src/HOL/IMP/VC.thy
author wenzelm
Thu Dec 08 20:15:50 2005 +0100 (2005-12-08)
changeset 18372 2bffdf62fe7f
parent 16417 9bc16273c2d4
child 20503 503ac4c5ef91
permissions -rw-r--r--
tuned proofs;
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(*  Title:      HOL/IMP/VC.thy
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    ID:         $Id$
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    Author:     Tobias Nipkow
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    Copyright   1996 TUM
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acom: annotated commands
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vc:   verification-conditions
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awp:   weakest (liberal) precondition
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*)
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header "Verification Conditions"
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theory VC imports Hoare begin
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datatype  acom = Askip
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               | Aass   loc aexp
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               | Asemi  acom acom
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               | Aif    bexp acom acom
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               | Awhile bexp assn acom
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consts
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  vc :: "acom => assn => assn"
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  awp :: "acom => assn => assn"
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  vcawp :: "acom => assn => assn \<times> assn"
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  astrip :: "acom => com"
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primrec
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  "awp Askip Q = Q"
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  "awp (Aass x a) Q = (\<lambda>s. Q(s[x\<mapsto>a s]))"
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  "awp (Asemi c d) Q = awp c (awp d Q)"
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  "awp (Aif b c d) Q = (\<lambda>s. (b s-->awp c Q s) & (~b s-->awp d Q s))"
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  "awp (Awhile b I c) Q = I"
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primrec
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  "vc Askip Q = (\<lambda>s. True)"
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  "vc (Aass x a) Q = (\<lambda>s. True)"
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  "vc (Asemi c d) Q = (\<lambda>s. vc c (awp d Q) s & vc d Q s)"
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  "vc (Aif b c d) Q = (\<lambda>s. vc c Q s & vc d Q s)"
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  "vc (Awhile b I c) Q = (\<lambda>s. (I s & ~b s --> Q s) &
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                              (I s & b s --> awp c I s) & vc c I s)"
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primrec
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  "astrip Askip = SKIP"
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  "astrip (Aass x a) = (x:==a)"
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  "astrip (Asemi c d) = (astrip c;astrip d)"
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  "astrip (Aif b c d) = (\<IF> b \<THEN> astrip c \<ELSE> astrip d)"
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  "astrip (Awhile b I c) = (\<WHILE> b \<DO> astrip c)"
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(* simultaneous computation of vc and awp: *)
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primrec
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  "vcawp Askip Q = (\<lambda>s. True, Q)"
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  "vcawp (Aass x a) Q = (\<lambda>s. True, \<lambda>s. Q(s[x\<mapsto>a s]))"
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  "vcawp (Asemi c d) Q = (let (vcd,wpd) = vcawp d Q;
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                              (vcc,wpc) = vcawp c wpd
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                          in (\<lambda>s. vcc s & vcd s, wpc))"
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  "vcawp (Aif b c d) Q = (let (vcd,wpd) = vcawp d Q;
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                              (vcc,wpc) = vcawp c Q
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                          in (\<lambda>s. vcc s & vcd s,
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                              \<lambda>s.(b s --> wpc s) & (~b s --> wpd s)))"
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  "vcawp (Awhile b I c) Q = (let (vcc,wpc) = vcawp c I
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                             in (\<lambda>s. (I s & ~b s --> Q s) &
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                                     (I s & b s --> wpc s) & vcc s, I))"
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(*
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Soundness and completeness of vc
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*)
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declare hoare.intros [intro]
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lemma l: "!s. P s --> P s" by fast
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lemma vc_sound: "(!s. vc c Q s) --> |- {awp c Q} astrip c {Q}"
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apply (induct c fixing: Q)
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    apply (simp_all (no_asm))
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    apply fast
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   apply fast
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  apply fast
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 (* if *)
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 apply atomize
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 apply (tactic "Deepen_tac 4 1")
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(* while *)
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apply atomize
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apply (intro allI impI)
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apply (rule conseq)
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  apply (rule l)
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 apply (rule While)
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 defer
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 apply fast
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apply (rule_tac P="awp c fun2" in conseq)
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  apply fast
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 apply fast
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apply fast
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done
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lemma awp_mono [rule_format (no_asm)]:
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  "!P Q. (!s. P s --> Q s) --> (!s. awp c P s --> awp c Q s)"
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apply (induct c)
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    apply (simp_all (no_asm_simp))
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apply (rule allI, rule allI, rule impI)
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apply (erule allE, erule allE, erule mp)
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apply (erule allE, erule allE, erule mp, assumption)
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done
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lemma vc_mono [rule_format (no_asm)]:
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  "!P Q. (!s. P s --> Q s) --> (!s. vc c P s --> vc c Q s)"
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apply (induct c)
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    apply (simp_all (no_asm_simp))
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apply safe
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apply (erule allE,erule allE,erule impE,erule_tac [2] allE,erule_tac [2] mp)
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prefer 2 apply assumption
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apply (fast elim: awp_mono)
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done
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lemma vc_complete: assumes der: "|- {P}c{Q}"
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  shows "(\<exists>ac. astrip ac = c & (\<forall>s. vc ac Q s) & (\<forall>s. P s --> awp ac Q s))"
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  (is "? ac. ?Eq P c Q ac")
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using der
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proof induct
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  case skip
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  show ?case (is "? ac. ?C ac")
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  proof show "?C Askip" by simp qed
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next
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  case (ass P a x)
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  show ?case (is "? ac. ?C ac")
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  proof show "?C(Aass x a)" by simp qed
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next
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  case (semi P Q R c1 c2)
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  from semi.hyps obtain ac1 where ih1: "?Eq P c1 Q ac1" by fast
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  from semi.hyps obtain ac2 where ih2: "?Eq Q c2 R ac2" by fast
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  show ?case (is "? ac. ?C ac")
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  proof
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    show "?C(Asemi ac1 ac2)"
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      using ih1 ih2 by simp (fast elim!: awp_mono vc_mono)
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  qed
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next
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  case (If P Q b c1 c2)
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  from If.hyps obtain ac1 where ih1: "?Eq (%s. P s & b s) c1 Q ac1" by fast
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  from If.hyps obtain ac2 where ih2: "?Eq (%s. P s & ~b s) c2 Q ac2" by fast
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  show ?case (is "? ac. ?C ac")
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  proof
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    show "?C(Aif b ac1 ac2)"
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      using ih1 ih2 by simp
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  qed
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next
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  case (While P b c)
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  from While.hyps obtain ac where ih: "?Eq (%s. P s & b s) c P ac" by fast
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  show ?case (is "? ac. ?C ac")
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  proof show "?C(Awhile b P ac)" using ih by simp qed
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next
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  case conseq thus ?case by(fast elim!: awp_mono vc_mono)
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qed
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lemma vcawp_vc_awp: "vcawp c Q = (vc c Q, awp c Q)"
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  by (induct c fixing: Q) (simp_all add: Let_def)
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end