`) THEN
  EXISTS_TAC
   `closure { inv(&2 pow n) % x:real^N |n,x|
              !i. 1 <= i /\ i <= dimindex(:N) ==> integer(x$i) }` THEN

  CONJ_TAC THENL [ALL_TAC; REWRITE_TAC[CLOSURE_DYADIC_RATIONALS]] THEN
  MATCH_MP_TAC SUBSET_CLOSURE THEN
  REWRITE_TAC[SUBSET; FORALL_IN_GSPEC; IN_ELIM_THM; VECTOR_MUL_COMPONENT] THEN
  ASM_SIMP_TAC[RATIONAL_CLOSED]);;


let CLOSURE_DYADIC_RATIONALS_IN_OPEN_SET = 
prove
 (`!s:real^N->bool.
        open s
        ==> closure(s INTER
                    { inv(&2 pow n) % x | n,x |
                      !i. 1 <= i /\ i <= dimindex(:N) ==> integer(x$i) }) =
            closure s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSURE_OPEN_INTER_SUPERSET THEN
  ASM_REWRITE_TAC[CLOSURE_DYADIC_RATIONALS; SUBSET_UNIV]);;


let CLOSURE_RATIONALS_IN_OPEN_SET = 
prove
 (`!s:real^N->bool.
        open s
        ==> closure(s INTER
                    { inv(&2 pow n) % x | n,x |
                      !i. 1 <= i /\ i <= dimindex(:N) ==> integer(x$i) }) =
            closure s`,

  REPEAT STRIP_TAC THEN MATCH_MP_TAC CLOSURE_OPEN_INTER_SUPERSET THEN
  ASM_REWRITE_TAC[CLOSURE_DYADIC_RATIONALS; SUBSET_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Various separability-type properties.                                     *)
(* ------------------------------------------------------------------------- *)


let UNIV_SECOND_COUNTABLE = 
prove
 (`?b. COUNTABLE b /\ (!c. c IN b ==> open c) /\
       !s:real^N->bool. open s ==> ?u. u SUBSET b /\ s = UNIONS u`,

  EXISTS_TAC
   `IMAGE (\(v:real^N,q). ball(v,q))
          ({v | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(v$i)} CROSS
           rational)` THEN
  REPEAT CONJ_TAC THENL
   [MATCH_MP_TAC COUNTABLE_IMAGE THEN MATCH_MP_TAC COUNTABLE_CROSS THEN
    REWRITE_TAC[COUNTABLE_RATIONAL] THEN MATCH_MP_TAC COUNTABLE_CART THEN
    REWRITE_TAC[COUNTABLE_RATIONAL; SET_RULE `{x | P x} = P`];
    REWRITE_TAC[FORALL_IN_IMAGE; CROSS; FORALL_IN_GSPEC; OPEN_BALL];
    REPEAT STRIP_TAC THEN
    ASM_CASES_TAC `s:real^N->bool = {}` THENL
     [EXISTS_TAC `{}:(real^N->bool)->bool` THEN
      ASM_REWRITE_TAC[UNIONS_0; EMPTY_SUBSET];
      ALL_TAC] THEN
    EXISTS_TAC `{c | c IN IMAGE (\(v:real^N,q). ball(v,q))
          ({v | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(v$i)} CROSS
           rational) /\ c SUBSET s}` THEN
    CONJ_TAC THENL [SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC SUBSET_ANTISYM THEN CONJ_TAC THENL [ALL_TAC; SET_TAC[]] THEN
    REWRITE_TAC[SUBSET; IN_UNIONS; IN_ELIM_THM] THEN
    REWRITE_TAC[GSYM CONJ_ASSOC; EXISTS_IN_IMAGE] THEN
    REWRITE_TAC[CROSS; EXISTS_PAIR_THM; EXISTS_IN_GSPEC] THEN
    REWRITE_TAC[IN_ELIM_PAIR_THM] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [OPEN_CONTAINS_BALL]) THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
    ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM; SUBSET; IN_BALL] THEN
    X_GEN_TAC `e:real` THEN STRIP_TAC THEN REWRITE_TAC[IN_ELIM_THM] THEN
    MP_TAC(REWRITE_RULE[EXTENSION; IN_UNIV] CLOSURE_RATIONAL_COORDINATES) THEN
    REWRITE_TAC[CLOSURE_APPROACHABLE] THEN
    DISCH_THEN(MP_TAC o SPECL [`x:real^N`; `e / &4`]) THEN
    ANTS_TAC THENL [ASM_REAL_ARITH_TAC; REWRITE_TAC[IN_ELIM_THM]] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
    SUBGOAL_THEN `?x. rational x /\ e / &3 < x /\ x < e / &2`
     (X_CHOOSE_THEN `q:real` STRIP_ASSUME_TAC)
    THENL
     [MP_TAC(ISPECL [`&5 / &12 * e`; `e / &12`] RATIONAL_APPROXIMATION) THEN
      ANTS_TAC THENL [ASM_REAL_ARITH_TAC; MATCH_MP_TAC MONO_EXISTS] THEN
      SIMP_TAC[] THEN REAL_ARITH_TAC;
      EXISTS_TAC `q:real` THEN ASM_REWRITE_TAC[] THEN REPEAT CONJ_TAC THENL
       [ASM_REWRITE_TAC[IN];
        REPEAT STRIP_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
        REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC;
        ASM_REAL_ARITH_TAC]]]);;


let UNIV_SECOND_COUNTABLE_SEQUENCE = 
prove
 (`?b:num->real^N->bool.
        (!m n. b m = b n <=> m = n) /\
        (!n. open(b n)) /\
        (!s. open s ==> ?k. s = UNIONS {b n | n IN k})`,

  X_CHOOSE_THEN `bb:(real^N->bool)->bool` STRIP_ASSUME_TAC
    UNIV_SECOND_COUNTABLE THEN
  MP_TAC(ISPEC `bb:(real^N->bool)->bool` COUNTABLE_AS_INJECTIVE_IMAGE) THEN
  ANTS_TAC THENL
   [ASM_REWRITE_TAC[INFINITE] THEN DISCH_TAC THEN
    SUBGOAL_THEN
     `INFINITE {ball(vec 0:real^N,inv(&n + &1)) | n IN (:num)}`
    MP_TAC THENL
     [REWRITE_TAC[SIMPLE_IMAGE] THEN MATCH_MP_TAC(REWRITE_RULE
       [RIGHT_IMP_FORALL_THM; IMP_IMP] INFINITE_IMAGE_INJ) THEN
      REWRITE_TAC[num_INFINITE] THEN MATCH_MP_TAC WLOG_LT THEN SIMP_TAC[] THEN
      CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
      MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN DISCH_TAC THEN
      REWRITE_TAC[EXTENSION] THEN
      DISCH_THEN(MP_TAC o SPEC `inv(&n + &1) % basis 1:real^N`) THEN
      REWRITE_TAC[IN_BALL; DIST_0; NORM_MUL; REAL_ABS_INV] THEN
      SIMP_TAC[NORM_BASIS; DIMINDEX_GE_1; LE_REFL; REAL_MUL_RID] THEN
      ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN DISCH_TAC THEN
      REWRITE_TAC[REAL_ARITH `abs(&n + &1) = &n + &1`; REAL_LT_REFL] THEN
      MATCH_MP_TAC REAL_LT_INV2 THEN
      REWRITE_TAC[REAL_OF_NUM_LT; REAL_OF_NUM_ADD] THEN ASM_ARITH_TAC;
      REWRITE_TAC[INFINITE; SIMPLE_IMAGE] THEN
      MATCH_MP_TAC FINITE_SUBSET THEN
      EXISTS_TAC `IMAGE UNIONS {u | u SUBSET bb} :(real^N->bool)->bool` THEN
      ASM_SIMP_TAC[FINITE_IMAGE; FINITE_POWERSET] THEN
      GEN_REWRITE_TAC I [SUBSET] THEN SIMP_TAC[FORALL_IN_IMAGE; IN_UNIV] THEN
      X_GEN_TAC `n:num` THEN REWRITE_TAC[IN_IMAGE; IN_ELIM_THM] THEN
      ASM_MESON_TAC[OPEN_BALL]];
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:num->real^N->bool` THEN
    DISCH_THEN(CONJUNCTS_THEN2 SUBST_ALL_TAC ASSUME_TAC) THEN
    RULE_ASSUM_TAC(REWRITE_RULE[FORALL_IN_IMAGE; IN_UNIV]) THEN
    REPEAT(CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC]) THEN
    X_GEN_TAC `s:real^N->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `s:real^N->bool`) THEN
    ASM_REWRITE_TAC[SUBSET_IMAGE; LEFT_AND_EXISTS_THM; SUBSET_UNIV] THEN
    ONCE_REWRITE_TAC[SWAP_EXISTS_THM] THEN MATCH_MP_TAC MONO_EXISTS THEN
    REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[SIMPLE_IMAGE]]);;


let SUBSET_SECOND_COUNTABLE = 
prove
 (`!s:real^N->bool.
       ?b. COUNTABLE b /\
           (!c. c IN b ==> ~(c = {}) /\ open_in(subtopology euclidean s) c) /\
           !t. open_in(subtopology euclidean s) t
               ==> ?u. u SUBSET b /\ t = UNIONS u`,

  GEN_TAC THEN
  SUBGOAL_THEN
   `?b. COUNTABLE b /\
           (!c:real^N->bool. c IN b ==> open_in(subtopology euclidean s) c) /\
           !t. open_in(subtopology euclidean s) t
               ==> ?u. u SUBSET b /\ t = UNIONS u`
  STRIP_ASSUME_TAC THENL
   [X_CHOOSE_THEN `B:(real^N->bool)->bool` STRIP_ASSUME_TAC
      UNIV_SECOND_COUNTABLE THEN
    EXISTS_TAC `{s INTER c :real^N->bool | c IN B}` THEN
    ASM_SIMP_TAC[SIMPLE_IMAGE; COUNTABLE_IMAGE] THEN
    ASM_SIMP_TAC[FORALL_IN_IMAGE; EXISTS_SUBSET_IMAGE; OPEN_IN_OPEN_INTER] THEN
    REWRITE_TAC[OPEN_IN_OPEN] THEN
    X_GEN_TAC `t:real^N->bool` THEN
    DISCH_THEN(X_CHOOSE_THEN `u:real^N->bool` STRIP_ASSUME_TAC) THEN
    FIRST_X_ASSUM SUBST_ALL_TAC THEN
    SUBGOAL_THEN `?b. b SUBSET B /\ u:real^N->bool = UNIONS b`
    STRIP_ASSUME_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
    FIRST_X_ASSUM SUBST_ALL_TAC THEN
    EXISTS_TAC `b:(real^N->bool)->bool` THEN ASM_REWRITE_TAC[] THEN
    REWRITE_TAC[INTER_UNIONS] THEN AP_TERM_TAC THEN SET_TAC[];
    EXISTS_TAC `b DELETE ({}:real^N->bool)` THEN
    ASM_SIMP_TAC[COUNTABLE_DELETE; IN_DELETE; SUBSET_DELETE] THEN
    X_GEN_TAC `t:real^N->bool` THEN DISCH_THEN(ANTE_RES_THEN MP_TAC) THEN
    DISCH_THEN(X_CHOOSE_THEN `u:(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `u DELETE ({}:real^N->bool)` THEN
    REPEAT(CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC]) THEN
    FIRST_X_ASSUM SUBST_ALL_TAC THEN
    REWRITE_TAC[EXTENSION; IN_UNIONS] THEN
    GEN_TAC THEN AP_TERM_TAC THEN ABS_TAC THEN
    REWRITE_TAC[IN_DELETE] THEN SET_TAC[]]);;


let SEPARABLE = 
prove
 (`!s:real^N->bool.
        ?t. COUNTABLE t /\ t SUBSET s /\ s SUBSET closure t`,

  MP_TAC SUBSET_SECOND_COUNTABLE THEN
  MATCH_MP_TAC MONO_FORALL THEN X_GEN_TAC `s:real^N->bool` THEN
  REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; LEFT_AND_EXISTS_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `B:(real^N->bool)->bool`
   (CONJUNCTS_THEN2 ASSUME_TAC (CONJUNCTS_THEN2 MP_TAC ASSUME_TAC))) THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `f:(real^N->bool)->real^N` THEN DISCH_TAC THEN
  EXISTS_TAC `IMAGE (f:(real^N->bool)->real^N) B` THEN
  ASM_SIMP_TAC[COUNTABLE_IMAGE] THEN CONJ_TAC THENL
   [REWRITE_TAC[SUBSET; FORALL_IN_IMAGE] THEN
    X_GEN_TAC `c:real^N->bool` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N->bool`) THEN
    ASM_REWRITE_TAC[] THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o MATCH_MP OPEN_IN_SUBSET) THEN
    REWRITE_TAC[TOPSPACE_SUBTOPOLOGY; TOPSPACE_EUCLIDEAN] THEN ASM SET_TAC[];
    REWRITE_TAC[SUBSET; CLOSURE_APPROACHABLE; EXISTS_IN_IMAGE] THEN
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    UNDISCH_THEN
     `!t:real^N->bool.
        open_in (subtopology euclidean s) t
        ==> (?u. u SUBSET B /\ t = UNIONS u)`
     (MP_TAC o SPEC `s INTER ball(x:real^N,e)`) THEN
    SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_BALL; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `b:(real^N->bool)->bool` THEN
    ASM_CASES_TAC `b:(real^N->bool)->bool = {}` THENL
     [MATCH_MP_TAC(TAUT `~b ==> a /\ b ==> c`) THEN
      ASM_REWRITE_TAC[EXTENSION; IN_INTER; NOT_IN_EMPTY; UNIONS_0] THEN
      ASM_MESON_TAC[CENTRE_IN_BALL];
      STRIP_TAC THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `c:real^N->bool` THEN
      DISCH_TAC THEN CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [EXTENSION]) THEN
      DISCH_THEN(MP_TAC o SPEC `(f:(real^N->bool)->real^N) c`) THEN
      ONCE_REWRITE_TAC[DIST_SYM] THEN REWRITE_TAC[IN_INTER; IN_BALL] THEN
      MATCH_MP_TAC(TAUT `a /\ c ==> (a /\ b <=> c) ==> b`) THEN
      CONJ_TAC THENL [ALL_TAC; ASM SET_TAC[]] THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `c:real^N->bool`) THEN
      ANTS_TAC THENL [ASM SET_TAC[]; STRIP_TAC] THEN
      FIRST_X_ASSUM(MP_TAC o MATCH_MP OPEN_IN_SUBSET) THEN
      REWRITE_TAC[TOPSPACE_SUBTOPOLOGY; TOPSPACE_EUCLIDEAN] THEN
      ASM SET_TAC[]]]);;


let OPEN_SET_RATIONAL_COORDINATES = 
prove
 (`!s. open s /\ ~(s = {})
       ==> ?x:real^N. x IN s /\
                      !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i)`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `~(closure { x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i) } INTER
    (s:real^N->bool) = {})`
  MP_TAC THENL
   [ASM_REWRITE_TAC[CLOSURE_RATIONAL_COORDINATES; INTER_UNIV]; ALL_TAC] THEN
  REWRITE_TAC[GSYM MEMBER_NOT_EMPTY; CLOSURE_APPROACHABLE; IN_INTER;
              IN_ELIM_THM] THEN
  DISCH_THEN(X_CHOOSE_THEN `a:real^N` STRIP_ASSUME_TAC) THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `a:real^N` o REWRITE_RULE[open_def]) THEN
  ASM_REWRITE_TAC[] THEN ASM_MESON_TAC[]);;

let OPEN_COUNTABLE_UNION_OPEN_INTERVALS,
    OPEN_COUNTABLE_UNION_CLOSED_INTERVALS = (CONJ_PAIR o prove)
 (`(!s:real^N->bool.
        open s
        ==> ?D. COUNTABLE D /\
                (!i. i IN D ==> i SUBSET s /\ ?a b. i = interval(a,b)) /\
                UNIONS D = s) /\
   (!s:real^N->bool.
        open s
        ==> ?D. COUNTABLE D /\
                (!i. i IN D ==> i SUBSET s /\ ?a b. i = interval[a,b]) /\
                UNIONS D = s)`,
  REPEAT STRIP_TAC THENL
   [EXISTS_TAC
     `{i | i IN IMAGE (\(a:real^N,b). interval(a,b))
            ({x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i)} CROSS
             {x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i)}) /\
           i SUBSET s}`;
    EXISTS_TAC
     `{i | i IN IMAGE (\(a:real^N,b). interval[a,b])
            ({x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i)} CROSS
             {x | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i)}) /\
           i SUBSET s}`] THEN
  (SIMP_TAC[COUNTABLE_RESTRICT; COUNTABLE_IMAGE; COUNTABLE_CROSS;
           COUNTABLE_RATIONAL_COORDINATES] THEN
   REWRITE_TAC[IN_ELIM_THM; UNIONS_GSPEC; IMP_CONJ; GSYM CONJ_ASSOC] THEN
   REWRITE_TAC[FORALL_IN_IMAGE; EXISTS_IN_IMAGE] THEN
   REWRITE_TAC[FORALL_PAIR_THM; EXISTS_PAIR_THM; IN_CROSS; IN_ELIM_THM] THEN
   CONJ_TAC THENL [MESON_TAC[]; ALL_TAC] THEN
   REWRITE_TAC[EXTENSION; IN_ELIM_THM] THEN
   X_GEN_TAC `x:real^N` THEN EQ_TAC THENL [SET_TAC[]; DISCH_TAC] THEN
   FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N` o REWRITE_RULE[open_def]) THEN
   ASM_REWRITE_TAC[] THEN
   DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
   SUBGOAL_THEN
    `!i. 1 <= i /\ i <= dimindex(:N)
         ==> ?a b. rational a /\ rational b /\
                   a < (x:real^N)$i /\ (x:real^N)$i < b /\
                   abs(b - a) < e / &(dimindex(:N))`
   MP_TAC THENL
    [REPEAT STRIP_TAC THEN MATCH_MP_TAC RATIONAL_APPROXIMATION_STRADDLE THEN
     ASM_SIMP_TAC[REAL_LT_DIV; REAL_OF_NUM_LT; LE_1; DIMINDEX_GE_1];
     REWRITE_TAC[LAMBDA_SKOLEM]] THEN
   MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `a:real^N` THEN
   MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `b:real^N` THEN
   DISCH_TAC THEN ASM_SIMP_TAC[SUBSET; IN_INTERVAL; REAL_LT_IMP_LE] THEN
   X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
   REWRITE_TAC[dist] THEN MP_TAC(ISPEC `y - x:real^N` NORM_LE_L1) THEN
   MATCH_MP_TAC(REAL_ARITH `s < e ==> n <= s ==> n < e`) THEN
   MATCH_MP_TAC SUM_BOUND_LT_GEN THEN
   REWRITE_TAC[FINITE_NUMSEG; NUMSEG_EMPTY; NOT_LT; CARD_NUMSEG_1] THEN
   REWRITE_TAC[DIMINDEX_GE_1; IN_NUMSEG; VECTOR_SUB_COMPONENT] THEN
   X_GEN_TAC `k:num` THEN STRIP_TAC THEN
   REPEAT(FIRST_X_ASSUM(MP_TAC o SPEC `k:num`)) THEN ASM_REWRITE_TAC[] THEN
   ASM_REAL_ARITH_TAC));;


let LINDELOF = 
prove
 (`!f:(real^N->bool)->bool.
        (!s. s IN f ==> open s)
        ==> ?f'. f' SUBSET f /\ COUNTABLE f' /\ UNIONS f' = UNIONS f`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `?b. COUNTABLE b /\
        (!c:real^N->bool. c IN b ==> open c) /\
        (!s. open s ==> ?u. u SUBSET b /\ s = UNIONS u)`
  STRIP_ASSUME_TAC THENL [ASM_REWRITE_TAC[UNIV_SECOND_COUNTABLE]; ALL_TAC] THEN
  ABBREV_TAC
   `d = {s:real^N->bool | s IN b /\ ?u. u IN f /\ s SUBSET u}` THEN
  SUBGOAL_THEN
   `COUNTABLE d /\ UNIONS f :real^N->bool = UNIONS d`
  STRIP_ASSUME_TAC THENL
   [EXPAND_TAC "d" THEN ASM_SIMP_TAC[COUNTABLE_RESTRICT] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!s:real^N->bool. ?u. s IN d ==> u IN f /\ s SUBSET u`
  MP_TAC THENL [EXPAND_TAC "d" THEN SET_TAC[]; ALL_TAC] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `g:(real^N->bool)->(real^N->bool)` THEN STRIP_TAC THEN
  EXISTS_TAC `IMAGE (g:(real^N->bool)->(real^N->bool)) d` THEN
  ASM_SIMP_TAC[COUNTABLE_IMAGE; UNIONS_IMAGE] THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE] THEN ASM SET_TAC[]);;


let LINDELOF_OPEN_IN = 
prove
 (`!f u:real^N->bool.
        (!s. s IN f ==> open_in (subtopology euclidean u) s)
        ==> ?f'. f' SUBSET f /\ COUNTABLE f' /\ UNIONS f' = UNIONS f`,

  REPEAT GEN_TAC THEN REWRITE_TAC[OPEN_IN_OPEN] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `v:(real^N->bool)->real^N->bool` THEN DISCH_TAC THEN
  MP_TAC(ISPEC `IMAGE (v:(real^N->bool)->real^N->bool) f` LINDELOF) THEN
  ASM_SIMP_TAC[FORALL_IN_IMAGE] THEN
  ONCE_REWRITE_TAC[TAUT `p /\ q /\ r <=> q /\ p /\ r`] THEN
  REWRITE_TAC[EXISTS_COUNTABLE_SUBSET_IMAGE] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `f':(real^N->bool)->bool` THEN
  STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
  SUBGOAL_THEN
  `!f'. f' SUBSET f ==> UNIONS f' = (u:real^N->bool) INTER UNIONS (IMAGE v f')`
  MP_TAC THENL [ASM SET_TAC[]; ASM_SIMP_TAC[SUBSET_REFL]]);;


let COUNTABLE_DISJOINT_OPEN_SUBSETS = 
prove
 (`!f. (!s:real^N->bool. s IN f ==> open s) /\ pairwise DISJOINT f
       ==> COUNTABLE f`,

  REPEAT STRIP_TAC THEN FIRST_ASSUM(MP_TAC o MATCH_MP LINDELOF) THEN
  DISCH_THEN(X_CHOOSE_THEN `g:(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
  MATCH_MP_TAC COUNTABLE_SUBSET THEN
  EXISTS_TAC `({}:real^N->bool) INSERT g` THEN
  ASM_REWRITE_TAC[COUNTABLE_INSERT] THEN
  REWRITE_TAC[SUBSET; IN_INSERT] THEN
  REPEAT(POP_ASSUM MP_TAC) THEN
  REWRITE_TAC[EXTENSION; SUBSET] THEN
  REWRITE_TAC[IN_UNIONS; pairwise] THEN
  REWRITE_TAC[SET_RULE `DISJOINT s t <=> !x. ~(x IN s /\ x IN t)`] THEN
  REWRITE_TAC[NOT_IN_EMPTY] THEN MESON_TAC[]);;


let CARD_EQ_OPEN_SETS = 
prove
 (`{s:real^N->bool | open s} =_c (:real)`,

  REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [X_CHOOSE_THEN `b:(real^N->bool)->bool` STRIP_ASSUME_TAC
      UNIV_SECOND_COUNTABLE THEN
    TRANS_TAC CARD_LE_TRANS `{s:(real^N->bool)->bool | s SUBSET b}` THEN
    CONJ_TAC THENL
     [REWRITE_TAC[LE_C] THEN
      EXISTS_TAC `UNIONS:((real^N->bool)->bool)->real^N->bool` THEN
      REWRITE_TAC[IN_ELIM_THM] THEN ASM_MESON_TAC[];
      TRANS_TAC CARD_LE_TRANS `{s | s SUBSET (:num)}` THEN CONJ_TAC THENL
       [MATCH_MP_TAC CARD_LE_POWERSET THEN ASM_REWRITE_TAC[GSYM COUNTABLE_ALT];
        REWRITE_TAC[SUBSET_UNIV; UNIV_GSPEC] THEN
        MESON_TAC[CARD_EQ_IMP_LE; CARD_EQ_SYM; CARD_EQ_REAL]]];
    REWRITE_TAC[le_c; IN_UNIV; IN_ELIM_THM] THEN
    EXISTS_TAC `\x. ball(x % basis 1:real^N,&1)` THEN
    REWRITE_TAC[OPEN_BALL; GSYM SUBSET_ANTISYM_EQ; SUBSET_BALLS] THEN
    CONV_TAC REAL_RAT_REDUCE_CONV THEN
    REWRITE_TAC[NORM_ARITH `dist(p:real^N,q) + &1 <= &1 <=> p = q`] THEN
    REWRITE_TAC[VECTOR_MUL_RCANCEL; EQ_SYM_EQ] THEN
    SIMP_TAC[BASIS_NONZERO; DIMINDEX_GE_1; ARITH]]);;


let CARD_EQ_CLOSED_SETS = 
prove
 (`{s:real^N->bool | closed s} =_c (:real)`,

  SUBGOAL_THEN
   `{s:real^N->bool | closed s} =
    IMAGE (\s. (:real^N) DIFF s) {s | open s}`
  SUBST1_TAC THENL
   [CONV_TAC SYM_CONV THEN MATCH_MP_TAC SURJECTIVE_IMAGE_EQ THEN
    REWRITE_TAC[IN_ELIM_THM; GSYM OPEN_CLOSED] THEN
    MESON_TAC[SET_RULE `UNIV DIFF (UNIV DIFF s) = s`];
    TRANS_TAC CARD_EQ_TRANS `{s:real^N->bool | open s}` THEN
    REWRITE_TAC[CARD_EQ_OPEN_SETS] THEN
    MATCH_MP_TAC CARD_EQ_IMAGE THEN SET_TAC[]]);;


let CARD_EQ_COMPACT_SETS = 
prove
 (`{s:real^N->bool | compact s} =_c (:real)`,

  REWRITE_TAC[GSYM CARD_LE_ANTISYM] THEN CONJ_TAC THENL
   [TRANS_TAC CARD_LE_TRANS `{s:real^N->bool | closed s}` THEN
    SIMP_TAC[CARD_EQ_IMP_LE; CARD_EQ_CLOSED_SETS] THEN
    MATCH_MP_TAC CARD_LE_SUBSET THEN
    SIMP_TAC[SUBSET; IN_ELIM_THM; COMPACT_IMP_CLOSED];
    REWRITE_TAC[le_c; IN_UNIV; IN_ELIM_THM] THEN
    EXISTS_TAC `\x. {x % basis 1:real^N}` THEN
    REWRITE_TAC[COMPACT_SING; SET_RULE `{x} = {y} <=> x = y`] THEN
    SIMP_TAC[VECTOR_MUL_RCANCEL; BASIS_NONZERO; DIMINDEX_GE_1; ARITH]]);;


let COUNTABLE_NON_CONDENSATION_POINTS = 
prove
 (`!s:real^N->bool. COUNTABLE(s DIFF {x | x condensation_point_of s})`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[condensation_point_of] THEN
  MATCH_MP_TAC COUNTABLE_SUBSET THEN
  X_CHOOSE_THEN `b:(real^N->bool)->bool` STRIP_ASSUME_TAC
   UNIV_SECOND_COUNTABLE THEN
  EXISTS_TAC
   `s INTER UNIONS { u:real^N->bool | u IN b /\ COUNTABLE(s INTER u)}` THEN
  REWRITE_TAC[INTER_UNIONS; IN_ELIM_THM] THEN CONJ_TAC THENL
   [MATCH_MP_TAC COUNTABLE_UNIONS THEN SIMP_TAC[FORALL_IN_GSPEC] THEN
    ONCE_REWRITE_TAC[SIMPLE_IMAGE_GEN] THEN
    ASM_SIMP_TAC[COUNTABLE_IMAGE; COUNTABLE_RESTRICT];
    SIMP_TAC[SUBSET; UNIONS_GSPEC; IN_ELIM_THM; IN_INTER; IN_DIFF] THEN
    X_GEN_TAC `x:real^N` THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    REWRITE_TAC[NOT_FORALL_THM; NOT_IMP; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THEN
    SUBGOAL_THEN `?u:real^N->bool. x IN u /\ u IN b /\ u SUBSET t` MP_TAC THENL
     [ASM SET_TAC[]; MATCH_MP_TAC MONO_EXISTS] THEN
    REPEAT STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC COUNTABLE_SUBSET THEN
    EXISTS_TAC `s INTER t:real^N->bool` THEN ASM SET_TAC[]]);;


let CARD_EQ_CONDENSATION_POINTS_IN_SET = 
prove
 (`!s:real^N->bool.
     ~(COUNTABLE s) ==> {x | x IN s /\ x condensation_point_of s} =_c s`,

  REPEAT STRIP_TAC THEN
  TRANS_TAC CARD_EQ_TRANS
   `(s DIFF {x | x condensation_point_of s}) +_c
    {x:real^N | x IN s /\ x condensation_point_of s}` THEN
  CONJ_TAC THENL
   [ONCE_REWRITE_TAC[CARD_EQ_SYM] THEN MATCH_MP_TAC CARD_ADD_ABSORB THEN
    MATCH_MP_TAC(TAUT `p /\ (p ==> q) ==> p /\ q`) THEN CONJ_TAC THENL
     [POP_ASSUM MP_TAC THEN REWRITE_TAC[INFINITE; CONTRAPOS_THM] THEN
      DISCH_THEN(MP_TAC o CONJ (SPEC `s:real^N->bool`
       COUNTABLE_NON_CONDENSATION_POINTS) o MATCH_MP FINITE_IMP_COUNTABLE) THEN
      REWRITE_TAC[GSYM COUNTABLE_UNION] THEN MATCH_MP_TAC EQ_IMP THEN
      AP_TERM_TAC THEN SET_TAC[];
      REWRITE_TAC[INFINITE_CARD_LE] THEN
      MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] CARD_LE_TRANS) THEN
      REWRITE_TAC[GSYM COUNTABLE_ALT; COUNTABLE_NON_CONDENSATION_POINTS]];
    ONCE_REWRITE_TAC[CARD_EQ_SYM] THEN
    W(MP_TAC o PART_MATCH (rand o rand) CARD_DISJOINT_UNION o rand o snd) THEN
    ANTS_TAC THENL [SET_TAC[]; ALL_TAC] THEN
    MATCH_MP_TAC EQ_IMP THEN AP_THM_TAC THEN AP_TERM_TAC THEN SET_TAC[]]);;

let LIMPT_OF_CONDENSATION_POINTS,CONDENSATION_POINT_OF_CONDENSATION_POINTS =
  (CONJ_PAIR o prove)
 (`(!x:real^N s.
        x limit_point_of {y | y condensation_point_of s} <=>
        x condensation_point_of s) /\
   (!x:real^N s.
        x condensation_point_of {y | y condensation_point_of s} <=>
        x condensation_point_of s)`,
  REWRITE_TAC[AND_FORALL_THM] THEN REPEAT GEN_TAC THEN MATCH_MP_TAC(TAUT
   `(r ==> q) /\ (q ==> p) /\ (p ==> r)
    ==> (q <=> p) /\ (r <=> p)`) THEN
  REWRITE_TAC[CONDENSATION_POINT_IMP_LIMPT] THEN CONJ_TAC THENL
   [REWRITE_TAC[LIMPT_APPROACHABLE; CONDENSATION_POINT_INFINITE_BALL] THEN
    REPEAT GEN_TAC THEN REWRITE_TAC[IN_ELIM_THM] THEN DISCH_TAC THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
    DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC) THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
    ASM_REWRITE_TAC[REAL_HALF; CONTRAPOS_THM] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] COUNTABLE_SUBSET) THEN
    SIMP_TAC[SUBSET; IN_INTER; IN_BALL] THEN
    REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC;
    ONCE_REWRITE_TAC[CONDENSATION_POINT_INFINITE_BALL] THEN DISCH_TAC THEN
    X_GEN_TAC `e:real` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `e / &2`) THEN
    ASM_REWRITE_TAC[REAL_HALF] THEN DISCH_THEN(MP_TAC o MATCH_MP
     (MESON[CARD_EQ_CONDENSATION_POINTS_IN_SET; CARD_COUNTABLE_CONG]
        `~COUNTABLE s
         ==> ~COUNTABLE {x | x IN s /\ x condensation_point_of s}`)) THEN
    REWRITE_TAC[UNCOUNTABLE_REAL; CONTRAPOS_THM] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] COUNTABLE_SUBSET) THEN
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_INTER] THEN X_GEN_TAC `y:real^N` THEN
    REPEAT STRIP_TAC THENL
     [ASM_MESON_TAC[CONDENSATION_POINT_OF_SUBSET; INTER_SUBSET]; ALL_TAC] THEN
    MATCH_MP_TAC(SET_RULE `!s. x IN s /\ s SUBSET t ==> x IN t`) THEN
    EXISTS_TAC `closure(s INTER ball(x:real^N,e / &2))` THEN CONJ_TAC THENL
     [REWRITE_TAC[closure; IN_UNION; IN_ELIM_THM] THEN DISJ2_TAC THEN
      ASM_SIMP_TAC[CONDENSATION_POINT_IMP_LIMPT];
      TRANS_TAC SUBSET_TRANS `closure(ball(x:real^N,e / &2))` THEN
      SIMP_TAC[SUBSET_CLOSURE; INTER_SUBSET] THEN
      ASM_SIMP_TAC[CLOSURE_BALL; REAL_HALF; SUBSET_BALLS; DIST_REFL] THEN
      ASM_REAL_ARITH_TAC]]);;


let CLOSED_CONDENSATION_POINTS = 
prove
 (`!s:real^N->bool. closed {x | x condensation_point_of s}`,

  SIMP_TAC[CLOSED_LIMPT; LIMPT_OF_CONDENSATION_POINTS; IN_ELIM_THM]);;


let CANTOR_BENDIXSON = 
prove
 (`!s:real^N->bool.
        closed s
        ==> ?t u. closed t /\ (!x. x IN t ==> x limit_point_of t) /\
                  COUNTABLE u /\ s = t UNION u`,

  REPEAT STRIP_TAC THEN MAP_EVERY EXISTS_TAC
   [`{x:real^N | x condensation_point_of s}`;
    `s DIFF {x:real^N | x condensation_point_of s}`] THEN
  REWRITE_TAC[COUNTABLE_NON_CONDENSATION_POINTS; CLOSED_CONDENSATION_POINTS;
              IN_ELIM_THM; LIMPT_OF_CONDENSATION_POINTS] THEN
  REWRITE_TAC[SET_RULE `s = t UNION (s DIFF t) <=> t SUBSET s`] THEN
  RULE_ASSUM_TAC(REWRITE_RULE[CLOSED_LIMPT]) THEN
  REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN
  ASM_MESON_TAC[CONDENSATION_POINT_IMP_LIMPT]);;

(* ------------------------------------------------------------------------- *)
(* A discrete set is countable, and an uncountable set has a limit point.    *)
(* ------------------------------------------------------------------------- *)


let DISCRETE_IMP_COUNTABLE = 
prove
 (`!s:real^N->bool.
        (!x. x IN s ==> ?e. &0 < e /\
                            !y. y IN s /\ ~(y = x) ==> e <= norm(y - x))
        ==> COUNTABLE s`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `!x. x IN s
        ==> ?q. (!i. 1 <= i /\ i <= dimindex(:N) ==> rational(q$i)) /\
                !y:real^N. y IN s /\ ~(y = x) ==> norm(x - q) < norm(y - q)`
  MP_TAC THENL
   [X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
    MP_TAC(SET_RULE `x IN (:real^N)`) THEN
    REWRITE_TAC[GSYM CLOSURE_RATIONAL_COORDINATES] THEN
    REWRITE_TAC[CLOSURE_APPROACHABLE; IN_ELIM_THM] THEN
    DISCH_THEN(MP_TAC o SPEC `e / &2`) THEN ASM_REWRITE_TAC[REAL_HALF] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `q:real^N` THEN
    STRIP_TAC THEN ASM_REWRITE_TAC[] THEN
    X_GEN_TAC `y:real^N` THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `y:real^N`) THEN ASM_REWRITE_TAC[] THEN
    REPEAT(POP_ASSUM MP_TAC) THEN NORM_ARITH_TAC;
    POP_ASSUM(K ALL_TAC) THEN
    REWRITE_TAC[RIGHT_IMP_EXISTS_THM; SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
    X_GEN_TAC `q:real^N->real^N` THEN DISCH_TAC THEN
    MP_TAC(ISPECL
     [`s:real^N->bool`;
      `{ x:real^N | !i. 1 <= i /\ i <= dimindex(:N) ==> rational(x$i) }`;
      `(:num)`] CARD_LE_TRANS) THEN
    REWRITE_TAC[COUNTABLE; ge_c] THEN DISCH_THEN MATCH_MP_TAC THEN
    SIMP_TAC[REWRITE_RULE[COUNTABLE; ge_c] COUNTABLE_RATIONAL_COORDINATES] THEN
    REWRITE_TAC[le_c] THEN EXISTS_TAC `q:real^N->real^N` THEN
    ASM_SIMP_TAC[IN_ELIM_THM] THEN ASM_MESON_TAC[REAL_LT_ANTISYM]]);;


let UNCOUNTABLE_CONTAINS_LIMIT_POINT = 
prove
 (`!s. ~(COUNTABLE s) ==> ?x. x IN s /\ x limit_point_of s`,

  GEN_TAC THEN DISCH_THEN(MP_TAC o MATCH_MP
   (ONCE_REWRITE_RULE[GSYM CONTRAPOS_THM] DISCRETE_IMP_COUNTABLE)) THEN
  REWRITE_TAC[LIMPT_APPROACHABLE; GSYM REAL_NOT_LT; dist] THEN
  MESON_TAC[]);;

(* ------------------------------------------------------------------------- *)
(* The Brouwer reduction theorem.                                            *)
(* ------------------------------------------------------------------------- *)


let BROUWER_REDUCTION_THEOREM_GEN = 
prove
 (`!P s:real^N->bool.
        (!f. (!n. closed(f n) /\ P(f n)) /\ (!n. f(SUC n) SUBSET f(n))
              ==> P(INTERS {f n | n IN (:num)})) /\
        closed s /\ P s
        ==> ?t. t SUBSET s /\ closed t /\ P t /\
                (!u. u SUBSET s /\ closed u /\ P u ==> ~(u PSUBSET t))`,

  REPEAT STRIP_TAC THEN
  SUBGOAL_THEN
   `?b:num->real^N->bool.
        (!m n. b m = b n <=> m = n) /\
        (!n. open (b n)) /\
        (!s. open s ==> (?k. s = UNIONS {b n | n IN k}))`
  STRIP_ASSUME_TAC THENL
   [REWRITE_TAC[UNIV_SECOND_COUNTABLE_SEQUENCE]; ALL_TAC] THEN
  X_CHOOSE_THEN `a:num->real^N->bool` MP_TAC
   (prove_recursive_functions_exist num_RECURSION
   `a 0 = (s:real^N->bool) /\
    (!n. a(SUC n) =
         if ?u. u SUBSET a(n) /\ closed u /\ P u /\ u INTER (b n) = {}
         then @u. u SUBSET a(n) /\ closed u /\ P u /\ u INTER (b n) = {}
         else a(n))`) THEN
  DISCH_THEN(CONJUNCTS_THEN2 (LABEL_TAC "base") (LABEL_TAC "step")) THEN
  EXISTS_TAC `INTERS {a n :real^N->bool | n IN (:num)}` THEN
  SUBGOAL_THEN `!n. (a:num->real^N->bool)(SUC n) SUBSET a(n)` ASSUME_TAC THENL
   [GEN_TAC THEN ASM_REWRITE_TAC[] THEN
    COND_CASES_TAC THEN REWRITE_TAC[SUBSET_REFL] THEN
    FIRST_X_ASSUM(MP_TAC o SELECT_RULE) THEN MESON_TAC[];
    ALL_TAC] THEN
  SUBGOAL_THEN `!n. (a:num->real^N->bool) n SUBSET s` ASSUME_TAC THENL
   [INDUCT_TAC THEN ASM_MESON_TAC[SUBSET_REFL; SUBSET_TRANS]; ALL_TAC] THEN
  SUBGOAL_THEN `!n. closed((a:num->real^N->bool) n) /\ P(a n)` ASSUME_TAC THENL
   [INDUCT_TAC THEN ASM_REWRITE_TAC[] THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
    FIRST_X_ASSUM(MP_TAC o SELECT_RULE) THEN MESON_TAC[];
    ALL_TAC] THEN
  REPEAT CONJ_TAC THENL
   [ASM SET_TAC[];
    MATCH_MP_TAC CLOSED_INTERS THEN
    ASM_REWRITE_TAC[FORALL_IN_GSPEC; IN_UNIV] THEN SET_TAC[];
    FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[];
    X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THEN
    REWRITE_TAC[PSUBSET_ALT] THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    REWRITE_TAC[INTERS_GSPEC; EXISTS_IN_GSPEC; IN_UNIV] THEN
    DISCH_THEN(X_CHOOSE_THEN `x:real^N` STRIP_ASSUME_TAC) THEN
    SUBGOAL_THEN
     `?n. x IN (b:num->real^N->bool)(n) /\ t INTER b n = {}`
    STRIP_ASSUME_TAC THENL
     [MP_TAC(ISPEC `(:real^N) DIFF t` OPEN_CONTAINS_BALL) THEN
      ASM_REWRITE_TAC[GSYM closed] THEN
      DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
      ASM_REWRITE_TAC[IN_DIFF; IN_UNIV; LEFT_IMP_EXISTS_THM] THEN
      REWRITE_TAC[SET_RULE `s SUBSET UNIV DIFF t <=> t INTER s = {}`] THEN
      X_GEN_TAC `e:real` THEN
      DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
      MP_TAC(ISPECL [`x:real^N`; `e:real`] CENTRE_IN_BALL) THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `ball(x:real^N,e)`) THEN
      ASM_REWRITE_TAC[OPEN_BALL; LEFT_IMP_EXISTS_THM] THEN
      X_GEN_TAC `k:num->bool` THEN DISCH_THEN SUBST1_TAC THEN
      REWRITE_TAC[IN_UNIONS; INTER_UNIONS; EMPTY_UNIONS; FORALL_IN_GSPEC] THEN
      SET_TAC[];
      REMOVE_THEN "step" (MP_TAC o SPEC `n:num`) THEN
      COND_CASES_TAC THENL
       [DISCH_THEN(ASSUME_TAC o SYM) THEN
        FIRST_X_ASSUM(MP_TAC o SELECT_RULE) THEN ASM_REWRITE_TAC[] THEN
        ASM SET_TAC[];
        FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [NOT_EXISTS_THM]) THEN
        DISCH_THEN(MP_TAC o SPEC `t:real^N->bool`) THEN ASM_REWRITE_TAC[] THEN
        ASM SET_TAC[]]]]);;


let BROUWER_REDUCTION_THEOREM = 
prove
 (`!P s:real^N->bool.
        (!f. (!n. compact(f n) /\ ~(f n = {}) /\ P(f n)) /\
             (!n. f(SUC n) SUBSET f(n))
             ==> P(INTERS {f n | n IN (:num)})) /\
        compact s /\ ~(s = {}) /\ P s
        ==> ?t. t SUBSET s /\ compact t /\ ~(t = {}) /\ P t /\
                (!u. u SUBSET s /\ closed u /\ ~(u = {}) /\ P u
                     ==> ~(u PSUBSET t))`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`\t:real^N->bool. ~(t = {}) /\ t SUBSET s /\ P t`;
                 `s:real^N->bool`]
        BROUWER_REDUCTION_THEOREM_GEN) THEN
  ASM_SIMP_TAC[COMPACT_IMP_CLOSED; SUBSET_REFL] THEN ANTS_TAC THENL
   [GEN_TAC THEN STRIP_TAC THEN
    SUBGOAL_THEN `!n. compact((f:num->real^N->bool) n)` ASSUME_TAC THENL
     [ASM_MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; BOUNDED_SUBSET]; ALL_TAC] THEN
    REPEAT CONJ_TAC THENL
     [MATCH_MP_TAC COMPACT_NEST THEN ASM_REWRITE_TAC[] THEN
      MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN ASM_SIMP_TAC[] THEN SET_TAC[];
      ASM SET_TAC[];
      FIRST_X_ASSUM MATCH_MP_TAC THEN ASM_REWRITE_TAC[]];
    MATCH_MP_TAC MONO_EXISTS THEN ASM_SIMP_TAC[] THEN
    ASM_MESON_TAC[COMPACT_EQ_BOUNDED_CLOSED; BOUNDED_SUBSET]]);;

(* ------------------------------------------------------------------------- *)
(* The Arzela-Ascoli theorem.                                                *)
(* ------------------------------------------------------------------------- *)


let SUBSEQUENCE_DIAGONALIZATION_LEMMA = 
prove
 (`!P:num->(num->A)->bool.
    (!i r:num->A. ?k. (!m n. m < n ==> k m < k n) /\ P i (r o k)) /\
    (!i r:num->A k1 k2 N.
        P i (r o k1) /\ (!j. N <= j ==> ?j'. j <= j' /\ k2 j = k1 j')
        ==> P i (r o k2))
    ==> !r:num->A. ?k. (!m n. m < n ==> k m < k n) /\ (!i. P i (r o k))`,

  REPEAT GEN_TAC THEN
  DISCH_THEN(CONJUNCTS_THEN2 MP_TAC STRIP_ASSUME_TAC) THEN
  GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV) [SKOLEM_THM] THEN
  REWRITE_TAC[FORALL_AND_THM; TAUT
   `(p ==> q /\ r) <=> (p ==> q) /\ (p ==> r)`] THEN
  DISCH_THEN(X_CHOOSE_THEN
   `kk:num->(num->A)->num->num` STRIP_ASSUME_TAC) THEN
  X_GEN_TAC `r:num->A` THEN
  (STRIP_ASSUME_TAC o prove_recursive_functions_exist num_RECURSION)
    `(rr 0 = (kk:num->(num->A)->num->num) 0 r) /\
     (!n. rr(SUC n) = rr n o kk (SUC n) (r o rr n))` THEN
  EXISTS_TAC `\n. (rr:num->num->num) n n` THEN REWRITE_TAC[ETA_AX] THEN
  SUBGOAL_THEN
   `(!i. (!m n. m < n ==> (rr:num->num->num) i m < rr i n)) /\
    (!i. (P:num->(num->A)->bool) i (r o rr i))`
  STRIP_ASSUME_TAC THENL
   [REWRITE_TAC[AND_FORALL_THM] THEN
    INDUCT_TAC THEN ASM_REWRITE_TAC[o_ASSOC] THEN
    REWRITE_TAC[o_THM] THEN ASM_MESON_TAC[];
    ALL_TAC] THEN
  SUBGOAL_THEN `!i j n. i <= j ==> (rr:num->num->num) i n <= rr j n`
  ASSUME_TAC THENL
   [REPEAT GEN_TAC THEN GEN_REWRITE_TAC LAND_CONV [LE_EXISTS] THEN
    SIMP_TAC[LEFT_IMP_EXISTS_THM] THEN SPEC_TAC(`j:num`,`j:num`) THEN
    ONCE_REWRITE_TAC[SWAP_FORALL_THM] THEN SIMP_TAC[FORALL_UNWIND_THM2] THEN
    INDUCT_TAC THEN REWRITE_TAC[ADD_CLAUSES; LE_REFL] THEN
    ASM_REWRITE_TAC[] THEN FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP
     (REWRITE_RULE[IMP_CONJ] LE_TRANS)) THEN REWRITE_TAC[o_THM] THEN
    FIRST_ASSUM(MATCH_MP_TAC o MATCH_MP
     (MESON[LE_LT]
       `!f:num->num.
        (!m n. m < n ==> f m < f n) ==> (!m n. m <= n ==> f m <= f n)`) o
       SPEC `i + d:num`) THEN
    SPEC_TAC(`n:num`,`n:num`) THEN MATCH_MP_TAC MONOTONE_BIGGER THEN
    ASM_SIMP_TAC[];
    ALL_TAC] THEN
  CONJ_TAC THENL
   [MAP_EVERY X_GEN_TAC [`m:num`; `n:num`] THEN DISCH_TAC THEN
    MATCH_MP_TAC LET_TRANS THEN
    EXISTS_TAC `(rr:num->num->num) n m` THEN
    ASM_MESON_TAC[LT_IMP_LE];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!m n i. n <= m ==> ?j. i <= j /\ (rr:num->num->num) m i = rr n j`
  ASSUME_TAC THENL
   [ALL_TAC;
    X_GEN_TAC `i:num` THEN FIRST_X_ASSUM MATCH_MP_TAC THEN
    EXISTS_TAC `(rr:num->num->num) i` THEN ASM_REWRITE_TAC[] THEN
    EXISTS_TAC `i:num` THEN ASM_MESON_TAC[]] THEN
  SUBGOAL_THEN
   `!p d i. ?j. i <= j /\ (rr:num->num->num) (p + d) i = rr p j`
   (fun th -> MESON_TAC[LE_EXISTS; th]) THEN
  X_GEN_TAC `p:num` THEN  MATCH_MP_TAC num_INDUCTION THEN
  ASM_REWRITE_TAC[ADD_CLAUSES] THEN CONJ_TAC THENL
   [MESON_TAC[LE_REFL]; ALL_TAC] THEN
  X_GEN_TAC `d:num` THEN DISCH_THEN(LABEL_TAC "+") THEN
  X_GEN_TAC `i:num` THEN ASM_REWRITE_TAC[o_THM] THEN
  REMOVE_THEN "+" (MP_TAC o SPEC
   `(kk:num->(num->A)->num->num) (SUC(p + d))
        ((r:num->A) o (rr:num->num->num) (p + d)) i`) THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `j:num` THEN
  MATCH_MP_TAC MONO_AND THEN REWRITE_TAC[] THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ] LE_TRANS) THEN
  SPEC_TAC(`i:num`,`i:num`) THEN MATCH_MP_TAC MONOTONE_BIGGER THEN
  ASM_REWRITE_TAC[o_THM] THEN ASM_MESON_TAC[]);;


let FUNCTION_CONVERGENT_SUBSEQUENCE = 
prove
 (`!f:num->real^M->real^N s M.
        COUNTABLE s /\ (!n x. x IN s ==> norm(f n x) <= M)
        ==> ?k. (!m n:num. m < n ==> k m < k n) /\
                !x. x IN s ==> ?l. ((\n. f (k n) x) --> l) sequentially`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^M->bool = {}` THENL
   [EXISTS_TAC `\n:num. n` THEN ASM_REWRITE_TAC[NOT_IN_EMPTY];
    ALL_TAC] THEN
  MP_TAC(ISPEC `s:real^M->bool` COUNTABLE_AS_IMAGE) THEN
  ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `X:num->real^M` THEN DISCH_THEN SUBST_ALL_TAC THEN
  MP_TAC(ISPEC
    `\i r. ?l. ((\n. ((f:num->real^M->real^N) o (r:num->num)) n
                     ((X:num->real^M) i)) --> l) sequentially`
   SUBSEQUENCE_DIAGONALIZATION_LEMMA) THEN
  REWRITE_TAC[FORALL_IN_IMAGE; o_THM; IN_UNIV] THEN
  ANTS_TAC THENL [ALL_TAC; DISCH_THEN MATCH_ACCEPT_TAC] THEN CONJ_TAC THENL
   [RULE_ASSUM_TAC(REWRITE_RULE[FORALL_IN_IMAGE; IN_UNIV]) THEN
    MAP_EVERY X_GEN_TAC [`i:num`; `r:num->num`] THEN
    MP_TAC(ISPEC `cball(vec 0:real^N,M)` compact) THEN
    REWRITE_TAC[COMPACT_CBALL] THEN DISCH_THEN(MP_TAC o SPEC
     `\n. (f:num->real^M->real^N) ((r:num->num) n) (X(i:num))`) THEN
    ASM_REWRITE_TAC[IN_CBALL_0; o_DEF] THEN MESON_TAC[];
    REPEAT GEN_TAC THEN REWRITE_TAC[LIM_SEQUENTIALLY; GE] THEN
    DISCH_THEN(CONJUNCTS_THEN2 MP_TAC ASSUME_TAC) THEN
    MATCH_MP_TAC MONO_EXISTS THEN GEN_TAC THEN
    MATCH_MP_TAC MONO_FORALL THEN GEN_TAC THEN
    MATCH_MP_TAC MONO_IMP THEN REWRITE_TAC[] THEN
    ASM_MESON_TAC[LE_TRANS; ARITH_RULE `MAX a b <= c <=> a <= c /\ b <= c`]]);;


let ARZELA_ASCOLI = 
prove
 (`!f:num->real^M->real^N s M.
        compact s /\
        (!n x. x IN s ==> norm(f n x) <= M) /\
        (!x e. x IN s /\ &0 < e
               ==> ?d. &0 < d /\
                       !n y. y IN s /\ norm(x - y) < d
                             ==> norm(f n x - f n y) < e)
        ==> ?g. g continuous_on s /\
                ?r. (!m n:num. m < n ==> r m < r n) /\
                    !e. &0 < e
                        ==> ?N. !n x. n >= N /\ x IN s
                                      ==> norm(f(r n) x - g x) < e`,

  REPEAT STRIP_TAC THEN REWRITE_TAC[GE] THEN
  MATCH_MP_TAC(MESON[]
   `(!k g. V k g ==> N g) /\ (?k. M k /\ ?g. V k g)
    ==> ?g. N g /\ ?k. M k /\ V k g`) THEN
  CONJ_TAC THENL
   [MAP_EVERY X_GEN_TAC [`k:num->num`; `g:real^M->real^N`] THEN
    STRIP_TAC THEN MATCH_MP_TAC(ISPEC `sequentially`
      CONTINUOUS_UNIFORM_LIMIT) THEN
    EXISTS_TAC `(f:num->real^M->real^N) o (k:num->num)` THEN
    ASM_SIMP_TAC[EVENTUALLY_SEQUENTIALLY; o_THM; TRIVIAL_LIMIT_SEQUENTIALLY;
                 RIGHT_IMP_FORALL_THM; IMP_IMP] THEN
    EXISTS_TAC `0` THEN REWRITE_TAC[continuous_on; dist] THEN
    ASM_MESON_TAC[NORM_SUB];
    ALL_TAC] THEN
  MP_TAC(ISPECL
   [`IMAGE (f:num->real^M->real^N) (:num)`;
    `s:real^M->bool`]
   COMPACT_UNIFORMLY_EQUICONTINUOUS) THEN
  REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM; FORALL_IN_IMAGE; IN_UNIV] THEN
  ANTS_TAC THENL
   [REWRITE_TAC[dist] THEN ONCE_REWRITE_TAC[NORM_SUB] THEN ASM_MESON_TAC[];
    ASM_REWRITE_TAC[] THEN FIRST_X_ASSUM(K ALL_TAC o SPEC `x:real^M`)] THEN
  REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN
  REWRITE_TAC[IMP_IMP; GSYM CONJ_ASSOC; dist] THEN
  DISCH_THEN(ASSUME_TAC o ONCE_REWRITE_RULE[NORM_SUB]) THEN
  REWRITE_TAC[GSYM dist; UNIFORMLY_CONVERGENT_EQ_CAUCHY] THEN
  X_CHOOSE_THEN `r:real^M->bool` STRIP_ASSUME_TAC
   (ISPEC `s:real^M->bool` SEPARABLE) THEN
  MP_TAC(ISPECL [`f:num->real^M->real^N`; `r:real^M->bool`; `M:real`]
        FUNCTION_CONVERGENT_SUBSEQUENCE) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `k:num->num` THEN
  REWRITE_TAC[CONVERGENT_EQ_CAUCHY; cauchy] THEN
  DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (LABEL_TAC "*")) THEN
  ASM_REWRITE_TAC[] THEN X_GEN_TAC `e:real` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(MP_TAC o SPEC `e / &3`) THEN
  ANTS_TAC THENL [ASM_REAL_ARITH_TAC; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
  FIRST_ASSUM(MP_TAC o GEN_REWRITE_RULE I [COMPACT_EQ_HEINE_BOREL]) THEN
  DISCH_THEN(MP_TAC o SPEC `IMAGE (\x:real^M. ball(x,d)) r`) THEN
  REWRITE_TAC[FORALL_IN_IMAGE; OPEN_BALL] THEN
  ONCE_REWRITE_TAC[TAUT `a /\ b /\ c <=> b /\ a /\ c`] THEN
  REWRITE_TAC[EXISTS_FINITE_SUBSET_IMAGE] THEN ANTS_TAC THENL
   [MATCH_MP_TAC SUBSET_TRANS THEN EXISTS_TAC `closure r:real^M->bool` THEN
    ASM_REWRITE_TAC[] THEN REWRITE_TAC[SUBSET; CLOSURE_APPROACHABLE] THEN
    X_GEN_TAC `x:real^M` THEN DISCH_THEN(MP_TAC o SPEC `d:real`) THEN
    ASM_REWRITE_TAC[UNIONS_IMAGE; IN_ELIM_THM; IN_BALL];
    DISCH_THEN(X_CHOOSE_THEN `t:real^M->bool` STRIP_ASSUME_TAC)] THEN
  REMOVE_THEN "*" MP_TAC THEN REWRITE_TAC[RIGHT_IMP_FORALL_THM] THEN
  GEN_REWRITE_TAC LAND_CONV [SWAP_FORALL_THM] THEN
  DISCH_THEN(MP_TAC o SPEC `e / &3`) THEN
  ASM_REWRITE_TAC[REAL_ARITH `&0 < e / &3 <=> &0 < e`] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `M:real^M->num` THEN DISCH_THEN(LABEL_TAC "*") THEN
  MP_TAC(ISPECL [`M:real^M->num`; `t:real^M->bool`]
    UPPER_BOUND_FINITE_SET) THEN
  ASM_REWRITE_TAC[] THEN MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `N:num` THEN
  DISCH_TAC THEN
  MAP_EVERY X_GEN_TAC [`m:num`; `n:num`; `x:real^M`] THEN STRIP_TAC THEN
  UNDISCH_TAC `s SUBSET UNIONS (IMAGE (\x:real^M. ball (x,d)) t)` THEN
  REWRITE_TAC[SUBSET; UNIONS_IMAGE; IN_ELIM_THM] THEN
  DISCH_THEN(MP_TAC o SPEC `x:real^M`) THEN
  ASM_REWRITE_TAC[IN_BALL; LEFT_IMP_EXISTS_THM; dist] THEN
  X_GEN_TAC `y:real^M` THEN STRIP_TAC THEN
  MATCH_MP_TAC(NORM_ARITH
   `norm(f (k(m:num)) y - f (k m) x) < e / &3 /\
    norm(f (k n) y - f (k n) x) < e / &3 /\
    norm(f (k m) y - f (k n) y) < e / &3
    ==> norm(f (k m) x - f (k n) x :real^M) < e`) THEN
  ASM_SIMP_TAC[] THEN REMOVE_THEN "*" (MP_TAC o SPEC `y:real^M`) THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  DISCH_THEN(MP_TAC o SPECL [`m:num`; `n:num`]) THEN
  ASM_REWRITE_TAC[dist; GE] THEN ASM_MESON_TAC[SUBSET; LE_TRANS]);;

(* ------------------------------------------------------------------------- *)
(* Two forms of the Baire propery of dense sets.                             *)
(* ------------------------------------------------------------------------- *)


let BAIRE = 
prove
 (`!g s:real^N->bool.
        closed s /\ COUNTABLE g /\
        (!t. t IN g
             ==> open_in (subtopology euclidean s) t /\ s SUBSET closure t)
        ==> s SUBSET closure(INTERS g)`,

  REPEAT STRIP_TAC THEN ASM_CASES_TAC `g:(real^N->bool)->bool = {}` THEN
  ASM_REWRITE_TAC[INTERS_0; CLOSURE_UNIV; SUBSET_UNIV] THEN
  MP_TAC(ISPEC `g:(real^N->bool)->bool` COUNTABLE_AS_IMAGE) THEN
  ASM_REWRITE_TAC[] THEN
  MAP_EVERY (C UNDISCH_THEN (K ALL_TAC))
   [`COUNTABLE(g:(real^N->bool)->bool)`;
    `~(g:(real^N->bool)->bool = {})`] THEN
  DISCH_THEN(X_CHOOSE_THEN `g:num->real^N->bool` SUBST_ALL_TAC) THEN
  RULE_ASSUM_TAC(REWRITE_RULE[FORALL_IN_IMAGE; IN_UNIV]) THEN
  REWRITE_TAC[SUBSET; CLOSURE_APPROACHABLE] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  X_GEN_TAC `e:real` THEN DISCH_TAC THEN ONCE_REWRITE_TAC[DIST_SYM] THEN
  REWRITE_TAC[GSYM IN_BALL; GSYM IN_INTER; MEMBER_NOT_EMPTY] THEN
  SUBGOAL_THEN
   `?t:num->real^N->bool.
        (!n. open_in (subtopology euclidean s) (t n) /\ ~(t n = {}) /\
             s INTER closure(t n) SUBSET g n /\
             closure(t n) SUBSET ball(x,e)) /\
        (!n. t(SUC n) SUBSET t n)`
  STRIP_ASSUME_TAC THENL
   [SUBGOAL_THEN
     `!u n. open_in (subtopology euclidean s) u /\ ~(u = {}) /\
            closure u SUBSET ball(x,e)
            ==> ?y. open_in (subtopology euclidean s) y /\
                    ~(y = {}) /\
                    s INTER closure y SUBSET (g:num->real^N->bool) n /\
                    closure y SUBSET ball(x,e) /\
                    y SUBSET u`
    ASSUME_TAC THENL
     [MAP_EVERY X_GEN_TAC [`u:real^N->bool`; `n:num`] THEN STRIP_TAC THEN
      SUBGOAL_THEN `?y:real^N. y IN u /\ y IN g(n:num)` STRIP_ASSUME_TAC THENL
       [FIRST_X_ASSUM(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC o SPEC `n:num`) THEN
        FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [GSYM MEMBER_NOT_EMPTY]) THEN
        FIRST_X_ASSUM(ASSUME_TAC o MATCH_MP OPEN_IN_IMP_SUBSET) THEN
        DISCH_THEN(X_CHOOSE_THEN `y:real^N` STRIP_ASSUME_TAC) THEN
        FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [open_in]) THEN
        DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (MP_TAC o SPEC `y:real^N`)) THEN
        ASM_REWRITE_TAC[LEFT_IMP_EXISTS_THM] THEN X_GEN_TAC `d:real` THEN
        STRIP_TAC THEN REWRITE_TAC[SUBSET; CLOSURE_APPROACHABLE] THEN
        ASM SET_TAC[];
        ALL_TAC] THEN
      SUBGOAL_THEN
       `open_in (subtopology euclidean s) (u INTER g(n:num):real^N->bool)`
      MP_TAC THENL [ASM_SIMP_TAC[OPEN_IN_INTER]; ALL_TAC] THEN
      GEN_REWRITE_TAC LAND_CONV [OPEN_IN_CONTAINS_BALL] THEN
      DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC (MP_TAC o SPEC `y:real^N`)) THEN
      ASM_REWRITE_TAC[IN_INTER] THEN
      DISCH_THEN(X_CHOOSE_THEN `d:real` STRIP_ASSUME_TAC) THEN
      EXISTS_TAC `s INTER ball(y:real^N,d / &2)` THEN
      SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_BALL] THEN REPEAT CONJ_TAC THENL
       [REWRITE_TAC[GSYM MEMBER_NOT_EMPTY] THEN EXISTS_TAC `y:real^N` THEN
        ASM_REWRITE_TAC[CENTRE_IN_BALL; REAL_HALF; IN_INTER] THEN
        ASM SET_TAC[];
        FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (SET_RULE
         `b SUBSET u INTER g ==> !s. s SUBSET b ==> s SUBSET g`)) THEN
        MATCH_MP_TAC(SET_RULE
         `closure(s INTER b) SUBSET closure b /\ closure b SUBSET c
          ==> s INTER closure(s INTER b) SUBSET c INTER s`) THEN
        SIMP_TAC[SUBSET_CLOSURE; INTER_SUBSET] THEN
        ASM_SIMP_TAC[CLOSURE_BALL; SUBSET_BALLS; REAL_HALF; DIST_REFL] THEN
        ASM_REAL_ARITH_TAC;
        FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (REWRITE_RULE[IMP_CONJ_ALT]
          SUBSET_TRANS)) THEN MATCH_MP_TAC SUBSET_CLOSURE;
        ALL_TAC] THEN
      FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP (SET_RULE
       `b INTER s SUBSET u INTER g ==> c SUBSET b
        ==> s INTER c SUBSET u`)) THEN
      REWRITE_TAC[SUBSET_BALLS; DIST_REFL] THEN ASM_REAL_ARITH_TAC;
      MATCH_MP_TAC DEPENDENT_CHOICE THEN ASM_SIMP_TAC[GSYM CONJ_ASSOC] THEN
      FIRST_X_ASSUM(MP_TAC o SPECL [`s INTER ball(x:real^N,e / &2)`; `0`]) THEN
      ASM_SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_BALL; GSYM MEMBER_NOT_EMPTY] THEN
      ANTS_TAC THENL [REWRITE_TAC[LEFT_AND_EXISTS_THM]; MESON_TAC[]] THEN
      EXISTS_TAC `x:real^N` THEN
      ASM_REWRITE_TAC[CENTRE_IN_BALL; REAL_HALF; IN_INTER] THEN
      TRANS_TAC SUBSET_TRANS `closure(ball(x:real^N,e / &2))` THEN
      SIMP_TAC[SUBSET_CLOSURE; INTER_SUBSET] THEN
      ASM_SIMP_TAC[CLOSURE_BALL; SUBSET_BALLS; REAL_HALF; DIST_REFL] THEN
      ASM_REAL_ARITH_TAC];
    MP_TAC(ISPEC
     `(\n. s INTER closure(t n)):num->real^N->bool` COMPACT_NEST) THEN
    ANTS_TAC THENL
     [REWRITE_TAC[FORALL_AND_THM] THEN REPEAT CONJ_TAC THENL
       [GEN_TAC THEN MATCH_MP_TAC CLOSED_INTER_COMPACT THEN
        ASM_MESON_TAC[BOUNDED_SUBSET; BOUNDED_BALL; COMPACT_EQ_BOUNDED_CLOSED;
                      CLOSED_CLOSURE];
        GEN_TAC THEN MATCH_MP_TAC(SET_RULE
         `~(t = {}) /\ t SUBSET s /\ t SUBSET closure t
          ==> ~(s INTER closure t = {})`) THEN
        ASM_MESON_TAC[CLOSURE_SUBSET; OPEN_IN_IMP_SUBSET];
        MATCH_MP_TAC TRANSITIVE_STEPWISE_LE THEN
        ASM_SIMP_TAC[SUBSET_CLOSURE; SET_RULE
         `t SUBSET u ==> s INTER t SUBSET s INTER u`] THEN
        SET_TAC[]];
      MATCH_MP_TAC(SET_RULE `s SUBSET t ==> ~(s = {}) ==> ~(t = {})`) THEN
      REWRITE_TAC[SUBSET_INTER] THEN
      REWRITE_TAC[SUBSET; IN_INTERS; FORALL_IN_IMAGE; FORALL_IN_GSPEC] THEN
      ASM SET_TAC[]]]);;


let BAIRE_ALT = 
prove
 (`!g s:real^N->bool.
        closed s /\ ~(s = {}) /\ COUNTABLE g /\ UNIONS g = s
        ==> ?t u. t IN g /\ open_in (subtopology euclidean s) u /\
                  u SUBSET (closure t)`,

  REPEAT STRIP_TAC THEN MP_TAC(ISPECL
  [`IMAGE (\t:real^N->bool. s DIFF closure t) g`; `s:real^N->bool`] BAIRE) THEN
  ASM_SIMP_TAC[COUNTABLE_IMAGE; FORALL_IN_IMAGE] THEN
  MATCH_MP_TAC(TAUT `~q /\ (~r ==> p) ==> (p ==> q) ==> r`) THEN
  CONJ_TAC THENL
   [MATCH_MP_TAC(SET_RULE
     `~(s = {}) /\ (t = {} ==> closure t = {}) /\ t = {}
      ==> ~(s SUBSET closure t)`) THEN
    ASM_SIMP_TAC[CLOSURE_EMPTY] THEN
    MATCH_MP_TAC(SET_RULE `i SUBSET s /\ s DIFF i = s ==> i = {}`) THEN
    CONJ_TAC THENL [REWRITE_TAC[INTERS_IMAGE] THEN ASM SET_TAC[]; ALL_TAC] THEN
    REWRITE_TAC[DIFF_INTERS] THEN
    REWRITE_TAC[SET_RULE `{f x | x IN IMAGE g s} = {f(g x) | x IN s}`] THEN
    REWRITE_TAC[SET_RULE `s DIFF (s DIFF t) = s INTER t`] THEN
    REWRITE_TAC[SET_RULE `{s INTER closure t | t IN g} =
                          {s INTER t | t IN IMAGE closure g}`] THEN
    SIMP_TAC[GSYM INTER_UNIONS; SET_RULE `s INTER t = s <=> s SUBSET t`] THEN
    FIRST_X_ASSUM(SUBST1_TAC o SYM) THEN
    GEN_REWRITE_TAC (LAND_CONV o RAND_CONV) [GSYM IMAGE_ID] THEN
    MATCH_MP_TAC UNIONS_MONO_IMAGE THEN REWRITE_TAC[CLOSURE_SUBSET];
    REWRITE_TAC[NOT_EXISTS_THM] THEN STRIP_TAC THEN
    X_GEN_TAC `t:real^N->bool` THEN REPEAT STRIP_TAC THENL
     [ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s DIFF (s INTER t)`] THEN
      MATCH_MP_TAC OPEN_IN_DIFF THEN
      ASM_SIMP_TAC[CLOSED_IN_CLOSED_INTER; CLOSED_CLOSURE; OPEN_IN_REFL];
      REWRITE_TAC[SUBSET] THEN X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
      REWRITE_TAC[CLOSURE_APPROACHABLE] THEN
      X_GEN_TAC `e:real` THEN DISCH_TAC THEN FIRST_X_ASSUM(MP_TAC o SPECL
       [`t:real^N->bool`; `s INTER ball(x:real^N,e)`]) THEN
      ASM_SIMP_TAC[OPEN_IN_OPEN_INTER; OPEN_BALL; SUBSET; IN_INTER; IN_BALL;
                   IN_DIFF] THEN
      MESON_TAC[DIST_SYM]]]);;

(* ------------------------------------------------------------------------- *)
(* Several variants of paracompactness.                                      *)
(* ------------------------------------------------------------------------- *)


let PARACOMPACT = 
prove
 (`!s c. (!t:real^N->bool. t IN c ==> open t) /\ s SUBSET UNIONS c
         ==> ?c'. s SUBSET UNIONS c' /\
                  (!u. u IN c'
                       ==> open u /\ ?t. t IN c /\ u SUBSET t) /\
                  (!x. x IN s
                       ==> ?v. open v /\ x IN v /\
                               FINITE {u | u IN c' /\ ~(u INTER v = {})})`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `s:real^N->bool = {}` THENL
   [EXISTS_TAC `{}:(real^N->bool)->bool` THEN
    ASM_REWRITE_TAC[EMPTY_SUBSET; NOT_IN_EMPTY];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!x:real^N. x IN s
               ==> ?t u. x IN u /\ open u /\ closure u SUBSET t /\ t IN c`
  MP_TAC THENL
   [X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N` o GEN_REWRITE_RULE I [SUBSET]) THEN
    ASM_REWRITE_TAC[IN_UNIONS] THEN MATCH_MP_TAC MONO_EXISTS THEN
    X_GEN_TAC `t:real^N->bool` THEN STRIP_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `t:real^N->bool`) THEN
    ASM_REWRITE_TAC[] THEN
    GEN_REWRITE_TAC LAND_CONV [OPEN_CONTAINS_CBALL] THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `e:real` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `ball(x:real^N,e)` THEN
    ASM_SIMP_TAC[OPEN_BALL; CENTRE_IN_BALL; CLOSURE_BALL];
    GEN_REWRITE_TAC (LAND_CONV o TOP_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
    REWRITE_TAC[LEFT_IMP_EXISTS_THM; SKOLEM_THM] THEN
    MAP_EVERY X_GEN_TAC
      [`f:real^N->real^N->bool`; `e:real^N->real^N->bool`] THEN
    STRIP_TAC] THEN
  MP_TAC(ISPEC `IMAGE (e:real^N->real^N->bool) s` LINDELOF) THEN
  ASM_SIMP_TAC[FORALL_IN_IMAGE] THEN
  ONCE_REWRITE_TAC[TAUT `p /\ q /\ r <=> q /\ p /\ r`] THEN
  REWRITE_TAC[EXISTS_COUNTABLE_SUBSET_IMAGE] THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real^N->bool`
    (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  ASM_CASES_TAC `k:real^N->bool = {}` THENL
   [ASM_REWRITE_TAC[] THEN ASM SET_TAC[]; ALL_TAC] THEN
  MP_TAC(ISPEC `k:real^N->bool` COUNTABLE_AS_IMAGE) THEN
  ASM_REWRITE_TAC[] THEN
  DISCH_THEN(X_CHOOSE_THEN `a:num->real^N` SUBST_ALL_TAC) THEN
  STRIP_TAC THEN EXISTS_TAC
  `{ f(a n:real^N) DIFF UNIONS {closure(e(a m)):real^N->bool | m < n} |
     n IN (:num)}` THEN
  REWRITE_TAC[FORALL_IN_GSPEC; IN_UNIV] THEN REPEAT CONJ_TAC THENL
   [X_GEN_TAC `n:num` THEN CONJ_TAC THENL
     [MATCH_MP_TAC OPEN_DIFF THEN
      CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      MATCH_MP_TAC CLOSED_UNIONS THEN
      REWRITE_TAC[FORALL_IN_GSPEC; CLOSED_CLOSURE] THEN
      ONCE_REWRITE_TAC[SIMPLE_IMAGE_GEN] THEN
      SIMP_TAC[FINITE_IMAGE; FINITE_NUMSEG_LT];
      EXISTS_TAC `f((a:num->real^N) n):real^N->bool` THEN ASM SET_TAC[]];
    REWRITE_TAC[SUBSET; UNIONS_GSPEC; IN_ELIM_THM; IN_DIFF] THEN
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    SUBGOAL_THEN `?n. x IN (f((a:num->real^N) n):real^N->bool)` MP_TAC THENL
     [RULE_ASSUM_TAC(REWRITE_RULE[UNIONS_IMAGE; EXISTS_IN_IMAGE]) THEN
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [EXTENSION]) THEN
      DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
      ASM_REWRITE_TAC[IN_ELIM_THM; IN_UNIV] THEN
      DISCH_THEN(MP_TAC o snd o EQ_IMP_RULE) THEN
      ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
      MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `n:num` THEN
      STRIP_TAC THEN
      FIRST_X_ASSUM(MP_TAC o SPEC `(a:num->real^N) n`) THEN
      ANTS_TAC THENL [ASM SET_TAC[]; ASM_MESON_TAC[CLOSURE_SUBSET; SUBSET]];
      GEN_REWRITE_TAC LAND_CONV [num_WOP] THEN
      MATCH_MP_TAC MONO_EXISTS THEN ASM SET_TAC[]];
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    RULE_ASSUM_TAC(REWRITE_RULE[UNIONS_IMAGE; EXISTS_IN_IMAGE]) THEN
    FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [EXTENSION]) THEN
    DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN
    ASM_REWRITE_TAC[IN_ELIM_THM; IN_UNIV] THEN
    DISCH_THEN(MP_TAC o snd o EQ_IMP_RULE) THEN
    ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    DISCH_THEN(X_CHOOSE_TAC `n:num`) THEN
    EXISTS_TAC `e((a:num->real^N) n):real^N->bool` THEN
    ASM_REWRITE_TAC[] THEN CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    REWRITE_TAC[SET_RULE
     `{u | (?n. u = f n) /\ P u} = IMAGE f {n |n| P(f n) /\ n IN (:num)}`] THEN
    MATCH_MP_TAC FINITE_IMAGE THEN MATCH_MP_TAC FINITE_SUBSET THEN
    EXISTS_TAC `{m:num | m <= n}` THEN REWRITE_TAC[FINITE_NUMSEG_LE] THEN
    REWRITE_TAC[SUBSET; IN_ELIM_THM; IN_UNIV] THEN
    X_GEN_TAC `m:num` THEN ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN
    REWRITE_TAC[NOT_LE] THEN DISCH_TAC THEN
    MATCH_MP_TAC(SET_RULE `u SUBSET t ==> (s DIFF t) INTER u = {}`) THEN
    REWRITE_TAC[SUBSET; IN_UNIONS; EXISTS_IN_GSPEC] THEN
    ASM_MESON_TAC[CLOSURE_SUBSET; SUBSET]]);;


let PARACOMPACT_CLOSED_IN = 
prove
 (`!u:real^N->bool s c.
        closed_in (subtopology euclidean u) s /\
        (!t:real^N->bool. t IN c ==> open_in (subtopology euclidean u) t) /\
        s SUBSET UNIONS c
         ==> ?c'. s SUBSET UNIONS c' /\
                  (!v. v IN c'
                       ==> open_in (subtopology euclidean u) v /\
                           ?t. t IN c /\ v SUBSET t) /\
                  (!x. x IN u
                       ==> ?v. open_in (subtopology euclidean u) v /\ x IN v /\
                               FINITE {n | n IN c' /\ ~(n INTER v = {})})`,

  REPEAT GEN_TAC THEN DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC
   (CONJUNCTS_THEN2 MP_TAC ASSUME_TAC)) THEN
  REWRITE_TAC[OPEN_IN_OPEN] THEN
  GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [RIGHT_IMP_EXISTS_THM] THEN
  REWRITE_TAC[SKOLEM_THM; LEFT_IMP_EXISTS_THM] THEN
  X_GEN_TAC `uu:(real^N->bool)->(real^N->bool)` THEN
  DISCH_THEN(ASSUME_TAC o GSYM) THEN
  FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [CLOSED_IN_CLOSED]) THEN
  DISCH_THEN(X_CHOOSE_THEN `k:real^N->bool`
   (CONJUNCTS_THEN2 ASSUME_TAC SUBST_ALL_TAC)) THEN
  MP_TAC(ISPECL
   [`u:real^N->bool`;
    `((:real^N) DIFF k) INSERT IMAGE (uu:(real^N->bool)->(real^N->bool)) c`]
   PARACOMPACT) THEN
  ASM_SIMP_TAC[FORALL_IN_IMAGE; UNIONS_IMAGE; UNIONS_INSERT; FORALL_IN_INSERT;
               EXISTS_IN_IMAGE; EXISTS_IN_INSERT; GSYM closed] THEN
  ANTS_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
  DISCH_THEN(X_CHOOSE_THEN `d:(real^N->bool)->bool` STRIP_ASSUME_TAC) THEN
  EXISTS_TAC `{u INTER v:real^N->bool | v IN d /\ ~(v INTER k = {})}` THEN
  REPEAT CONJ_TAC THENL
   [REWRITE_TAC[UNIONS_GSPEC] THEN ASM SET_TAC[];
    REWRITE_TAC[FORALL_IN_GSPEC] THEN ASM SET_TAC[];
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `v:real^N->bool` STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `u INTER v:real^N->bool` THEN ASM_REWRITE_TAC[IN_INTER] THEN
    CONJ_TAC THENL [ASM_MESON_TAC[]; ALL_TAC] THEN
    ONCE_REWRITE_TAC[SET_RULE
     `{y | y IN {f x | P x} /\ Q y} = IMAGE f {x | P x /\ Q(f x)}`] THEN
    MATCH_MP_TAC FINITE_IMAGE THEN
    FIRST_X_ASSUM(MATCH_MP_TAC o MATCH_MP
     (REWRITE_RULE[IMP_CONJ] FINITE_SUBSET)) THEN SET_TAC[]]);;


let PARACOMPACT_CLOSED = 
prove
 (`!s:real^N->bool c.
        closed s /\ (!t:real^N->bool. t IN c ==> open t) /\ s SUBSET UNIONS c
        ==> ?c'. s SUBSET UNIONS c' /\
                 (!u. u IN c' ==> open u /\ ?t. t IN c /\ u SUBSET t) /\
                 (!x. ?v. open v /\ x IN v /\
                          FINITE {u | u IN c' /\ ~(u INTER v = {})})`,

  REPEAT STRIP_TAC THEN
  MP_TAC(ISPECL [`(:real^N)`; `s:real^N->bool`; `c:(real^N->bool)->bool`]
        PARACOMPACT_CLOSED_IN) THEN
  ASM_REWRITE_TAC[SUBTOPOLOGY_UNIV; GSYM OPEN_IN; GSYM CLOSED_IN; IN_UNIV]);;

(* ------------------------------------------------------------------------- *)
(* Partitions of unity subordinate to locally finite open coverings.         *)
(* ------------------------------------------------------------------------- *)


let SUBORDINATE_PARTITION_OF_UNITY = 
prove
 (`!c s. s SUBSET UNIONS c /\ (!u. u IN c ==> open u) /\
         (!x. x IN s
              ==> ?v. open v /\ x IN v /\
                      FINITE {u | u IN c /\ ~(u INTER v = {})})
         ==> ?f:(real^N->bool)->real^N->real.
                      (!u. u IN c
                           ==> (lift o f u) continuous_on s /\
                               !x. x IN s ==> &0 <= f u x) /\
                      (!x u. u IN c /\ x IN s /\ ~(x IN u) ==> f u x = &0) /\
                      (!x. x IN s ==> sum c (\u. f u x) = &1) /\
                      (!x. x IN s
                           ==> ?n. open n /\ x IN n /\
                                   FINITE {u | u IN c /\
                                           ~(!x. x IN n ==> f u x = &0)})`,

  REPEAT STRIP_TAC THEN
  ASM_CASES_TAC `?u:real^N->bool. u IN c /\ s SUBSET u` THENL
   [FIRST_X_ASSUM(CHOOSE_THEN STRIP_ASSUME_TAC) THEN
    EXISTS_TAC `\v:real^N->bool x:real^N. if v = u then &1 else &0` THEN
    REWRITE_TAC[COND_RAND; COND_RATOR; o_DEF; REAL_POS;
                REAL_OF_NUM_EQ; ARITH_EQ;
                MESON[] `(if p then q else T) <=> p ==> q`] THEN
    ASM_SIMP_TAC[CONTINUOUS_ON_CONST; COND_ID; SUM_DELTA] THEN
    CONJ_TAC THENL [ASM SET_TAC[]; ALL_TAC] THEN
    X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    EXISTS_TAC `ball(x:real^N,&1)` THEN
    REWRITE_TAC[OPEN_BALL; CENTRE_IN_BALL; REAL_LT_01] THEN
    MATCH_MP_TAC FINITE_SUBSET THEN EXISTS_TAC `{u:real^N->bool}` THEN
    REWRITE_TAC[FINITE_SING; SUBSET; IN_ELIM_THM; IN_SING] THEN
    X_GEN_TAC `v:real^N->bool` THEN
    ASM_CASES_TAC `v:real^N->bool = u` THEN ASM_REWRITE_TAC[];
    ALL_TAC] THEN
  EXISTS_TAC `\u:real^N->bool x:real^N.
        if x IN s
        then setdist({x},s DIFF u) / sum c (\v. setdist({x},s DIFF v))
        else &0` THEN
  REWRITE_TAC[SUBSET; FORALL_IN_IMAGE] THEN
  SIMP_TAC[SUM_POS_LE; SETDIST_POS_LE; REAL_LE_DIV] THEN
  SIMP_TAC[SETDIST_SING_IN_SET; IN_DIFF; real_div; REAL_MUL_LZERO] THEN
  REWRITE_TAC[SUM_RMUL] THEN REWRITE_TAC[GSYM real_div] THEN
  MATCH_MP_TAC(TAUT `r /\ p /\ q ==> p /\ q /\ r`) THEN CONJ_TAC THENL
   [X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC MONO_EXISTS THEN X_GEN_TAC `n:real^N->bool` THEN
    REPEAT(DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
    ASM_REWRITE_TAC[] THEN
    MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] FINITE_SUBSET) THEN
    REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN X_GEN_TAC `u:real^N->bool` THEN
    ASM_CASES_TAC `(u:real^N->bool) IN c` THEN
    ASM_REWRITE_TAC[CONTRAPOS_THM] THEN DISCH_TAC THEN
    X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN
    REWRITE_TAC[real_div; REAL_ENTIRE] THEN
    COND_CASES_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_CASES_TAC `(y:real^N) IN u` THEN
    ASM_SIMP_TAC[SETDIST_SING_IN_SET; IN_DIFF; REAL_MUL_LZERO] THEN
    ASM SET_TAC[];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!v x:real^N. v IN c /\ x IN s /\ x IN v ==> &0 < setdist({x},s DIFF v)`
  ASSUME_TAC THENL
   [REPEAT STRIP_TAC THEN
    SIMP_TAC[SETDIST_POS_LE; REAL_ARITH `&0 < x <=> &0 <= x /\ ~(x = &0)`] THEN
    MP_TAC(ISPECL [`s:real^N->bool`; `s DIFF v:real^N->bool`; `x:real^N`]
        SETDIST_EQ_0_CLOSED_IN) THEN
    ONCE_REWRITE_TAC[SET_RULE `s DIFF t = s INTER (UNIV DIFF t)`] THEN
    ASM_SIMP_TAC[CLOSED_IN_CLOSED_INTER; GSYM OPEN_CLOSED] THEN
    DISCH_THEN SUBST1_TAC THEN ASM_REWRITE_TAC[] THEN
    ASM_REWRITE_TAC[IN_INTER; IN_DIFF; IN_UNION] THEN ASM SET_TAC[];
    ALL_TAC] THEN
  SUBGOAL_THEN
   `!x:real^N. x IN s ==> &0 < sum c (\v. setdist ({x},s DIFF v))`
  ASSUME_TAC THENL
   [X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
    ONCE_REWRITE_TAC[GSYM SUM_SUPPORT] THEN
    REWRITE_TAC[support; NEUTRAL_REAL_ADD] THEN
    MATCH_MP_TAC SUM_POS_LT THEN REWRITE_TAC[SETDIST_POS_LE] THEN
    CONJ_TAC THENL
     [FIRST_X_ASSUM(MP_TAC o SPEC `x:real^N`) THEN ASM_REWRITE_TAC[] THEN
      DISCH_THEN(CHOOSE_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
      DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
      MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] FINITE_SUBSET) THEN
      REWRITE_TAC[SUBSET; IN_ELIM_THM] THEN X_GEN_TAC `u:real^N->bool` THEN
      ASM_CASES_TAC `(x:real^N) IN u` THEN
      ASM_SIMP_TAC[SETDIST_SING_IN_SET; IN_DIFF] THEN ASM SET_TAC[];
      FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [SUBSET]) THEN
      DISCH_THEN(MP_TAC o SPEC `x:real^N`) THEN REWRITE_TAC[IN_UNIONS] THEN
      ASM_REWRITE_TAC[IN_ELIM_THM] THEN MATCH_MP_TAC MONO_EXISTS THEN
      ASM_MESON_TAC[REAL_LT_IMP_NZ]];
    ALL_TAC] THEN
  ASM_SIMP_TAC[REAL_LT_IMP_NZ; REAL_DIV_REFL; o_DEF] THEN
  X_GEN_TAC `u:real^N->bool` THEN DISCH_TAC THEN
  MATCH_MP_TAC CONTINUOUS_ON_EQ THEN
  EXISTS_TAC `\x:real^N.
        lift(setdist({x},s DIFF u) / sum c (\v. setdist({x},s DIFF v)))` THEN
  SIMP_TAC[] THEN REWRITE_TAC[real_div; LIFT_CMUL] THEN
  MATCH_MP_TAC CONTINUOUS_ON_MUL THEN
  SIMP_TAC[CONTINUOUS_ON_LIFT_SETDIST; o_DEF] THEN
  MATCH_MP_TAC(REWRITE_RULE[o_DEF] CONTINUOUS_ON_INV) THEN
  ASM_SIMP_TAC[REAL_LT_IMP_NZ; CONTINUOUS_ON_EQ_CONTINUOUS_WITHIN] THEN
  X_GEN_TAC `x:real^N` THEN DISCH_TAC THEN
  FIRST_X_ASSUM(fun th ->
    MP_TAC(SPEC `x:real^N` th) THEN ASM_REWRITE_TAC[] THEN
    DISCH_THEN(X_CHOOSE_THEN `n:real^N->bool` STRIP_ASSUME_TAC)) THEN
  MATCH_MP_TAC CONTINUOUS_TRANSFORM_WITHIN_OPEN_IN THEN
  MAP_EVERY EXISTS_TAC
   [`\x:real^N. lift(sum {v | v IN c /\ ~(v INTER n = {})}
                         (\v. setdist({x},s DIFF v)))`;
    `s INTER n:real^N->bool`] THEN
  ASM_SIMP_TAC[IN_INTER; OPEN_IN_OPEN_INTER] THEN CONJ_TAC THENL
   [X_GEN_TAC `y:real^N` THEN DISCH_TAC THEN AP_TERM_TAC THEN
    CONV_TAC SYM_CONV THEN MATCH_MP_TAC SUM_EQ_SUPERSET THEN
    ASM_REWRITE_TAC[SUBSET_RESTRICT] THEN X_GEN_TAC `v:real^N->bool` THEN
    DISCH_THEN(CONJUNCTS_THEN2 ASSUME_TAC MP_TAC) THEN
    ASM_REWRITE_TAC[IN_ELIM_THM] THEN DISCH_TAC THEN
    MATCH_MP_TAC SETDIST_SING_IN_SET THEN ASM SET_TAC[];
    ASM_SIMP_TAC[LIFT_SUM; o_DEF] THEN MATCH_MP_TAC CONTINUOUS_VSUM THEN
    ASM_SIMP_TAC[CONTINUOUS_AT_LIFT_SETDIST; CONTINUOUS_AT_WITHIN]]);;