1 (* ========================================================================= *)
2 (* Generic Grobner basis algorithm. *)
4 (* Whatever the instantiation, it basically solves the universal theory of *)
5 (* the complex numbers, or equivalently something like the theory of all *)
6 (* commutative cancellation semirings with no nilpotent elements and having *)
7 (* characteristic zero. We could do "all rings" by a more elaborate integer *)
8 (* version of Grobner bases, but I don't have any useful applications. *)
10 (* (c) Copyright, John Harrison 1998-2007 *)
11 (* ========================================================================= *)
13 needs "normalizer.ml";;
15 (* ------------------------------------------------------------------------- *)
16 (* Type for recording history, i.e. how a polynomial was obtained. *)
17 (* ------------------------------------------------------------------------- *)
21 | Mmul of (num * (int list)) * history
22 | Add of history * history;;
24 (* ------------------------------------------------------------------------- *)
25 (* Overall function; everything else is local. *)
26 (* ------------------------------------------------------------------------- *)
28 let RING_AND_IDEAL_CONV =
30 (* ----------------------------------------------------------------------- *)
31 (* Monomial ordering. *)
32 (* ----------------------------------------------------------------------- *)
35 let rec lexorder l1 l2 =
38 | (x1::o1,x2::o2) -> x1 > x2 or x1 = x2 & lexorder o1 o2
39 | _ -> failwith "morder: inconsistent monomial lengths" in
40 fun m1 m2 -> let n1 = itlist (+) m1 0
41 and n2 = itlist (+) m2 0 in
42 n1 < n2 or n1 = n2 & lexorder m1 m2 in
44 (* ----------------------------------------------------------------------- *)
45 (* Arithmetic on canonical polynomials. *)
46 (* ----------------------------------------------------------------------- *)
48 let grob_neg = map (fun (c,m) -> (minus_num c,m)) in
50 let rec grob_add l1 l2 =
54 | ((c1,m1)::o1,(c2,m2)::o2) ->
56 let c = c1+/c2 and rest = grob_add o1 o2 in
57 if c =/ num_0 then rest else (c,m1)::rest
58 else if morder_lt m2 m1 then (c1,m1)::(grob_add o1 l2)
59 else (c2,m2)::(grob_add l1 o2) in
61 let grob_sub l1 l2 = grob_add l1 (grob_neg l2) in
63 let grob_mmul (c1,m1) (c2,m2) = (c1*/c2,map2 (+) m1 m2) in
65 let rec grob_cmul cm pol = map (grob_mmul cm) pol in
67 let rec grob_mul l1 l2 =
70 | (h1::t1) -> grob_add (grob_cmul h1 l2) (grob_mul t1 l2) in
74 [c,vs] when forall (fun x -> x = 0) vs ->
75 if c =/ num_0 then failwith "grob_inv: division by zero"
77 | _ -> failwith "grob_inv: non-constant divisor polynomial" in
81 [c,l] when forall (fun x -> x = 0) l ->
82 if c =/ num_0 then failwith "grob_div: division by zero"
83 else grob_cmul (num_1 // c,l) l1
84 | _ -> failwith "grob_div: non-constant divisor polynomial" in
86 let rec grob_pow vars l n =
87 if n < 0 then failwith "grob_pow: negative power"
88 else if n = 0 then [num_1,map (fun v -> 0) vars]
89 else grob_mul l (grob_pow vars l (n - 1)) in
91 (* ----------------------------------------------------------------------- *)
92 (* Monomial division operation. *)
93 (* ----------------------------------------------------------------------- *)
95 let mdiv (c1,m1) (c2,m2) =
97 map2 (fun n1 n2 -> if n1 < n2 then failwith "mdiv" else n1-n2) m1 m2) in
99 (* ----------------------------------------------------------------------- *)
100 (* Lowest common multiple of two monomials. *)
101 (* ----------------------------------------------------------------------- *)
103 let mlcm (c1,m1) (c2,m2) = (num_1,map2 max m1 m2) in
105 (* ----------------------------------------------------------------------- *)
106 (* Reduce monomial cm by polynomial pol, returning replacement for cm. *)
107 (* ----------------------------------------------------------------------- *)
109 let reduce1 cm (pol,hpol) =
111 [] -> failwith "reduce1"
112 | cm1::cms -> try let (c,m) = mdiv cm cm1 in
113 (grob_cmul (minus_num c,m) cms,
114 Mmul((minus_num c,m),hpol))
115 with Failure _ -> failwith "reduce1" in
117 (* ----------------------------------------------------------------------- *)
118 (* Try this for all polynomials in a basis. *)
119 (* ----------------------------------------------------------------------- *)
121 let reduceb cm basis = tryfind (fun p -> reduce1 cm p) basis in
123 (* ----------------------------------------------------------------------- *)
124 (* Reduction of a polynomial (always picking largest monomial possible). *)
125 (* ----------------------------------------------------------------------- *)
127 let rec reduce basis (pol,hist) =
130 | cm::ptl -> try let q,hnew = reduceb cm basis in
131 reduce basis (grob_add q ptl,Add(hnew,hist))
133 let q,hist' = reduce basis (ptl,hist) in
136 (* ----------------------------------------------------------------------- *)
137 (* Check for orthogonality w.r.t. LCM. *)
138 (* ----------------------------------------------------------------------- *)
140 let orthogonal l p1 p2 =
141 snd l = snd(grob_mmul (hd p1) (hd p2)) in
143 (* ----------------------------------------------------------------------- *)
144 (* Compute S-polynomial of two polynomials. *)
145 (* ----------------------------------------------------------------------- *)
147 let spoly cm ph1 ph2 =
151 | (cm1::ptl1,his1),(cm2::ptl2,his2) ->
152 (grob_sub (grob_cmul (mdiv cm cm1) ptl1)
153 (grob_cmul (mdiv cm cm2) ptl2),
154 Add(Mmul(mdiv cm cm1,his1),
155 Mmul(mdiv (minus_num(fst cm),snd cm) cm2,his2))) in
157 (* ----------------------------------------------------------------------- *)
158 (* Make a polynomial monic. *)
159 (* ----------------------------------------------------------------------- *)
161 let monic (pol,hist) =
162 if pol = [] then (pol,hist) else
163 let c',m' = hd pol in
164 (map (fun (c,m) -> (c//c',m)) pol,
165 Mmul((num_1 // c',map (K 0) m'),hist)) in
167 (* ----------------------------------------------------------------------- *)
168 (* The most popular heuristic is to order critical pairs by LCM monomial. *)
169 (* ----------------------------------------------------------------------- *)
171 let forder ((c1,m1),_) ((c2,m2),_) = morder_lt m1 m2 in
173 (* ----------------------------------------------------------------------- *)
174 (* Stupid stuff forced on us by lack of equality test on num type. *)
175 (* ----------------------------------------------------------------------- *)
177 let rec poly_lt p q =
181 | (c1,m1)::o1,(c2,m2)::o2 ->
183 c1 =/ c2 & (m1 < m2 or m1 = m2 & poly_lt o1 o2) in
185 let align ((p,hp),(q,hq)) =
186 if poly_lt p q then ((p,hp),(q,hq)) else ((q,hq),(p,hp)) in
189 forall2 (fun (c1,m1) (c2,m2) -> c1 =/ c2 & m1 = m2) p1 p2 in
191 let memx ((p1,h1),(p2,h2)) ppairs =
192 not (exists (fun ((q1,_),(q2,_)) -> poly_eq p1 q1 & poly_eq p2 q2)
195 (* ----------------------------------------------------------------------- *)
196 (* Buchberger's second criterion. *)
197 (* ----------------------------------------------------------------------- *)
199 let criterion2 basis (lcm,((p1,h1),(p2,h2))) opairs =
200 exists (fun g -> not(poly_eq (fst g) p1) & not(poly_eq (fst g) p2) &
201 can (mdiv lcm) (hd(fst g)) &
202 not(memx (align(g,(p1,h1))) (map snd opairs)) &
203 not(memx (align(g,(p2,h2))) (map snd opairs))) basis in
205 (* ----------------------------------------------------------------------- *)
206 (* Test for hitting constant polynomial. *)
207 (* ----------------------------------------------------------------------- *)
209 let constant_poly p =
210 length p = 1 & forall ((=) 0) (snd(hd p)) in
212 (* ----------------------------------------------------------------------- *)
213 (* Grobner basis algorithm. *)
214 (* ----------------------------------------------------------------------- *)
216 let rec grobner_basis basis pairs =
217 Format.print_string(string_of_int(length basis)^" basis elements and "^
218 string_of_int(length pairs)^" critical pairs");
219 Format.print_newline();
222 | (l,(p1,p2))::opairs ->
223 let (sp,hist as sph) = monic (reduce basis (spoly l p1 p2)) in
224 if sp = [] or criterion2 basis (l,(p1,p2)) opairs
225 then grobner_basis basis opairs else
226 if constant_poly sp then grobner_basis (sph::basis) [] else
228 map (fun p -> mlcm (hd(fst p)) (hd sp),align(p,sph)) basis in
230 (fun (l,(p,q)) -> not(orthogonal l (fst p) (fst q))) rawcps in
231 grobner_basis (sph::basis)
232 (merge forder opairs (mergesort forder newcps)) in
234 (* ----------------------------------------------------------------------- *)
235 (* Interreduce initial polynomials. *)
236 (* ----------------------------------------------------------------------- *)
238 let rec grobner_interreduce rpols ipols =
240 [] -> map monic (rev rpols)
241 | p::ps -> let p' = reduce (rpols @ ps) p in
242 if fst p' = [] then grobner_interreduce rpols ps
243 else grobner_interreduce (p'::rpols) ps in
245 (* ----------------------------------------------------------------------- *)
246 (* Overall function. *)
247 (* ----------------------------------------------------------------------- *)
250 let npols = map2 (fun p n -> p,Start n) pols (0--(length pols - 1)) in
251 let phists = filter (fun (p,_) -> p <> []) npols in
252 let bas = grobner_interreduce [] (map monic phists) in
253 let prs0 = allpairs (fun x y -> x,y) bas bas in
254 let prs1 = filter (fun ((x,_),(y,_)) -> poly_lt x y) prs0 in
255 let prs2 = map (fun (p,q) -> mlcm (hd(fst p)) (hd(fst q)),(p,q)) prs1 in
257 filter (fun (l,(p,q)) -> not(orthogonal l (fst p) (fst q))) prs2 in
258 grobner_basis bas (mergesort forder prs3) in
260 (* ----------------------------------------------------------------------- *)
261 (* Get proof of contradiction from Grobner basis. *)
262 (* ----------------------------------------------------------------------- *)
264 let grobner_refute pols =
265 let gb = grobner pols in
266 snd(find (fun (p,h) -> length p = 1 & forall ((=)0) (snd(hd p))) gb) in
268 (* ----------------------------------------------------------------------- *)
269 (* Turn proof into a certificate as sum of multipliers. *)
271 (* In principle this is very inefficient: in a heavily shared proof it may *)
272 (* make the same calculation many times. Could add a cache or something. *)
273 (* ----------------------------------------------------------------------- *)
275 let rec resolve_proof vars prf =
278 | Start m -> [m,[num_1,map (K 0) vars]]
280 let lis = resolve_proof vars lin in
281 map (fun (n,p) -> n,grob_cmul pol p) lis
283 let lis1 = resolve_proof vars lin1
284 and lis2 = resolve_proof vars lin2 in
285 let dom = setify(union (map fst lis1) (map fst lis2)) in
286 map (fun n -> let a = try assoc n lis1 with Failure _ -> []
287 and b = try assoc n lis2 with Failure _ -> [] in
288 n,grob_add a b) dom in
290 (* ----------------------------------------------------------------------- *)
291 (* Run the procedure and produce Weak Nullstellensatz certificate. *)
292 (* ----------------------------------------------------------------------- *)
294 let grobner_weak vars pols =
295 let cert = resolve_proof vars (grobner_refute pols) in
297 itlist (itlist (lcm_num o denominator o fst) o snd) cert (num_1) in
298 l,map (fun (i,p) -> i,map (fun (d,m) -> (l*/d,m)) p) cert in
300 (* ----------------------------------------------------------------------- *)
301 (* Prove polynomial is in ideal generated by others, using Grobner basis. *)
302 (* ----------------------------------------------------------------------- *)
304 let grobner_ideal vars pols pol =
305 let pol',h = reduce (grobner pols) (grob_neg pol,Start(-1)) in
306 if pol' <> [] then failwith "grobner_ideal: not in the ideal" else
307 resolve_proof vars h in
309 (* ----------------------------------------------------------------------- *)
310 (* Produce Strong Nullstellensatz certificate for a power of pol. *)
311 (* ----------------------------------------------------------------------- *)
313 let grobner_strong vars pols pol =
314 if pol = [] then 1,num_1,[] else
315 let vars' = (concl TRUTH)::vars in
316 let grob_z = [num_1,1::(map (fun x -> 0) vars)]
317 and grob_1 = [num_1,(map (fun x -> 0) vars')]
318 and augment = map (fun (c,m) -> (c,0::m)) in
319 let pols' = map augment pols
320 and pol' = augment pol in
321 let allpols = (grob_sub (grob_mul grob_z pol') grob_1)::pols' in
322 let l,cert = grobner_weak vars' allpols in
323 let d = itlist (itlist (max o hd o snd) o snd) cert 0 in
324 let transform_monomial (c,m) =
325 grob_cmul (c,tl m) (grob_pow vars pol (d - hd m)) in
326 let transform_polynomial q = itlist (grob_add o transform_monomial) q [] in
327 let cert' = map (fun (c,q) -> c-1,transform_polynomial q)
328 (filter (fun (k,_) -> k <> 0) cert) in
331 (* ----------------------------------------------------------------------- *)
332 (* Overall parametrized universal procedure for (semi)rings. *)
333 (* We return an IDEAL_CONV and the actual ring prover. *)
334 (* ----------------------------------------------------------------------- *)
337 (`!(add:A->A->A) (mul:A->A->A) (n0:A).
338 (!x. mul n0 x = n0) /\
339 (!x y z. (add x y = add x z) <=> (y = z)) /\
340 (!w x y z. (add (mul w y) (mul x z) = add (mul w z) (mul x y)) <=>
342 ==> (!a b c d. ~(a = b) /\ ~(c = d) <=>
343 ~(add (mul a c) (mul b d) =
344 add (mul a d) (mul b c))) /\
345 (!n a b c d. ~(n = n0)
346 ==> (a = b) /\ ~(c = d)
347 ==> ~(add a (mul n c) = add b (mul n d)))`,
348 REPEAT GEN_TAC THEN STRIP_TAC THEN
349 ASM_REWRITE_TAC[GSYM DE_MORGAN_THM] THEN
350 REPEAT GEN_TAC THEN DISCH_TAC THEN STRIP_TAC THEN
351 FIRST_X_ASSUM(MP_TAC o SPECL [`n0:A`; `n:A`; `d:A`; `c:A`]) THEN
352 ONCE_REWRITE_TAC[GSYM CONTRAPOS_THM] THEN ASM_SIMP_TAC[])
353 and FINAL_RULE = MATCH_MP(TAUT `(p ==> F) ==> (~q = p) ==> q`)
354 and false_tm = `F` in
355 let rec refute_disj rfn tm =
357 Comb(Comb(Const("\\/",_),l),r) ->
358 DISJ_CASES (ASSUME tm) (refute_disj rfn l) (refute_disj rfn r)
360 fun (ring_dest_const,ring_mk_const,RING_EQ_CONV,
361 ring_neg_tm,ring_add_tm,ring_sub_tm,
362 ring_inv_tm,ring_mul_tm,ring_div_tm,ring_pow_tm,
363 RING_INTEGRAL,RABINOWITSCH_THM,RING_NORMALIZE_CONV) ->
365 TOP_DEPTH_CONV BETA_CONV THENC
367 CONDS_ELIM_CONV THENC
369 (if is_iff(snd(strip_forall(concl RABINOWITSCH_THM)))
370 then GEN_REWRITE_CONV ONCE_DEPTH_CONV [RABINOWITSCH_THM]
372 GEN_REWRITE_CONV REDEPTH_CONV
375 RIGHT_AND_FORALL_THM;
382 RIGHT_AND_EXISTS_THM] in
383 let ring_dest_neg t =
384 let l,r = dest_comb t in
385 if l = ring_neg_tm then r else failwith "ring_dest_neg"
386 and ring_dest_inv t =
387 let l,r = dest_comb t in
388 if l = ring_inv_tm then r else failwith "ring_dest_inv"
389 and ring_dest_add = dest_binop ring_add_tm
390 and ring_mk_add = mk_binop ring_add_tm
391 and ring_dest_sub = dest_binop ring_sub_tm
392 and ring_dest_mul = dest_binop ring_mul_tm
393 and ring_mk_mul = mk_binop ring_mul_tm
394 and ring_dest_div = dest_binop ring_div_tm
395 and ring_dest_pow = dest_binop ring_pow_tm
396 and ring_mk_pow = mk_binop ring_pow_tm in
397 let rec grobvars tm acc =
398 if can ring_dest_const tm then acc
399 else if can ring_dest_neg tm then grobvars (rand tm) acc
400 else if can ring_dest_pow tm & is_numeral (rand tm)
401 then grobvars (lhand tm) acc
402 else if can ring_dest_add tm or can ring_dest_sub tm
403 or can ring_dest_mul tm
404 then grobvars (lhand tm) (grobvars (rand tm) acc)
405 else if can ring_dest_inv tm then
406 let gvs = grobvars (rand tm) [] in
407 if gvs = [] then acc else tm::acc
408 else if can ring_dest_div tm then
409 let lvs = grobvars (lhand tm) acc
410 and gvs = grobvars (rand tm) [] in
411 if gvs = [] then lvs else tm::acc
413 let rec grobify_term vars tm =
414 try if not(mem tm vars) then failwith "" else
415 [num_1,map (fun i -> if i = tm then 1 else 0) vars]
416 with Failure _ -> try
417 let x = ring_dest_const tm in
418 if x =/ num_0 then [] else [x,map (fun v -> 0) vars]
419 with Failure _ -> try
420 grob_neg(grobify_term vars (ring_dest_neg tm))
421 with Failure _ -> try
422 grob_inv(grobify_term vars (ring_dest_inv tm))
423 with Failure _ -> try
424 let l,r = ring_dest_add tm in
425 grob_add (grobify_term vars l) (grobify_term vars r)
426 with Failure _ -> try
427 let l,r = ring_dest_sub tm in
428 grob_sub (grobify_term vars l) (grobify_term vars r)
429 with Failure _ -> try
430 let l,r = ring_dest_mul tm in
431 grob_mul (grobify_term vars l) (grobify_term vars r)
432 with Failure _ -> try
433 let l,r = ring_dest_div tm in
434 grob_div (grobify_term vars l) (grobify_term vars r)
435 with Failure _ -> try
436 let l,r = ring_dest_pow tm in
437 grob_pow vars (grobify_term vars l) (dest_small_numeral r)
439 failwith "grobify_term: unknown or invalid term" in
440 let grobify_equation vars tm =
441 let l,r = dest_eq tm in
442 grob_sub (grobify_term vars l) (grobify_term vars r) in
443 let grobify_equations tm =
444 let cjs = conjuncts tm in
446 itlist (fun eq a -> grobvars (lhand eq) (grobvars (rand eq) a))
448 let vars = sort (fun x y -> x < y) (setify rawvars) in
449 vars,map (grobify_equation vars) cjs in
450 let holify_polynomial =
451 let holify_varpow (v,n) =
452 if n = 1 then v else ring_mk_pow v (mk_small_numeral n) in
453 let holify_monomial vars (c,m) =
454 let xps = map holify_varpow
455 (filter (fun (_,n) -> n <> 0) (zip vars m)) in
456 end_itlist ring_mk_mul (ring_mk_const c :: xps) in
457 let holify_polynomial vars p =
458 if p = [] then ring_mk_const (num_0)
459 else end_itlist ring_mk_add (map (holify_monomial vars) p) in
461 let (pth_idom,pth_ine) = CONJ_PAIR(MATCH_MP pth_step RING_INTEGRAL) in
462 let IDOM_RULE = CONV_RULE(REWR_CONV pth_idom) in
463 let PROVE_NZ n = EQF_ELIM(RING_EQ_CONV
464 (mk_eq(ring_mk_const n,ring_mk_const(num_0)))) in
465 let NOT_EQ_01 = PROVE_NZ (num_1)
466 and INE_RULE n = MATCH_MP(MATCH_MP pth_ine (PROVE_NZ n))
467 and MK_ADD th1 th2 = MK_COMB(AP_TERM ring_add_tm th1,th2) in
468 let execute_proof vars eths prf =
469 let x,th1 = SPEC_VAR(CONJUNCT1(CONJUNCT2 RING_INTEGRAL)) in
470 let y,th2 = SPEC_VAR th1 in
471 let z,th3 = SPEC_VAR th2 in
472 let SUB_EQ_RULE = GEN_REWRITE_RULE I
473 [SYM(INST [mk_comb(ring_neg_tm,z),x] th3)] in
474 let initpols = map (CONV_RULE(BINOP_CONV RING_NORMALIZE_CONV) o
476 let ADD_RULE th1 th2 =
477 CONV_RULE (BINOP_CONV RING_NORMALIZE_CONV)
478 (MK_COMB(AP_TERM ring_add_tm th1,th2))
479 and MUL_RULE vars m th =
480 CONV_RULE (BINOP_CONV RING_NORMALIZE_CONV)
481 (AP_TERM (mk_comb(ring_mul_tm,holify_polynomial vars [m]))
483 let execache = ref [] in
484 let memoize prf x = (execache := (prf,x)::(!execache)); x in
485 let rec assoceq a l =
487 [] -> failwith "assoceq"
488 | (x,y)::t -> if x==a then y else assoceq a t in
489 let rec run_proof vars prf =
490 try assoceq prf (!execache) with Failure _ ->
492 Start m -> el m initpols
494 memoize prf (ADD_RULE (run_proof vars p1) (run_proof vars p2))
496 memoize prf (MUL_RULE vars m (run_proof vars p2))) in
497 let th = run_proof vars prf in
498 execache := []; CONV_RULE RING_EQ_CONV th in
500 if tm = false_tm then ASSUME tm else
501 let nths0,eths0 = partition (is_neg o concl) (CONJUNCTS(ASSUME tm)) in
502 let nths = filter (is_eq o rand o concl) nths0
503 and eths = filter (is_eq o concl) eths0 in
505 let th1 = end_itlist (fun th1 th2 -> IDOM_RULE(CONJ th1 th2)) nths in
506 let th2 = CONV_RULE(RAND_CONV(BINOP_CONV RING_NORMALIZE_CONV)) th1 in
507 let l,r = dest_eq(rand(concl th2)) in
508 EQ_MP (EQF_INTRO th2) (REFL l)
509 else if nths = [] & not(is_var ring_neg_tm) then
510 let vars,pols = grobify_equations(list_mk_conj(map concl eths)) in
511 execute_proof vars eths (grobner_refute pols)
513 let vars,l,cert,noteqth =
515 let vars,pols = grobify_equations(list_mk_conj(map concl eths)) in
516 let l,cert = grobner_weak vars pols in
517 vars,l,cert,NOT_EQ_01
520 (fun th1 th2 -> IDOM_RULE(CONJ th1 th2)) nths in
522 grobify_equations(list_mk_conj(rand(concl nth)::map concl eths)) in
523 let deg,l,cert = grobner_strong vars pols pol in
525 CONV_RULE(RAND_CONV(BINOP_CONV RING_NORMALIZE_CONV)) nth in
526 let th2 = funpow deg (IDOM_RULE o CONJ th1) NOT_EQ_01 in
528 Format.print_string("Translating certificate to HOL inferences");
529 Format.print_newline();
531 (fun (i,p) -> i,filter (fun (c,m) -> c >/ num_0) p) cert
533 (fun (i,p) -> i,map (fun (c,m) -> minus_num c,m)
534 (filter (fun (c,m) -> c </ num_0) p)) cert in
536 map (fun (i,p) -> i,holify_polynomial vars p) cert_pos
538 map (fun (i,p) -> i,holify_polynomial vars p) cert_neg in
540 if pols = [] then REFL(ring_mk_const num_0) else
542 (map (fun (i,p) -> AP_TERM(mk_comb(ring_mul_tm,p)) (el i eths))
544 let th1 = thm_fn herts_pos and th2 = thm_fn herts_neg in
545 let th3 = CONJ(MK_ADD (SYM th1) th2) noteqth in
546 let th4 = CONV_RULE (RAND_CONV(BINOP_CONV RING_NORMALIZE_CONV))
548 let l,r = dest_eq(rand(concl th4)) in
549 EQ_MP (EQF_INTRO th4) (REFL l) in
551 let avs = frees tm in
552 let tm' = list_mk_forall(avs,tm) in
553 let th1 = INITIAL_CONV(mk_neg tm') in
554 let evs,bod = strip_exists(rand(concl th1)) in
555 if is_forall bod then failwith "RING: non-universal formula" else
556 let th1a = WEAK_DNF_CONV bod in
557 let boda = rand(concl th1a) in
558 let th2a = refute_disj REFUTE boda in
559 let th2b = TRANS th1a (EQF_INTRO(NOT_INTRO(DISCH boda th2a))) in
560 let th2 = UNDISCH(NOT_ELIM(EQF_ELIM th2b)) in
561 let th3 = itlist SIMPLE_CHOOSE evs th2 in
562 SPECL avs (MATCH_MP (FINAL_RULE (DISCH_ALL th3)) th1)
564 let rawvars = itlist grobvars (tm::tms) [] in
565 let vars = sort (fun x y -> x < y) (setify rawvars) in
566 let pols = map (grobify_term vars) tms and pol = grobify_term vars tm in
567 let cert = grobner_ideal vars pols pol in
568 map (fun n -> let p = assocd n cert [] in holify_polynomial vars p)
569 (0--(length pols-1)) in
572 (* ----------------------------------------------------------------------- *)
573 (* Separate out the cases. *)
574 (* ----------------------------------------------------------------------- *)
576 let RING parms = fst(RING_AND_IDEAL_CONV parms);;
578 let ideal_cofactors parms = snd(RING_AND_IDEAL_CONV parms);;
580 (* ------------------------------------------------------------------------- *)
581 (* Simplify a natural number assertion to eliminate conditionals, DIV, MOD, *)
582 (* PRE, cutoff subtraction, EVEN and ODD. Try to do it in a way that makes *)
583 (* new quantifiers universal. At the moment we don't split "<=>" which would *)
584 (* make this quantifier selection work there too; better to do NNF first if *)
585 (* you care. This also applies to EVEN and ODD. *)
586 (* ------------------------------------------------------------------------- *)
588 let NUM_SIMPLIFY_CONV =
590 and div_tm = `(DIV):num->num->num`
591 and mod_tm = `(MOD):num->num->num`
592 and p_tm = `P:num->bool` and n_tm = `n:num` and m_tm = `m:num`
593 and q_tm = `P:num->num->bool` and a_tm = `a:num` and b_tm = `b:num` in
594 let is_pre tm = is_comb tm & rator tm = pre_tm
595 and is_sub = is_binop `(-):num->num->num`
597 let is_div = is_binop div_tm and is_mod = is_binop mod_tm in
598 fun tm -> is_div tm or is_mod tm
599 and contains_quantifier =
600 can (find_term (fun t -> is_forall t or is_exists t or is_uexists t))
601 and BETA2_CONV = RATOR_CONV BETA_CONV THENC BETA_CONV
602 and PRE_ELIM_THM'' = CONV_RULE (RAND_CONV NNF_CONV) PRE_ELIM_THM
603 and SUB_ELIM_THM'' = CONV_RULE (RAND_CONV NNF_CONV) SUB_ELIM_THM
604 and DIVMOD_ELIM_THM'' = CONV_RULE (RAND_CONV NNF_CONV) DIVMOD_ELIM_THM
605 and pth_evenodd = prove
606 (`(EVEN(x) <=> (!y. ~(x = SUC(2 * y)))) /\
607 (ODD(x) <=> (!y. ~(x = 2 * y))) /\
608 (~EVEN(x) <=> (!y. ~(x = 2 * y))) /\
609 (~ODD(x) <=> (!y. ~(x = SUC(2 * y))))`,
610 REWRITE_TAC[GSYM NOT_EXISTS_THM; GSYM EVEN_EXISTS; GSYM ODD_EXISTS] THEN
611 REWRITE_TAC[NOT_EVEN; NOT_ODD]) in
612 let rec NUM_MULTIPLY_CONV pos tm =
613 if is_forall tm or is_exists tm or is_uexists tm then
614 BINDER_CONV (NUM_MULTIPLY_CONV pos) tm
615 else if is_imp tm & contains_quantifier tm then
616 COMB2_CONV (RAND_CONV(NUM_MULTIPLY_CONV(not pos)))
617 (NUM_MULTIPLY_CONV pos) tm
618 else if (is_conj tm or is_disj tm or is_iff tm) &
619 contains_quantifier tm
620 then BINOP_CONV (NUM_MULTIPLY_CONV pos) tm
621 else if is_neg tm & not pos & contains_quantifier tm then
622 RAND_CONV (NUM_MULTIPLY_CONV (not pos)) tm
624 try let t = find_term (fun t -> is_pre t & free_in t tm) tm in
625 let ty = type_of t in
627 let p = mk_abs(v,subst [v,t] tm) in
628 let th0 = if pos then PRE_ELIM_THM'' else PRE_ELIM_THM' in
629 let th1 = INST [p,p_tm; rand t,n_tm] th0 in
630 let th2 = CONV_RULE(COMB2_CONV (RAND_CONV BETA_CONV)
631 (BINDER_CONV(RAND_CONV BETA_CONV))) th1 in
632 CONV_RULE(RAND_CONV (NUM_MULTIPLY_CONV pos)) th2
633 with Failure _ -> try
634 let t = find_term (fun t -> is_sub t & free_in t tm) tm in
635 let ty = type_of t in
637 let p = mk_abs(v,subst [v,t] tm) in
638 let th0 = if pos then SUB_ELIM_THM'' else SUB_ELIM_THM' in
639 let th1 = INST [p,p_tm; lhand t,a_tm; rand t,b_tm] th0 in
640 let th2 = CONV_RULE(COMB2_CONV (RAND_CONV BETA_CONV)
641 (BINDER_CONV(RAND_CONV BETA_CONV))) th1 in
642 CONV_RULE(RAND_CONV (NUM_MULTIPLY_CONV pos)) th2
643 with Failure _ -> try
644 let t = find_term (fun t -> is_divmod t & free_in t tm) tm in
645 let x = lhand t and y = rand t in
646 let dtm = mk_comb(mk_comb(div_tm,x),y)
647 and mtm = mk_comb(mk_comb(mod_tm,x),y) in
648 let vd = genvar(type_of dtm)
649 and vm = genvar(type_of mtm) in
650 let p = list_mk_abs([vd;vm],subst[vd,dtm; vm,mtm] tm) in
651 let th0 = if pos then DIVMOD_ELIM_THM'' else DIVMOD_ELIM_THM' in
652 let th1 = INST [p,q_tm; x,m_tm; y,n_tm] th0 in
653 let th2 = CONV_RULE(COMB2_CONV(RAND_CONV BETA2_CONV)
654 (funpow 2 BINDER_CONV(RAND_CONV BETA2_CONV))) th1 in
655 CONV_RULE(RAND_CONV (NUM_MULTIPLY_CONV pos)) th2
656 with Failure _ -> REFL tm in
657 NUM_REDUCE_CONV THENC
658 CONDS_CELIM_CONV THENC
660 NUM_MULTIPLY_CONV true THENC
661 NUM_REDUCE_CONV THENC
662 GEN_REWRITE_CONV ONCE_DEPTH_CONV [pth_evenodd];;
664 (* ----------------------------------------------------------------------- *)
665 (* Natural number version of ring procedure with this normalization. *)
666 (* ----------------------------------------------------------------------- *)
669 let NUM_INTEGRAL_LEMMA = prove
670 (`(w = x + d) /\ (y = z + e)
671 ==> ((w * y + x * z = w * z + x * y) <=> (w = x) \/ (y = z))`,
672 DISCH_THEN(fun th -> REWRITE_TAC[th]) THEN
673 REWRITE_TAC[LEFT_ADD_DISTRIB; RIGHT_ADD_DISTRIB; GSYM ADD_ASSOC] THEN
674 ONCE_REWRITE_TAC[AC ADD_AC
675 `a + b + c + d + e = a + c + e + b + d`] THEN
676 REWRITE_TAC[EQ_ADD_LCANCEL; EQ_ADD_LCANCEL_0; MULT_EQ_0]) in
677 let NUM_INTEGRAL = prove
679 (!x y z. (x + y = x + z) <=> (y = z)) /\
680 (!w x y z. (w * y + x * z = w * z + x * y) <=> (w = x) \/ (y = z))`,
681 REWRITE_TAC[MULT_CLAUSES; EQ_ADD_LCANCEL] THEN
683 DISJ_CASES_TAC (SPECL [`w:num`; `x:num`] LE_CASES) THEN
684 DISJ_CASES_TAC (SPECL [`y:num`; `z:num`] LE_CASES) THEN
686 (CHOOSE_THEN SUBST1_TAC o REWRITE_RULE[LE_EXISTS])) THEN
687 ASM_MESON_TAC[NUM_INTEGRAL_LEMMA; ADD_SYM; MULT_SYM]) in
689 RING(dest_numeral,mk_numeral,NUM_EQ_CONV,
690 genvar bool_ty,`(+):num->num->num`,genvar bool_ty,
691 genvar bool_ty,`(*):num->num->num`,genvar bool_ty,
692 `(EXP):num->num->num`,
693 NUM_INTEGRAL,TRUTH,NUM_NORMALIZE_CONV) in
694 let initconv = NUM_SIMPLIFY_CONV THENC GEN_REWRITE_CONV DEPTH_CONV [ADD1]
696 fun tm -> let th = initconv tm in
697 if rand(concl th) = t_tm then th
698 else EQ_MP (SYM th) (rawring(rand(concl th)));;