(* Title: HOL/HOLCF/IMP/HoareEx.thy
Author: Tobias Nipkow, TUM
Copyright 1997 TUM
*)
section "Correctness of Hoare by Fixpoint Reasoning"
theory HoareEx imports Denotational begin
text \<open>
An example from the HOLCF paper by Mueller, Nipkow, Oheimb, Slotosch
@{cite MuellerNvOS99}. It demonstrates fixpoint reasoning by showing
the correctness of the Hoare rule for while-loops.
\<close>
type_synonym assn = "state => bool"
definition
hoare_valid :: "[assn, com, assn] => bool" ("|= {(1_)}/ (_)/ {(1_)}" 50) where
"|= {P} c {Q} = (\<forall>s t. P s \<and> D c $(Discr s) = Def t --> Q t)"
lemma WHILE_rule_sound:
"|= {A} c {A} ==> |= {A} WHILE b DO c {\<lambda>s. A s \<and> \<not> bval b s}"
apply (unfold hoare_valid_def)
apply (simp (no_asm))
apply (rule fix_ind)
apply (simp (no_asm)) \<comment> "simplifier with enhanced \<open>adm\<close>-tactic"
apply (simp (no_asm))
apply (simp (no_asm))
apply blast
done
end