(* Title: HOL/Hoare/SchorrWaite.thy
ID: $Id$
Author: Farhad Mehta
Copyright 2003 TUM
Proof of the Schorr-Waite graph marking algorithm.
*)
theory SchorrWaite = HeapSyntax:
section {* Machinery for the Schorr-Waite proof*}
constdefs
-- "Relations induced by a mapping"
rel :: "('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<times> 'a) set"
"rel m == {(x,y). m x = Ref y}"
relS :: "('a \<Rightarrow> 'a ref) set \<Rightarrow> ('a \<times> 'a) set"
"relS M == (\<Union> m \<in> M. rel m)"
addrs :: "'a ref set \<Rightarrow> 'a set"
"addrs P == {a. Ref a \<in> P}"
reachable :: "('a \<times> 'a) set \<Rightarrow> 'a ref set \<Rightarrow> 'a set"
"reachable r P == (r\<^sup>* `` addrs P)"
lemmas rel_defs = relS_def rel_def
text {* Rewrite rules for relations induced by a mapping*}
lemma self_reachable: "b \<in> B \<Longrightarrow> b \<in> R\<^sup>* `` B"
apply blast
done
lemma oneStep_reachable: "b \<in> R``B \<Longrightarrow> b \<in> R\<^sup>* `` B"
apply blast
done
lemma still_reachable: "\<lbrakk>B\<subseteq>Ra\<^sup>*``A; \<forall> (x,y) \<in> Rb-Ra. y\<in> (Ra\<^sup>*``A)\<rbrakk> \<Longrightarrow> Rb\<^sup>* `` B \<subseteq> Ra\<^sup>* `` A "
apply (clarsimp simp only:Image_iff intro:subsetI)
apply (erule rtrancl_induct)
apply blast
apply (subgoal_tac "(y, z) \<in> Ra\<union>(Rb-Ra)")
apply (erule UnE)
apply (auto intro:rtrancl_into_rtrancl)
apply blast
done
lemma still_reachable_eq: "\<lbrakk> A\<subseteq>Rb\<^sup>*``B; B\<subseteq>Ra\<^sup>*``A; \<forall> (x,y) \<in> Ra-Rb. y \<in>(Rb\<^sup>*``B); \<forall> (x,y) \<in> Rb-Ra. y\<in> (Ra\<^sup>*``A)\<rbrakk> \<Longrightarrow> Ra\<^sup>*``A = Rb\<^sup>*``B "
apply (rule equalityI)
apply (erule still_reachable ,assumption)+
done
lemma reachable_null: "reachable mS {Null} = {}"
apply (simp add: reachable_def addrs_def)
done
lemma reachable_empty: "reachable mS {} = {}"
apply (simp add: reachable_def addrs_def)
done
lemma reachable_union: "(reachable mS aS \<union> reachable mS bS) = reachable mS (aS \<union> bS)"
apply (simp add: reachable_def rel_defs addrs_def)
apply blast
done
lemma reachable_union_sym: "reachable r (insert a aS) = (r\<^sup>* `` addrs {a}) \<union> reachable r aS"
apply (simp add: reachable_def rel_defs addrs_def)
apply blast
done
lemma rel_upd1: "(a,b) \<notin> rel (r(q:=t)) \<Longrightarrow> (a,b) \<in> rel r \<Longrightarrow> a=q"
apply (rule classical)
apply (simp add:rel_defs fun_upd_apply)
done
lemma rel_upd2: "(a,b) \<notin> rel r \<Longrightarrow> (a,b) \<in> rel (r(q:=t)) \<Longrightarrow> a=q"
apply (rule classical)
apply (simp add:rel_defs fun_upd_apply)
done
constdefs
-- "Restriction of a relation"
restr ::"('a \<times> 'a) set \<Rightarrow> ('a \<Rightarrow> bool) \<Rightarrow> ('a \<times> 'a) set" ("(_/ | _)" [50, 51] 50)
"restr r m == {(x,y). (x,y) \<in> r \<and> \<not> m x}"
text {* Rewrite rules for the restriction of a relation *}
lemma restr_identity[simp]:
" (\<forall>x. \<not> m x) \<Longrightarrow> (R |m) = R"
by (auto simp add:restr_def)
lemma restr_rtrancl[simp]: " \<lbrakk>m l\<rbrakk> \<Longrightarrow> (R | m)\<^sup>* `` {l} = {l}"
by (auto simp add:restr_def elim:converse_rtranclE)
lemma [simp]: " \<lbrakk>m l\<rbrakk> \<Longrightarrow> (l,x) \<in> (R | m)\<^sup>* = (l=x)"
by (auto simp add:restr_def elim:converse_rtranclE)
lemma restr_upd: "((rel (r (q := t)))|(m(q := True))) = ((rel (r))|(m(q := True))) "
apply (auto simp:restr_def rel_def fun_upd_apply)
apply (rename_tac a b)
apply (case_tac "a=q")
apply auto
done
lemma restr_un: "((r \<union> s)|m) = (r|m) \<union> (s|m)"
by (auto simp add:restr_def)
lemma rel_upd3: "(a, b) \<notin> (r|(m(q := t))) \<Longrightarrow> (a,b) \<in> (r|m) \<Longrightarrow> a = q "
apply (rule classical)
apply (simp add:restr_def fun_upd_apply)
done
constdefs
-- "A short form for the stack mapping function for List"
S :: "('a \<Rightarrow> bool) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<Rightarrow> 'a ref)"
"S c l r == (\<lambda>x. if c x then r x else l x)"
text {* Rewrite rules for Lists using S as their mapping *}
lemma [rule_format,simp]:
"\<forall>p. a \<notin> set stack \<longrightarrow> List (S c l r) p stack = List (S (c(a:=x)) (l(a:=y)) (r(a:=z))) p stack"
apply(induct_tac stack)
apply(simp add:fun_upd_apply S_def)+
done
lemma [rule_format,simp]:
"\<forall>p. a \<notin> set stack \<longrightarrow> List (S c l (r(a:=z))) p stack = List (S c l r) p stack"
apply(induct_tac stack)
apply(simp add:fun_upd_apply S_def)+
done
lemma [rule_format,simp]:
"\<forall>p. a \<notin> set stack \<longrightarrow> List (S c (l(a:=z)) r) p stack = List (S c l r) p stack"
apply(induct_tac stack)
apply(simp add:fun_upd_apply S_def)+
done
lemma [rule_format,simp]:
"\<forall>p. a \<notin> set stack \<longrightarrow> List (S (c(a:=z)) l r) p stack = List (S c l r) p stack"
apply(induct_tac stack)
apply(simp add:fun_upd_apply S_def)+
done
consts
--"Recursive definition of what is means for a the graph/stack structure to be reconstructible"
stkOk :: "('a \<Rightarrow> bool) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> ('a \<Rightarrow> 'a ref) \<Rightarrow> 'a ref \<Rightarrow>'a list \<Rightarrow> bool"
primrec
stkOk_nil: "stkOk c l r iL iR t [] = True"
stkOk_cons: "stkOk c l r iL iR t (p#stk) = (stkOk c l r iL iR (Ref p) (stk) \<and>
iL p = (if c p then l p else t) \<and>
iR p = (if c p then t else r p))"
text {* Rewrite rules for stkOk *}
lemma [simp]: "\<And>t. \<lbrakk> x \<notin> set xs; Ref x\<noteq>t \<rbrakk> \<Longrightarrow>
stkOk (c(x := f)) l r iL iR t xs = stkOk c l r iL iR t xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
lemma [simp]: "\<And>t. \<lbrakk> x \<notin> set xs; Ref x\<noteq>t \<rbrakk> \<Longrightarrow>
stkOk c (l(x := g)) r iL iR t xs = stkOk c l r iL iR t xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
lemma [simp]: "\<And>t. \<lbrakk> x \<notin> set xs; Ref x\<noteq>t \<rbrakk> \<Longrightarrow>
stkOk c l (r(x := g)) iL iR t xs = stkOk c l r iL iR t xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
lemma stkOk_r_rewrite [simp]: "\<And>x. x \<notin> set xs \<Longrightarrow>
stkOk c l (r(x := g)) iL iR (Ref x) xs = stkOk c l r iL iR (Ref x) xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
lemma [simp]: "\<And>x. x \<notin> set xs \<Longrightarrow>
stkOk c (l(x := g)) r iL iR (Ref x) xs = stkOk c l r iL iR (Ref x) xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
lemma [simp]: "\<And>x. x \<notin> set xs \<Longrightarrow>
stkOk (c(x := g)) l r iL iR (Ref x) xs = stkOk c l r iL iR (Ref x) xs"
apply (induct xs)
apply (auto simp:eq_sym_conv)
done
section{*The Schorr-Waite algorithm*}
theorem SchorrWaiteAlgorithm:
"VARS c m l r t p q root
{R = reachable (relS {l, r}) {root} \<and> (\<forall>x. \<not> m x) \<and> iR = r \<and> iL = l}
t := root; p := Null;
WHILE p \<noteq> Null \<or> t \<noteq> Null \<and> \<not> t^.m
INV {\<exists>stack.
List (S c l r) p stack \<and> (*i1*)
(\<forall>x \<in> set stack. m x) \<and> (*i2*)
R = reachable (relS{l, r}) {t,p} \<and> (*i3*)
(\<forall>x. x \<in> R \<and> \<not>m x \<longrightarrow> (*i4*)
x \<in> reachable (relS{l,r}|m) ({t}\<union>set(map r stack))) \<and>
(\<forall>x. m x \<longrightarrow> x \<in> R) \<and> (*i5*)
(\<forall>x. x \<notin> set stack \<longrightarrow> r x = iR x \<and> l x = iL x) \<and> (*i6*)
(stkOk c l r iL iR t stack) (*i7*) }
DO IF t = Null \<or> t^.m
THEN IF p^.c
THEN q := t; t := p; p := p^.r; t^.r := q (*pop*)
ELSE q := t; t := p^.r; p^.r := p^.l; (*swing*)
p^.l := q; p^.c := True FI
ELSE q := p; p := t; t := t^.l; p^.l := q; (*push*)
p^.m := True; p^.c := False FI OD
{(\<forall>x. (x \<in> R) = m x) \<and> (r = iR \<and> l = iL) }"
(is "VARS c m l r t p q root {?Pre c m l r root} (?c1; ?c2; ?c3) {?Post c m l r}")
proof (vcg)
let "While {(c, m, l, r, t, p, q, root). ?whileB m t p}
{(c, m, l, r, t, p, q, root). ?inv c m l r t p} ?body" = ?c3
{
fix c m l r t p q root
assume "?Pre c m l r root"
thus "?inv c m l r root Null" by (auto simp add: reachable_def addrs_def)
next
fix c m l r t p q
let "\<exists>stack. ?Inv stack" = "?inv c m l r t p"
assume a: "?inv c m l r t p \<and> \<not>(p \<noteq> Null \<or> t \<noteq> Null \<and> \<not> t^.m)"
then obtain stack where inv: "?Inv stack" by blast
from a have pNull: "p = Null" and tDisj: "t=Null \<or> (t\<noteq>Null \<and> t^.m )" by auto
let "?I1 \<and> _ \<and> _ \<and> ?I4 \<and> ?I5 \<and> ?I6 \<and> _" = "?Inv stack"
from inv have i1: "?I1" and i4: "?I4" and i5: "?I5" and i6: "?I6" by simp+
from pNull i1 have stackEmpty: "stack = []" by simp
from tDisj i4 have RisMarked[rule_format]: "\<forall>x. x \<in> R \<longrightarrow> m x" by(auto simp: reachable_def addrs_def stackEmpty)
from i5 i6 show "(\<forall>x.(x \<in> R) = m x) \<and> r = iR \<and> l = iL" by(auto simp: stackEmpty expand_fun_eq intro:RisMarked)
next
fix c m l r t p q root
let "\<exists>stack. ?Inv stack" = "?inv c m l r t p"
let "\<exists>stack. ?popInv stack" = "?inv c m l (r(p \<rightarrow> t)) p (p^.r)"
let "\<exists>stack. ?swInv stack" =
"?inv (c(p \<rightarrow> True)) m (l(p \<rightarrow> t)) (r(p \<rightarrow> p^.l)) (p^.r) p"
let "\<exists>stack. ?puInv stack" =
"?inv (c(t \<rightarrow> False)) (m(t \<rightarrow> True)) (l(t \<rightarrow> p)) r (t^.l) t"
let "?ifB1" = "(t = Null \<or> t^.m)"
let "?ifB2" = "p^.c"
assume "(\<exists>stack.?Inv stack) \<and> (p \<noteq> Null \<or> t \<noteq> Null \<and> \<not> t^.m)" (is "_ \<and> ?whileB")
then obtain stack where inv: "?Inv stack" and whileB: "?whileB" by blast
let "?I1 \<and> ?I2 \<and> ?I3 \<and> ?I4 \<and> ?I5 \<and> ?I6 \<and> ?I7" = "?Inv stack"
from inv have i1: "?I1" and i2: "?I2" and i3: "?I3" and i4: "?I4"
and i5: "?I5" and i6: "?I6" and i7: "?I7" by simp+
have stackDist: "distinct (stack)" using i1 by (rule List_distinct)
show "(?ifB1 \<longrightarrow> (?ifB2 \<longrightarrow> (\<exists>stack.?popInv stack)) \<and>
(\<not>?ifB2 \<longrightarrow> (\<exists>stack.?swInv stack)) ) \<and>
(\<not>?ifB1 \<longrightarrow> (\<exists>stack.?puInv stack))"
proof -
{
assume ifB1: "t = Null \<or> t^.m" and ifB2: "p^.c"
from ifB1 whileB have pNotNull: "p \<noteq> Null" by auto
then obtain addr_p where addr_p_eq: "p = Ref addr_p" by auto
with i1 obtain stack_tl where stack_eq: "stack = (addr p) # stack_tl"
by auto
with i2 have m_addr_p: "p^.m" by auto
have stackDist: "distinct (stack)" using i1 by (rule List_distinct)
from stack_eq stackDist have p_notin_stack_tl: "addr p \<notin> set stack_tl" by simp
let "?poI1\<and> ?poI2\<and> ?poI3\<and> ?poI4\<and> ?poI5\<and> ?poI6\<and> ?poI7" = "?popInv stack_tl"
have "?popInv stack_tl"
proof -
-- {*List property is maintained:*}
from i1 p_notin_stack_tl ifB2
have poI1: "List (S c l (r(p \<rightarrow> t))) (p^.r) stack_tl"
by(simp add: addr_p_eq stack_eq, simp add: S_def)
moreover
-- {*Everything on the stack is marked:*}
from i2 have poI2: "\<forall> x \<in> set stack_tl. m x" by (simp add:stack_eq)
moreover
-- {*Everything is still reachable:*}
let "(R = reachable ?Ra ?A)" = "?I3"
let "?Rb" = "(relS {l, r(p \<rightarrow> t)})"
let "?B" = "{p, p^.r}"
-- {*Our goal is @{text"R = reachable ?Rb ?B"}.*}
have "?Ra\<^sup>* `` addrs ?A = ?Rb\<^sup>* `` addrs ?B" (is "?L = ?R")
proof
show "?L \<subseteq> ?R"
proof (rule still_reachable)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` addrs ?B" by(fastsimp simp:addrs_def relS_def rel_def addr_p_eq
intro:oneStep_reachable Image_iff[THEN iffD2])
show "\<forall>(x,y) \<in> ?Ra-?Rb. y \<in> (?Rb\<^sup>* `` addrs ?B)" by (clarsimp simp:relS_def)
(fastsimp simp add:rel_def Image_iff addrs_def dest:rel_upd1)
qed
show "?R \<subseteq> ?L"
proof (rule still_reachable)
show "addrs ?B \<subseteq> ?Ra\<^sup>* `` addrs ?A"
by(fastsimp simp:addrs_def rel_defs addr_p_eq
intro:oneStep_reachable Image_iff[THEN iffD2])
next
show "\<forall>(x, y)\<in>?Rb-?Ra. y\<in>(?Ra\<^sup>*``addrs ?A)"
by (clarsimp simp:relS_def)
(fastsimp simp add:rel_def Image_iff addrs_def dest:rel_upd2)
qed
qed
with i3 have poI3: "R = reachable ?Rb ?B" by (simp add:reachable_def)
moreover
-- "If it is reachable and not marked, it is still reachable using..."
let "\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Ra ?A" = ?I4
let "?Rb" = "relS {l, r(p \<rightarrow> t)} | m"
let "?B" = "{p} \<union> set (map (r(p \<rightarrow> t)) stack_tl)"
-- {*Our goal is @{text"\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Rb ?B"}.*}
let ?T = "{t, p^.r}"
have "?Ra\<^sup>* `` addrs ?A \<subseteq> ?Rb\<^sup>* `` (addrs ?B \<union> addrs ?T)"
proof (rule still_reachable)
have rewrite: "\<forall>s\<in>set stack_tl. (r(p \<rightarrow> t)) s = r s"
by (auto simp add:p_notin_stack_tl intro:fun_upd_other)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` (addrs ?B \<union> addrs ?T)"
by (fastsimp cong:map_cong simp:stack_eq addrs_def rewrite intro:self_reachable)
show "\<forall>(x, y)\<in>?Ra-?Rb. y\<in>(?Rb\<^sup>*``(addrs ?B \<union> addrs ?T))"
by (clarsimp simp:restr_def relS_def)
(fastsimp simp add:rel_def Image_iff addrs_def dest:rel_upd1)
qed
-- "We now bring a term from the right to the left of the subset relation."
hence subset: "?Ra\<^sup>* `` addrs ?A - ?Rb\<^sup>* `` addrs ?T \<subseteq> ?Rb\<^sup>* `` addrs ?B"
by blast
have poI4: "\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Rb ?B"
proof (rule allI, rule impI)
fix x
assume a: "x \<in> R \<and> \<not> m x"
-- {*First, a disjunction on @{term"p^.r"} used later in the proof*}
have pDisj:"p^.r = Null \<or> (p^.r \<noteq> Null \<and> p^.r^.m)" using poI1 poI2
by auto
-- {*@{term x} belongs to the left hand side of @{thm[source] subset}:*}
have incl: "x \<in> ?Ra\<^sup>*``addrs ?A" using a i4 by (simp only:reachable_def, clarsimp)
have excl: "x \<notin> ?Rb\<^sup>*`` addrs ?T" using pDisj ifB1 a by (auto simp add:addrs_def)
-- {*And therefore also belongs to the right hand side of @{thm[source]subset},*}
-- {*which corresponds to our goal.*}
from incl excl subset show "x \<in> reachable ?Rb ?B" by (auto simp add:reachable_def)
qed
moreover
-- "If it is marked, then it is reachable"
from i5 have poI5: "\<forall>x. m x \<longrightarrow> x \<in> R" .
moreover
-- {*If it is not on the stack, then its @{term l} and @{term r} fields are unchanged*}
from i7 i6 ifB2
have poI6: "\<forall>x. x \<notin> set stack_tl \<longrightarrow> (r(p \<rightarrow> t)) x = iR x \<and> l x = iL x"
by(auto simp: addr_p_eq stack_eq fun_upd_apply)
moreover
-- {*If it is on the stack, then its @{term l} and @{term r} fields can be reconstructed*}
from p_notin_stack_tl i7 have poI7: "stkOk c l (r(p \<rightarrow> t)) iL iR p stack_tl"
by (clarsimp simp:stack_eq addr_p_eq)
ultimately show "?popInv stack_tl" by simp
qed
hence "\<exists>stack. ?popInv stack" ..
}
moreover
-- "Proofs of the Swing and Push arm follow."
-- "Since they are in principle simmilar to the Pop arm proof,"
-- "we show fewer comments and use frequent pattern matching."
{
-- "Swing arm"
assume ifB1: "?ifB1" and nifB2: "\<not>?ifB2"
from ifB1 whileB have pNotNull: "p \<noteq> Null" by clarsimp
then obtain addr_p where addr_p_eq: "p = Ref addr_p" by clarsimp
with i1 obtain stack_tl where stack_eq: "stack = (addr p) # stack_tl" by clarsimp
with i2 have m_addr_p: "p^.m" by clarsimp
from stack_eq stackDist have p_notin_stack_tl: "(addr p) \<notin> set stack_tl"
by simp
let "?swI1\<and>?swI2\<and>?swI3\<and>?swI4\<and>?swI5\<and>?swI6\<and>?swI7" = "?swInv stack"
have "?swInv stack"
proof -
-- {*List property is maintained:*}
from i1 p_notin_stack_tl nifB2
have swI1: "?swI1"
by (simp add:addr_p_eq stack_eq, simp add:S_def)
moreover
-- {*Everything on the stack is marked:*}
from i2
have swI2: "?swI2" .
moreover
-- {*Everything is still reachable:*}
let "R = reachable ?Ra ?A" = "?I3"
let "R = reachable ?Rb ?B" = "?swI3"
have "?Ra\<^sup>* `` addrs ?A = ?Rb\<^sup>* `` addrs ?B"
proof (rule still_reachable_eq)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` addrs ?B"
by(fastsimp simp:addrs_def rel_defs addr_p_eq intro:oneStep_reachable Image_iff[THEN iffD2])
next
show "addrs ?B \<subseteq> ?Ra\<^sup>* `` addrs ?A"
by(fastsimp simp:addrs_def rel_defs addr_p_eq intro:oneStep_reachable Image_iff[THEN iffD2])
next
show "\<forall>(x, y)\<in>?Ra-?Rb. y\<in>(?Rb\<^sup>*``addrs ?B)"
by (clarsimp simp:relS_def) (fastsimp simp add:rel_def Image_iff addrs_def fun_upd_apply dest:rel_upd1)
next
show "\<forall>(x, y)\<in>?Rb-?Ra. y\<in>(?Ra\<^sup>*``addrs ?A)"
by (clarsimp simp:relS_def) (fastsimp simp add:rel_def Image_iff addrs_def fun_upd_apply dest:rel_upd2)
qed
with i3
have swI3: "?swI3" by (simp add:reachable_def)
moreover
-- "If it is reachable and not marked, it is still reachable using..."
let "\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Ra ?A" = ?I4
let "\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Rb ?B" = ?swI4
let ?T = "{t}"
have "?Ra\<^sup>*``addrs ?A \<subseteq> ?Rb\<^sup>*``(addrs ?B \<union> addrs ?T)"
proof (rule still_reachable)
have rewrite: "(\<forall>s\<in>set stack_tl. (r(addr p := l(addr p))) s = r s)"
by (auto simp add:p_notin_stack_tl intro:fun_upd_other)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` (addrs ?B \<union> addrs ?T)"
by (fastsimp cong:map_cong simp:stack_eq addrs_def rewrite intro:self_reachable)
next
show "\<forall>(x, y)\<in>?Ra-?Rb. y\<in>(?Rb\<^sup>*``(addrs ?B \<union> addrs ?T))"
by (clarsimp simp:relS_def restr_def) (fastsimp simp add:rel_def Image_iff addrs_def fun_upd_apply dest:rel_upd1)
qed
then have subset: "?Ra\<^sup>*``addrs ?A - ?Rb\<^sup>*``addrs ?T \<subseteq> ?Rb\<^sup>*``addrs ?B"
by blast
have ?swI4
proof (rule allI, rule impI)
fix x
assume a: "x \<in> R \<and>\<not> m x"
with i4 addr_p_eq stack_eq have inc: "x \<in> ?Ra\<^sup>*``addrs ?A"
by (simp only:reachable_def, clarsimp)
with ifB1 a
have exc: "x \<notin> ?Rb\<^sup>*`` addrs ?T"
by (auto simp add:addrs_def)
from inc exc subset show "x \<in> reachable ?Rb ?B"
by (auto simp add:reachable_def)
qed
moreover
-- "If it is marked, then it is reachable"
from i5
have "?swI5" .
moreover
-- {*If it is not on the stack, then its @{term l} and @{term r} fields are unchanged*}
from i6 stack_eq
have "?swI6"
by clarsimp
moreover
-- {*If it is on the stack, then its @{term l} and @{term r} fields can be reconstructed*}
from stackDist i7 nifB2
have "?swI7"
by (clarsimp simp:addr_p_eq stack_eq)
ultimately show ?thesis by auto
qed
then have "\<exists>stack. ?swInv stack" by blast
}
moreover
{
-- "Push arm"
assume nifB1: "\<not>?ifB1"
from nifB1 whileB have tNotNull: "t \<noteq> Null" by clarsimp
then obtain addr_t where addr_t_eq: "t = Ref addr_t" by clarsimp
with i1 obtain new_stack where new_stack_eq: "new_stack = (addr t) # stack" by clarsimp
from tNotNull nifB1 have n_m_addr_t: "\<not> (t^.m)" by clarsimp
with i2 have t_notin_stack: "(addr t) \<notin> set stack" by blast
let "?puI1\<and>?puI2\<and>?puI3\<and>?puI4\<and>?puI5\<and>?puI6\<and>?puI7" = "?puInv new_stack"
have "?puInv new_stack"
proof -
-- {*List property is maintained:*}
from i1 t_notin_stack
have puI1: "?puI1"
by (simp add:addr_t_eq new_stack_eq, simp add:S_def)
moreover
-- {*Everything on the stack is marked:*}
from i2
have puI2: "?puI2"
by (simp add:new_stack_eq fun_upd_apply)
moreover
-- {*Everything is still reachable:*}
let "R = reachable ?Ra ?A" = "?I3"
let "R = reachable ?Rb ?B" = "?puI3"
have "?Ra\<^sup>* `` addrs ?A = ?Rb\<^sup>* `` addrs ?B"
proof (rule still_reachable_eq)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` addrs ?B"
by(fastsimp simp:addrs_def rel_defs addr_t_eq intro:oneStep_reachable Image_iff[THEN iffD2])
next
show "addrs ?B \<subseteq> ?Ra\<^sup>* `` addrs ?A"
by(fastsimp simp:addrs_def rel_defs addr_t_eq intro:oneStep_reachable Image_iff[THEN iffD2])
next
show "\<forall>(x, y)\<in>?Ra-?Rb. y\<in>(?Rb\<^sup>*``addrs ?B)"
by (clarsimp simp:relS_def) (fastsimp simp add:rel_def Image_iff addrs_def dest:rel_upd1)
next
show "\<forall>(x, y)\<in>?Rb-?Ra. y\<in>(?Ra\<^sup>*``addrs ?A)"
by (clarsimp simp:relS_def) (fastsimp simp add:rel_def Image_iff addrs_def fun_upd_apply dest:rel_upd2)
qed
with i3
have puI3: "?puI3" by (simp add:reachable_def)
moreover
-- "If it is reachable and not marked, it is still reachable using..."
let "\<forall>x. x \<in> R \<and> \<not> m x \<longrightarrow> x \<in> reachable ?Ra ?A" = ?I4
let "\<forall>x. x \<in> R \<and> \<not> ?new_m x \<longrightarrow> x \<in> reachable ?Rb ?B" = ?puI4
let ?T = "{t}"
have "?Ra\<^sup>*``addrs ?A \<subseteq> ?Rb\<^sup>*``(addrs ?B \<union> addrs ?T)"
proof (rule still_reachable)
show "addrs ?A \<subseteq> ?Rb\<^sup>* `` (addrs ?B \<union> addrs ?T)"
by (fastsimp simp:new_stack_eq addrs_def intro:self_reachable)
next
show "\<forall>(x, y)\<in>?Ra-?Rb. y\<in>(?Rb\<^sup>*``(addrs ?B \<union> addrs ?T))"
by (clarsimp simp:relS_def new_stack_eq restr_un restr_upd)
(fastsimp simp add:rel_def Image_iff restr_def addrs_def fun_upd_apply addr_t_eq dest:rel_upd3)
qed
then have subset: "?Ra\<^sup>*``addrs ?A - ?Rb\<^sup>*``addrs ?T \<subseteq> ?Rb\<^sup>*``addrs ?B"
by blast
have ?puI4
proof (rule allI, rule impI)
fix x
assume a: "x \<in> R \<and> \<not> ?new_m x"
have xDisj: "x=(addr t) \<or> x\<noteq>(addr t)" by simp
with i4 a have inc: "x \<in> ?Ra\<^sup>*``addrs ?A"
by (fastsimp simp:addr_t_eq addrs_def reachable_def intro:self_reachable)
have exc: "x \<notin> ?Rb\<^sup>*`` addrs ?T"
using xDisj a n_m_addr_t
by (clarsimp simp add:addrs_def addr_t_eq)
from inc exc subset show "x \<in> reachable ?Rb ?B"
by (auto simp add:reachable_def)
qed
moreover
-- "If it is marked, then it is reachable"
from i5
have "?puI5"
by (auto simp:addrs_def i3 reachable_def addr_t_eq fun_upd_apply intro:self_reachable)
moreover
-- {*If it is not on the stack, then its @{term l} and @{term r} fields are unchanged*}
from i6
have "?puI6"
by (simp add:new_stack_eq)
moreover
-- {*If it is on the stack, then its @{term l} and @{term r} fields can be reconstructed*}
from stackDist i6 t_notin_stack i7
have "?puI7" by (clarsimp simp:addr_t_eq new_stack_eq)
ultimately show ?thesis by auto
qed
then have "\<exists>stack. ?puInv stack" by blast
}
ultimately show ?thesis by blast
qed
}
qed
end