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Homework 8

This is the task corresponding to homework 8.

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Definitions File

theory Defs
  imports "HOL-IMP.Small_Step" "HOL-IMP.Live_True"
begin

fun bury :: "com \<Rightarrow> vname set \<Rightarrow> com" where
"bury SKIP X = SKIP" |
"bury (x ::= a) X = (if x \<in> X then x ::= a else SKIP)" |
"bury (c\<^sub>1;; c\<^sub>2) X = (bury c\<^sub>1 (L c\<^sub>2 X);; bury c\<^sub>2 X)" |
"bury (IF b THEN c\<^sub>1 ELSE c\<^sub>2) X = IF b THEN bury c\<^sub>1 X ELSE bury c\<^sub>2 X" |
"bury (WHILE b DO c) X = WHILE b DO bury c (L (WHILE b DO c) X)"


end

Template File

theory Submission
  imports Defs
begin

theorem lfp_eq: "\<lbrakk> mono f; mono g; lfp f \<subseteq> U; lfp g \<subseteq> U;
  \<And>X. X \<subseteq> U \<Longrightarrow> f X = g X \<rbrakk> \<Longrightarrow> lfp f = lfp g"
  sorry

lemmas [simp] = L.simps(5)
lemmas L_mono2 = L_mono[unfolded mono_def]

theorem L_bury[simp]: "X \<subseteq> Y \<Longrightarrow> L (bury c Y) X = L c X"
proof(induction c arbitrary: X Y)
sorry
qed

theorem bury_bury: "X \<subseteq> Y \<Longrightarrow> bury (bury c Y) X = bury c X"
  sorry

corollary "bury (bury c X) X = bury c X"
end

Check File

theory Check
  imports Submission
begin

theorem lfp_eq: "\<lbrakk> mono f; mono g; lfp f \<subseteq> U; lfp g \<subseteq> U;
  \<And>X. X \<subseteq> U \<Longrightarrow> f X = g X \<rbrakk> \<Longrightarrow> lfp f = lfp g"
  by (rule Submission.lfp_eq)

theorem L_bury: "X \<subseteq> Y \<Longrightarrow> L (bury c Y) X = L c X"
  by (rule Submission.L_bury)

theorem bury_bury: "X \<subseteq> Y \<Longrightarrow> bury (bury c Y) X = bury c X"
  by (rule Submission.bury_bury)

end

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