src/HOL/Induct/Com.thy
author wenzelm
Fri Nov 25 21:14:34 2005 +0100 (2005-11-25)
changeset 18260 5597cfcecd49
parent 16417 9bc16273c2d4
child 19736 d8d0f8f51d69
permissions -rw-r--r--
tuned induct proofs;
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(*  Title:      HOL/Induct/Com
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    ID:         $Id$
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    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
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    Copyright   1997  University of Cambridge
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Example of Mutual Induction via Iteratived Inductive Definitions: Commands
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*)
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header{*Mutual Induction via Iteratived Inductive Definitions*}
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theory Com imports Main begin
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typedecl loc
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types  state = "loc => nat"
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       n2n2n = "nat => nat => nat"
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arities loc :: type
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datatype
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  exp = N nat
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      | X loc
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      | Op n2n2n exp exp
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      | valOf com exp          ("VALOF _ RESULTIS _"  60)
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and
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  com = SKIP
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      | ":="  loc exp          (infixl  60)
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      | Semi  com com          ("_;;_"  [60, 60] 60)
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      | Cond  exp com com      ("IF _ THEN _ ELSE _"  60)
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      | While exp com          ("WHILE _ DO _"  60)
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subsection {* Commands *}
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text{* Execution of commands *}
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consts  exec    :: "((exp*state) * (nat*state)) set => ((com*state)*state)set"
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syntax "@exec"  :: "((exp*state) * (nat*state)) set =>
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                    [com*state,state] => bool"     ("_/ -[_]-> _" [50,0,50] 50)
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translations  "csig -[eval]-> s" == "(csig,s) \<in> exec eval"
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syntax  eval'   :: "[exp*state,nat*state] =>
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                    ((exp*state) * (nat*state)) set => bool"
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                                           ("_/ -|[_]-> _" [50,0,50] 50)
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translations
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    "esig -|[eval]-> ns" => "(esig,ns) \<in> eval"
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text{*Command execution.  Natural numbers represent Booleans: 0=True, 1=False*}
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inductive "exec eval"
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  intros
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    Skip:    "(SKIP,s) -[eval]-> s"
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    Assign:  "(e,s) -|[eval]-> (v,s') ==> (x := e, s) -[eval]-> s'(x:=v)"
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    Semi:    "[| (c0,s) -[eval]-> s2; (c1,s2) -[eval]-> s1 |]
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             ==> (c0 ;; c1, s) -[eval]-> s1"
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    IfTrue: "[| (e,s) -|[eval]-> (0,s');  (c0,s') -[eval]-> s1 |]
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             ==> (IF e THEN c0 ELSE c1, s) -[eval]-> s1"
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    IfFalse: "[| (e,s) -|[eval]->  (Suc 0, s');  (c1,s') -[eval]-> s1 |]
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              ==> (IF e THEN c0 ELSE c1, s) -[eval]-> s1"
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    WhileFalse: "(e,s) -|[eval]-> (Suc 0, s1)
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                 ==> (WHILE e DO c, s) -[eval]-> s1"
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    WhileTrue:  "[| (e,s) -|[eval]-> (0,s1);
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                    (c,s1) -[eval]-> s2;  (WHILE e DO c, s2) -[eval]-> s3 |]
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                 ==> (WHILE e DO c, s) -[eval]-> s3"
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declare exec.intros [intro]
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inductive_cases
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        [elim!]: "(SKIP,s) -[eval]-> t"
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    and [elim!]: "(x:=a,s) -[eval]-> t"
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    and [elim!]: "(c1;;c2, s) -[eval]-> t"
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    and [elim!]: "(IF e THEN c1 ELSE c2, s) -[eval]-> t"
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    and exec_WHILE_case: "(WHILE b DO c,s) -[eval]-> t"
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text{*Justifies using "exec" in the inductive definition of "eval"*}
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lemma exec_mono: "A<=B ==> exec(A) <= exec(B)"
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apply (unfold exec.defs )
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apply (rule lfp_mono)
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apply (assumption | rule basic_monos)+
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done
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ML {*
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Unify.trace_bound := 30;
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Unify.search_bound := 60;
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*}
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text{*Command execution is functional (deterministic) provided evaluation is*}
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theorem single_valued_exec: "single_valued ev ==> single_valued(exec ev)"
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apply (simp add: single_valued_def)
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apply (intro allI)
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apply (rule impI)
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apply (erule exec.induct)
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apply (blast elim: exec_WHILE_case)+
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done
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subsection {* Expressions *}
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text{* Evaluation of arithmetic expressions *}
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consts  eval    :: "((exp*state) * (nat*state)) set"
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       "-|->"   :: "[exp*state,nat*state] => bool"         (infixl 50)
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translations
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    "esig -|-> (n,s)" <= "(esig,n,s) \<in> eval"
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    "esig -|-> ns"    == "(esig,ns ) \<in> eval"
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inductive eval
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  intros
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    N [intro!]: "(N(n),s) -|-> (n,s)"
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    X [intro!]: "(X(x),s) -|-> (s(x),s)"
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    Op [intro]: "[| (e0,s) -|-> (n0,s0);  (e1,s0)  -|-> (n1,s1) |]
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                 ==> (Op f e0 e1, s) -|-> (f n0 n1, s1)"
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    valOf [intro]: "[| (c,s) -[eval]-> s0;  (e,s0)  -|-> (n,s1) |]
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                    ==> (VALOF c RESULTIS e, s) -|-> (n, s1)"
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  monos exec_mono
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inductive_cases
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        [elim!]: "(N(n),sigma) -|-> (n',s')"
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    and [elim!]: "(X(x),sigma) -|-> (n,s')"
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    and [elim!]: "(Op f a1 a2,sigma)  -|-> (n,s')"
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    and [elim!]: "(VALOF c RESULTIS e, s) -|-> (n, s1)"
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lemma var_assign_eval [intro!]: "(X x, s(x:=n)) -|-> (n, s(x:=n))"
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by (rule fun_upd_same [THEN subst], fast)
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text{* Make the induction rule look nicer -- though eta_contract makes the new
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    version look worse than it is...*}
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lemma split_lemma:
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     "{((e,s),(n,s')). P e s n s'} = Collect (split (%v. split (split P v)))"
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by auto
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text{*New induction rule.  Note the form of the VALOF induction hypothesis*}
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lemma eval_induct
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  [case_names N X Op valOf, consumes 1, induct set: eval]:
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  "[| (e,s) -|-> (n,s');
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      !!n s. P (N n) s n s;
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      !!s x. P (X x) s (s x) s;
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      !!e0 e1 f n0 n1 s s0 s1.
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         [| (e0,s) -|-> (n0,s0); P e0 s n0 s0;
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            (e1,s0) -|-> (n1,s1); P e1 s0 n1 s1
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         |] ==> P (Op f e0 e1) s (f n0 n1) s1;
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      !!c e n s s0 s1.
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         [| (c,s) -[eval Int {((e,s),(n,s')). P e s n s'}]-> s0;
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            (c,s) -[eval]-> s0;
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            (e,s0) -|-> (n,s1); P e s0 n s1 |]
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         ==> P (VALOF c RESULTIS e) s n s1
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   |] ==> P e s n s'"
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apply (induct set: eval)
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apply blast
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apply blast
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apply blast
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apply (frule Int_lower1 [THEN exec_mono, THEN subsetD])
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apply (auto simp add: split_lemma)
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done
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text{*Lemma for Function_eval.  The major premise is that (c,s) executes to s1
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  using eval restricted to its functional part.  Note that the execution
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  (c,s) -[eval]-> s2 can use unrestricted eval!  The reason is that
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  the execution (c,s) -[eval Int {...}]-> s1 assures us that execution is
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  functional on the argument (c,s).
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*}
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lemma com_Unique:
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 "(c,s) -[eval Int {((e,s),(n,t)). \<forall>nt'. (e,s) -|-> nt' --> (n,t)=nt'}]-> s1
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  ==> \<forall>s2. (c,s) -[eval]-> s2 --> s2=s1"
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apply (induct set: exec)
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      apply simp_all
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      apply blast
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     apply force
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    apply blast
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   apply blast
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  apply blast
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 apply (blast elim: exec_WHILE_case)
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apply (erule_tac V = "(?c,s2) -[?ev]-> s3" in thin_rl)
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apply clarify
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apply (erule exec_WHILE_case, blast+)
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done
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text{*Expression evaluation is functional, or deterministic*}
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theorem single_valued_eval: "single_valued eval"
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apply (unfold single_valued_def)
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apply (intro allI, rule impI)
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apply (simp (no_asm_simp) only: split_tupled_all)
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apply (erule eval_induct)
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apply (drule_tac [4] com_Unique)
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apply (simp_all (no_asm_use))
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apply blast+
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done
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lemma eval_N_E [dest!]: "(N n, s) -|-> (v, s') ==> (v = n & s' = s)"
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  by (induct e == "N n" s v s' set: eval) simp_all
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text{*This theorem says that "WHILE TRUE DO c" cannot terminate*}
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lemma while_true_E:
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    "(c', s) -[eval]-> t ==> c' = WHILE (N 0) DO c ==> False"
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  by (induct set: exec) auto
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subsection{* Equivalence of IF e THEN c;;(WHILE e DO c) ELSE SKIP  and
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       WHILE e DO c *}
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lemma while_if1:
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     "(c',s) -[eval]-> t
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      ==> c' = WHILE e DO c ==>
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          (IF e THEN c;;c' ELSE SKIP, s) -[eval]-> t"
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  by (induct set: exec) auto
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lemma while_if2:
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     "(c',s) -[eval]-> t
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      ==> c' = IF e THEN c;;(WHILE e DO c) ELSE SKIP ==>
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          (WHILE e DO c, s) -[eval]-> t"
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  by (induct set: exec) auto
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theorem while_if:
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     "((IF e THEN c;;(WHILE e DO c) ELSE SKIP, s) -[eval]-> t)  =
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      ((WHILE e DO c, s) -[eval]-> t)"
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by (blast intro: while_if1 while_if2)
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subsection{* Equivalence of  (IF e THEN c1 ELSE c2);;c
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                         and  IF e THEN (c1;;c) ELSE (c2;;c)   *}
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lemma if_semi1:
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     "(c',s) -[eval]-> t
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      ==> c' = (IF e THEN c1 ELSE c2);;c ==>
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          (IF e THEN (c1;;c) ELSE (c2;;c), s) -[eval]-> t"
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  by (induct set: exec) auto
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lemma if_semi2:
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     "(c',s) -[eval]-> t
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      ==> c' = IF e THEN (c1;;c) ELSE (c2;;c) ==>
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          ((IF e THEN c1 ELSE c2);;c, s) -[eval]-> t"
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  by (induct set: exec) auto
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theorem if_semi: "(((IF e THEN c1 ELSE c2);;c, s) -[eval]-> t)  =
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                  ((IF e THEN (c1;;c) ELSE (c2;;c), s) -[eval]-> t)"
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  by (blast intro: if_semi1 if_semi2)
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subsection{* Equivalence of  VALOF c1 RESULTIS (VALOF c2 RESULTIS e)
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                  and  VALOF c1;;c2 RESULTIS e
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 *}
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lemma valof_valof1:
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     "(e',s) -|-> (v,s')
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      ==> e' = VALOF c1 RESULTIS (VALOF c2 RESULTIS e) ==>
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          (VALOF c1;;c2 RESULTIS e, s) -|-> (v,s')"
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  by (induct set: eval) auto
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lemma valof_valof2:
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     "(e',s) -|-> (v,s')
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      ==> e' = VALOF c1;;c2 RESULTIS e ==>
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          (VALOF c1 RESULTIS (VALOF c2 RESULTIS e), s) -|-> (v,s')"
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  by (induct set: eval) auto
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theorem valof_valof:
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     "((VALOF c1 RESULTIS (VALOF c2 RESULTIS e), s) -|-> (v,s'))  =
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      ((VALOF c1;;c2 RESULTIS e, s) -|-> (v,s'))"
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  by (blast intro: valof_valof1 valof_valof2)
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subsection{* Equivalence of  VALOF SKIP RESULTIS e  and  e *}
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lemma valof_skip1:
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     "(e',s) -|-> (v,s')
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      ==> e' = VALOF SKIP RESULTIS e ==>
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          (e, s) -|-> (v,s')"
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  by (induct set: eval) auto
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lemma valof_skip2:
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    "(e,s) -|-> (v,s') ==> (VALOF SKIP RESULTIS e, s) -|-> (v,s')"
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  by blast
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theorem valof_skip:
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    "((VALOF SKIP RESULTIS e, s) -|-> (v,s'))  =  ((e, s) -|-> (v,s'))"
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  by (blast intro: valof_skip1 valof_skip2)
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subsection{* Equivalence of  VALOF x:=e RESULTIS x  and  e *}
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lemma valof_assign1:
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     "(e',s) -|-> (v,s'')
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      ==> e' = VALOF x:=e RESULTIS X x ==>
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          (\<exists>s'. (e, s) -|-> (v,s') & (s'' = s'(x:=v)))"
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  by (induct set: eval) (simp_all del: fun_upd_apply, clarify, auto)
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lemma valof_assign2:
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    "(e,s) -|-> (v,s') ==> (VALOF x:=e RESULTIS X x, s) -|-> (v,s'(x:=v))"
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  by blast
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end