1 let assign = new_definition
2 `Assign (f:S->S) (q:S->bool) = q o f`;;
4 parse_as_infix(";;",(18,"right"));;
6 let sequence = new_definition
7 `(c1:(S->bool)->(S->bool)) ;; (c2:(S->bool)->(S->bool)) = c1 o c2`;;
9 let if_def = new_definition
10 `If e (c:(S->bool)->(S->bool)) q = {s | if e s then c q s else q s}`;;
12 let ite_def = new_definition
13 `Ite e (c1:(S->bool)->(S->bool)) c2 q =
14 {s | if e s then c1 q s else c2 q s}`;;
16 let while_RULES,while_INDUCT,while_CASES = new_inductive_definition
17 `!q s. If e (c ;; while e c) q s ==> while e c q s`;;
19 let while_def = new_definition
21 {s | !w. (!s:S. (if e(s) then c w s else q s) ==> w s) ==> w s}`;;
23 let monotonic = new_definition
24 `monotonic c <=> !q q'. q SUBSET q' ==> (c q) SUBSET (c q')`;;
26 let MONOTONIC_ASSIGN = prove
27 (`monotonic (Assign f)`,
28 SIMP_TAC[monotonic; assign; SUBSET; o_THM; IN]);;
30 let MONOTONIC_IF = prove
31 (`monotonic c ==> monotonic (If e c)`,
32 REWRITE_TAC[monotonic; if_def] THEN SET_TAC[]);;
34 let MONOTONIC_ITE = prove
35 (`monotonic c1 /\ monotonic c2 ==> monotonic (Ite e c1 c2)`,
36 REWRITE_TAC[monotonic; ite_def] THEN SET_TAC[]);;
38 let MONOTONIC_SEQ = prove
39 (`monotonic c1 /\ monotonic c2 ==> monotonic (c1 ;; c2)`,
40 REWRITE_TAC[monotonic; sequence; o_THM] THEN SET_TAC[]);;
42 let MONOTONIC_WHILE = prove
43 (`monotonic c ==> monotonic(While e c)`,
44 REWRITE_TAC[monotonic; while_def] THEN SET_TAC[]);;
49 ==> (!s. If e (c ;; While e c) q s ==> While e c q s) /\
50 (!w'. (!s. If e (c ;; (\q. w')) q s ==> w' s)
51 ==> (!a. While e c q a ==> w' a)) /\
52 (!s. While e c q s <=> If e (c ;; While e c) q s)`,
53 REPEAT GEN_TAC THEN DISCH_TAC THEN
54 (MP_TAC o GEN_ALL o DISCH_ALL o derive_nonschematic_inductive_relations)
55 `!s:S. (if e s then c w s else q s) ==> w s` THEN
56 REWRITE_TAC[if_def; sequence; o_THM; IN_ELIM_THM; IMP_IMP] THEN
57 DISCH_THEN MATCH_MP_TAC THEN
58 REWRITE_TAC[FUN_EQ_THM; while_def; IN_ELIM_THM] THEN
59 POP_ASSUM MP_TAC THEN REWRITE_TAC[monotonic] THEN SET_TAC[]);;
62 (`!e c. monotonic c ==> (While e c = If e (c ;; While e c))`,
63 REWRITE_TAC[FUN_EQ_THM] THEN MESON_TAC[WHILE_THM]);;
65 let correct = new_definition
66 `correct p c q <=> p SUBSET (c q)`;;
68 let CORRECT_PRESTRENGTH = prove
69 (`!p p' c q. p SUBSET p' /\ correct p' c q ==> correct p c q`,
70 REWRITE_TAC[correct; SUBSET_TRANS]);;
72 let CORRECT_POSTWEAK = prove
73 (`!p c q q'. monotonic c /\ correct p c q' /\ q' SUBSET q ==> correct p c q`,
74 REWRITE_TAC[correct; monotonic] THEN SET_TAC[]);;
76 let CORRECT_ASSIGN = prove
77 (`!p f q. (p SUBSET (q o f)) ==> correct p (Assign f) q`,
78 REWRITE_TAC[correct; assign]);;
80 let CORRECT_SEQ = prove
82 monotonic c1 /\ correct p c1 r /\ correct r c2 q
83 ==> correct p (c1 ;; c2) q`,
84 REWRITE_TAC[correct; sequence; monotonic; o_THM] THEN SET_TAC[]);;
86 let CORRECT_ITE = prove
88 correct (p INTER e) c1 q /\ correct (p INTER (UNIV DIFF e)) c2 q
89 ==> correct p (Ite e c1 c2) q`,
90 REWRITE_TAC[correct; ite_def] THEN SET_TAC[]);;
92 let CORRECT_IF = prove
94 correct (p INTER e) c q /\ p INTER (UNIV DIFF e) SUBSET q
95 ==> correct p (If e c) q`,
96 REWRITE_TAC[correct; if_def] THEN SET_TAC[]);;
98 let CORRECT_WHILE = prove
99 (`!(<<) p c q e invariant.
102 p SUBSET invariant /\
103 (UNIV DIFF e) INTER invariant SUBSET q /\
104 (!X:S. correct (invariant INTER e INTER (\s. X = s)) c
105 (invariant INTER (\s. s << X)))
106 ==> correct p (While e c) q`,
107 REWRITE_TAC[correct; SUBSET; IN_INTER; IN_UNIV; IN_DIFF; IN] THEN
108 REPEAT GEN_TAC THEN STRIP_TAC THEN
109 SUBGOAL_THEN `!s:S. invariant s ==> While e c q s` MP_TAC THENL
110 [ALL_TAC; ASM_MESON_TAC[]] THEN
111 FIRST_ASSUM(MATCH_MP_TAC o REWRITE_RULE[WF_IND]) THEN
112 X_GEN_TAC `s:S` THEN REPEAT DISCH_TAC THEN
113 FIRST_ASSUM(fun th -> ONCE_REWRITE_TAC[MATCH_MP WHILE_FIX th]) THEN
114 REWRITE_TAC[if_def; sequence; o_THM; IN_ELIM_THM] THEN
115 COND_CASES_TAC THENL [ALL_TAC; ASM_MESON_TAC[]] THEN
116 FIRST_X_ASSUM(MP_TAC o SPECL [`s:S`; `s:S`]) THEN ASM_REWRITE_TAC[] THEN
117 FIRST_X_ASSUM(MP_TAC o GEN_REWRITE_RULE I [monotonic]) THEN
118 REWRITE_TAC[SUBSET; IN; RIGHT_IMP_FORALL_THM] THEN
119 DISCH_THEN MATCH_MP_TAC THEN ASM_SIMP_TAC[INTER; IN_ELIM_THM; IN]);;
121 let assert_def = new_definition
122 `assert (p:S->bool) (q:S->bool) = q`;;
124 let variant_def = new_definition
125 `variant ((<<):S->S->bool) (q:S->bool) = q`;;
127 let CORRECT_SEQ_VC = prove
129 monotonic c1 /\ correct p c1 r /\ correct r c2 q
130 ==> correct p (c1 ;; assert r ;; c2) q`,
131 REWRITE_TAC[correct; sequence; monotonic; assert_def; o_THM] THEN SET_TAC[]);;
133 let CORRECT_WHILE_VC = prove
134 (`!(<<) p c q e invariant.
137 p SUBSET invariant /\
138 (UNIV DIFF e) INTER invariant SUBSET q /\
139 (!X:S. correct (invariant INTER e INTER (\s. X = s)) c
140 (invariant INTER (\s. s << X)))
141 ==> correct p (While e (assert invariant ;; variant(<<) ;; c)) q`,
142 REPEAT STRIP_TAC THEN
143 REWRITE_TAC[sequence; variant_def; assert_def; o_DEF; ETA_AX] THEN
144 ASM_MESON_TAC[CORRECT_WHILE]);;
146 let MONOTONIC_ASSERT = prove
147 (`monotonic (assert p)`,
148 REWRITE_TAC[assert_def; monotonic]);;
150 let MONOTONIC_VARIANT = prove
151 (`monotonic (variant p)`,
152 REWRITE_TAC[variant_def; monotonic]);;
155 REPEAT(MATCH_MP_TAC MONOTONIC_WHILE ORELSE
156 (MAP_FIRST MATCH_MP_TAC
157 [MONOTONIC_SEQ; MONOTONIC_IF; MONOTONIC_ITE] THEN CONJ_TAC)) THEN
158 MAP_FIRST MATCH_ACCEPT_TAC
159 [MONOTONIC_ASSIGN; MONOTONIC_ASSERT; MONOTONIC_VARIANT];;
163 [MATCH_MP_TAC CORRECT_SEQ_VC THEN CONJ_TAC THENL [MONO_TAC; CONJ_TAC];
164 MATCH_MP_TAC CORRECT_ITE THEN CONJ_TAC;
165 MATCH_MP_TAC CORRECT_IF THEN CONJ_TAC;
166 MATCH_MP_TAC CORRECT_WHILE_VC THEN REPEAT CONJ_TAC THENL
167 [MONO_TAC; TRY(MATCH_ACCEPT_TAC WF_MEASURE); ALL_TAC; ALL_TAC;
168 REWRITE_TAC[FORALL_PAIR_THM; MEASURE] THEN REPEAT GEN_TAC];
169 MATCH_MP_TAC CORRECT_ASSIGN];;
171 needs "Library/prime.ml";;
173 (* ------------------------------------------------------------------------- *)
175 (* while (!(x == 0 || y == 0)) *)
176 (* { if (x < y) y = y - x; *)
177 (* else x = x - y; *)
179 (* if (x == 0) x = y; *)
180 (* ------------------------------------------------------------------------- *)
184 (Assign (\(m,n,x,y). m,n,m,n) ;; // x,y := m,n
185 assert (\(m,n,x,y). x = m /\ y = n) ;;
186 While (\(m,n,x,y). ~(x = 0 \/ y = 0))
187 (assert (\(m,n,x,y). gcd(x,y) = gcd(m,n)) ;;
188 variant(MEASURE(\(m,n,x,y). x + y)) ;;
189 Ite (\(m,n,x,y). x < y)
190 (Assign (\(m,n,x,y). m,n,x,y - x))
191 (Assign (\(m,n,x,y). m,n,x - y,y))) ;;
192 assert (\(m,n,x,y). (x = 0 \/ y = 0) /\ gcd(x,y) = gcd(m,n)) ;;
193 If (\(m,n,x,y). x = 0) (Assign (\(m,n,x,y). (m,n,y,y))))
194 (\(m,n,x,y). gcd(m,n) = x)`;;
199 e(REPEAT VC_TAC THEN REWRITE_TAC[SUBSET; FORALL_PAIR_THM] THEN
200 MAP_EVERY X_GEN_TAC [`m:num`; `n:num`; `x:num`; `y:num`] THEN
201 REWRITE_TAC[IN; INTER; UNIV; DIFF; o_DEF; IN_ELIM_THM; PAIR_EQ] THEN
202 CONV_TAC(TOP_DEPTH_CONV GEN_BETA_CONV) THEN SIMP_TAC[]);;
204 e(SIMP_TAC[GCD_SUB; LT_IMP_LE]);;
207 e(SIMP_TAC[GCD_SUB; NOT_LT] THEN ARITH_TAC);;
209 e(MESON_TAC[GCD_0]);;
211 e(MESON_TAC[GCD_0; GCD_SYM]);;
213 parse_as_infix("refines",(12,"right"));;
215 let refines = new_definition
216 `c2 refines c1 <=> !q. c1(q) SUBSET c2(q)`;;
218 let REFINES_REFL = prove
220 REWRITE_TAC[refines; SUBSET_REFL]);;
222 let REFINES_TRANS = prove
223 (`!c1 c2 c3. c3 refines c2 /\ c2 refines c1 ==> c3 refines c1`,
224 REWRITE_TAC[refines] THEN MESON_TAC[SUBSET_TRANS]);;
226 let REFINES_CORRECT = prove
227 (`correct p c1 q /\ c2 refines c1 ==> correct p c2 q`,
228 REWRITE_TAC[correct; refines] THEN MESON_TAC[SUBSET_TRANS]);;
230 let REFINES_WHILE = prove
231 (`c' refines c ==> While e c' refines While e c`,
232 REWRITE_TAC[refines; while_def; SUBSET; IN_ELIM_THM; IN] THEN MESON_TAC[]);;
234 let specification = new_definition
235 `specification(p,q) r = if q SUBSET r then p else {}`;;
237 let REFINES_SPECIFICATION = prove
238 (`c refines specification(p,q) ==> correct p c q`,
239 REWRITE_TAC[specification; correct; refines] THEN
240 MESON_TAC[SUBSET_REFL; SUBSET_EMPTY]);;