src/HOL/IMP/Def_Ass_Sound_Small.thy

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/IMP/Def_Ass_Sound_Small.thy	Mon Jun 06 16:29:38 2011 +0200
@@ -0,0 +1,56 @@
+(* Author: Tobias Nipkow *)
+
+theory Def_Ass_Sound_Small imports Def_Ass Def_Ass_Small
+begin
+
+subsection "Soundness wrt Small Steps"
+
+theorem progress:
+  "D (dom s) c A' \<Longrightarrow> c \<noteq> SKIP \<Longrightarrow> EX cs'. (c,s) \<rightarrow> cs'"
+proof (induct c arbitrary: s A')
+  case Assign thus ?case by auto (metis aval_Some small_step.Assign)
+next
+  case (If b c1 c2)
+  then obtain bv where "bval b s = Some bv" by (auto dest!:bval_Some)
+  then show ?case
+    by(cases bv)(auto intro: small_step.IfTrue small_step.IfFalse)
+qed (fastsimp intro: small_step.intros)+
+
+lemma D_mono:  "D A c M \<Longrightarrow> A \<subseteq> A' \<Longrightarrow> EX M'. D A' c M' & M <= M'"
+proof (induct c arbitrary: A A' M)
+  case Semi thus ?case by auto (metis D.intros(3))
+next
+  case (If b c1 c2)
+  then obtain M1 M2 where "vars b \<subseteq> A" "D A c1 M1" "D A c2 M2" "M = M1 \<inter> M2"
+    by auto
+  with If.hyps `A \<subseteq> A'` obtain M1' M2'
+    where "D A' c1 M1'" "D A' c2 M2'" and "M1 \<subseteq> M1'" "M2 \<subseteq> M2'" by metis
+  hence "D A' (IF b THEN c1 ELSE c2) (M1' \<inter> M2')" and "M \<subseteq> M1' \<inter> M2'"
+    using `vars b \<subseteq> A` `A \<subseteq> A'` `M = M1 \<inter> M2` by(fastsimp intro: D.intros)+
+  thus ?case by metis
+next
+  case While thus ?case by auto (metis D.intros(5) subset_trans)
+qed (auto intro: D.intros)
+
+theorem D_preservation:
+  "(c,s) \<rightarrow> (c',s') \<Longrightarrow> D (dom s) c A \<Longrightarrow> EX A'. D (dom s') c' A' & A <= A'"
+proof (induct arbitrary: A rule: small_step_induct)
+  case (While b c s)
+  then obtain A' where "vars b \<subseteq> dom s" "A = dom s" "D (dom s) c A'" by blast
+  moreover
+  then obtain A'' where "D A' c A''" by (metis D_incr D_mono)
+  ultimately have "D (dom s) (IF b THEN c; WHILE b DO c ELSE SKIP) (dom s)"
+    by (metis D.If[OF `vars b \<subseteq> dom s` D.Semi[OF `D (dom s) c A'` D.While[OF _ `D A' c A''`]] D.Skip] D_incr Int_absorb1 subset_trans)
+  thus ?case by (metis D_incr `A = dom s`)
+next
+  case Semi2 thus ?case by auto (metis D_mono D.intros(3))
+qed (auto intro: D.intros)
+
+theorem D_sound:
+  "(c,s) \<rightarrow>* (c',s') \<Longrightarrow> D (dom s) c A' \<Longrightarrow> c' \<noteq> SKIP
+   \<Longrightarrow> \<exists>cs''. (c',s') \<rightarrow> cs''"
+apply(induct arbitrary: A' rule:star_induct)
+apply (metis progress)
+by (metis D_preservation)
+
+end