
diff -r 8f8db701f69f -r a95987e9c7e9 thys/turing_basic.thy
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/thys/turing_basic.thy	Sun Jan 13 09:57:28 2013 +0000
@@ -0,0 +1,350 @@
+(* Title: Turing machines
+   Author: Xu Jian <xujian817@hotmail.com>
+   Maintainer: Xu Jian
+*)
+
+theory turing_basic
+imports Main
+begin
+
+section {* Basic definitions of Turing machine *}
+
+definition 
+  "iseven n \<equiv> \<exists>x. n = 2 * x"
+
+datatype action = W0 | W1 | L | R | Nop
+
+datatype cell = Bk | Oc
+
+type_synonym tape = "cell list \<times> cell list"
+
+type_synonym state = nat
+
+type_synonym instr = "action \<times> state"
+
+type_synonym tprog = "instr list"
+
+type_synonym config = "state \<times> tape"
+
+fun nth_of where
+  "nth_of [] _ = None"
+| "nth_of (x # xs) 0 = Some x"
+| "nth_of (x # xs) (Suc n) = nth_of xs n" 
+
+fun 
+  fetch :: "tprog \<Rightarrow> state \<Rightarrow> cell \<Rightarrow> instr"
+where
+  "fetch p 0 b = (Nop, 0)"
+| "fetch p (Suc s) Bk = 
+     (case nth_of p (2 * s) of
+        Some i \<Rightarrow> i
+      | None \<Rightarrow> (Nop, 0))"
+|"fetch p (Suc s) Oc = 
+     (case nth_of p ((2 * s) + 1) of
+         Some i \<Rightarrow> i
+       | None \<Rightarrow> (Nop, 0))"
+
+fun 
+  update :: "action \<Rightarrow> tape \<Rightarrow> tape"
+where 
+  "update W0 (l, r) = (l, Bk # (tl r))" 
+| "update W1 (l, r) = (l, Oc # (tl r))"
+| "update L (l, r) = (if l = [] then ([], Bk # r) else (tl l, (hd l) # r))" 
+| "update R (l, r) = (if r = [] then (Bk # l, []) else ((hd r) # l, tl r))" 
+| "update Nop (l, r) = (l, r)"
+
+abbreviation 
+  "read r == if (r = []) then Bk else hd r"
+
+
+fun 
+  step :: "config \<Rightarrow> tprog \<Rightarrow> config"
+where
+  "step (s, l, r) p = (let (a, s') = fetch p s (read r) in (s', update a (l, r)))"
+
+fun steps :: "config \<Rightarrow> tprog \<Rightarrow> nat \<Rightarrow> config"
+  where
+  "steps c p 0 = c" |
+  "steps c p (Suc n) = steps (step c p) p n"
+
+lemma step_red [simp]: 
+  shows "steps c p (Suc n) = step (steps c p n) p"
+by (induct n arbitrary: c) (auto)
+
+lemma steps_add [simp]: 
+  shows "steps c p (m + n) = steps (steps c p m) p n"
+by (induct m arbitrary: c) (auto)
+
+definition 
+  tm_wf :: "tprog \<Rightarrow> bool"
+where
+  "tm_wf p = (length p \<ge> 2 \<and> iseven (length p) \<and> (\<forall>(a, s) \<in> set p. s \<le> length p div 2))"
+
+(* FIXME: needed? *)
+lemma halt_lemma: 
+  "\<lbrakk>wf LE; \<forall>n. (\<not> P (f n) \<longrightarrow> (f (Suc n), (f n)) \<in> LE)\<rbrakk> \<Longrightarrow> \<exists>n. P (f n)"
+by (metis wf_iff_no_infinite_down_chain)
+
+abbreviation exponent :: "'a \<Rightarrow> nat \<Rightarrow> 'a list" ("_ \<up> _" [100, 99] 100)
+  where "x \<up> n == replicate n x"
+
+definition tinres :: "cell list \<Rightarrow> cell list \<Rightarrow> bool"
+  where
+  "tinres xs ys = (\<exists>n. xs = ys @ Bk \<up> n \<or> ys = xs @ Bk \<up> n)"
+
+fun 
+  shift :: "tprog \<Rightarrow> nat \<Rightarrow> tprog"
+where
+  "shift p n = (map (\<lambda> (a, s). (a, (if s = 0 then 0 else s + n))) p)"
+
+
+lemma [simp]: 
+  "length (shift p n) = length p"
+by (simp)
+
+fun 
+  adjust :: "tprog \<Rightarrow> tprog"
+where
+  "adjust p = (map (\<lambda> (a, s). (a, if s = 0 then ((length p) div 2) + 1 else s)) p)"
+
+lemma [simp]: 
+  shows "length (adjust p) = length p"
+by (simp)
+
+definition
+  tm_comp :: "tprog \<Rightarrow> tprog \<Rightarrow> tprog" ("_ |+| _" [0, 0] 100)
+where
+  "tm_comp p1 p2 = ((adjust p1) @ (shift p2 ((length p1) div 2)))"
+
+fun
+  is_final :: "config \<Rightarrow> bool"
+where
+  "is_final (s, l, r) = (s = 0)"
+
+fun 
+  holds_for :: "(tape \<Rightarrow> bool) \<Rightarrow> config \<Rightarrow> bool" ("_ holds'_for _" [100, 99] 100)
+where
+  "P holds_for (s, l, r) = P (l, r)"  
+
+lemma step_0 [simp]: 
+  shows "step (0, (l, r)) p = (0, (l, r))"
+by simp
+
+lemma steps_0 [simp]: 
+  shows "steps (0, (l, r)) p n = (0, (l, r))"
+by (induct n) (simp_all)
+
+type_synonym assert = "tape \<Rightarrow> bool"
+
+definition assert_imp :: "assert \<Rightarrow> assert \<Rightarrow> bool" ("_ \<mapsto> _" [0, 0] 100)
+  where
+  "assert_imp P Q = (\<forall>l r. P (l, r) \<longrightarrow> Q (l, r))"
+
+definition
+  Hoare :: "assert \<Rightarrow> tprog \<Rightarrow> assert \<Rightarrow> bool" ("({(1_)}/ (_)/ {(1_)})" 50)
+where
+  "{P} p {Q} \<equiv> 
+     (\<forall>l r. P (l, r) \<longrightarrow> (\<exists>n. is_final (steps (1, (l, r)) p n) \<and> Q holds_for (steps (1, (l, r)) p n)))"
+
+lemma HoareI:
+  assumes "\<And>l r. P (l, r) \<Longrightarrow> \<exists>n. is_final (steps (1, (l, r)) p n) \<and> Q holds_for (steps (1, (l, r)) p n)"
+  shows "{P} p {Q}"
+unfolding Hoare_def using assms by auto
+
+lemma HoareI2:
+  assumes "\<And>l r n. P (l, r) \<and> is_final (steps (1, (l, r)) p n) \<and> Q holds_for (steps (1, (l, r)) p n)"
+  shows "{P} p {Q}"
+unfolding Hoare_def using assms by auto
+
+text {*
+{P1} A {Q1}   {P2} B {Q2}  Q1 \<mapsto> P2
+-----------------------------------
+    {P1} A |+| B {Q2}
+*}
+
+
+lemma Hoare_plus: 
+  assumes aimpb: "Q1 \<mapsto> P2"
+  and A_wf : "tm_wf A"
+  and B_wf : "tm_wf B"
+  and A_halt : "{P1} A {Q1}"
+  and B_halt : "{P2} B {Q2}"
+  shows "{P1} A |+| B {Q2}"
+proof(rule HoareI)
+  fix a b
+  assume h: "P1 (a, b)"
+  hence "\<exists>n. let (s, tp') = steps (Suc 0, a, b) A n in s = 0 \<and> Q1 tp'"
+    using A_halt unfolding hoare_def by simp
+  from this obtain stp1 where "let (s, tp') = steps (Suc 0, a, b) A stp1 in s = 0 \<and> Q1 tp'" ..
+  then show "\<exists>n. case steps (Suc 0, a, b) (A |+| B) n of (s, tp') \<Rightarrow> s = 0 \<and> Q2 tp'"
+  proof(case_tac "steps (Suc 0, a, b) A stp1", simp, erule_tac conjE)
+    fix aa ba c
+    assume g1: "Q1 (ba, c)" 
+      and g2: "steps (Suc 0, a, b) A stp1 = (0, ba, c)"
+    hence "P2 (ba, c)"
+      using aimpb apply(simp add: assert_imp_def)
+      done
+    hence "\<exists> stp. let (s, tp') = steps (Suc 0, ba, c) B stp in s = 0 \<and> Q2 tp'"
+      using B_halt unfolding hoare_def by simp
+    from this obtain stp2 where "let (s, tp') = steps (Suc 0, ba, c) B stp2 in s = 0 \<and> Q2 tp'" ..
+    thus "?thesis"
+    proof(case_tac "steps (Suc 0, ba, c) B stp2", simp, erule_tac conjE)
+      fix aa bb ca
+      assume g3: " Q2 (bb, ca)" "steps (Suc 0, ba, c) B stp2 = (0, bb, ca)"
+      have "\<exists> stp. steps (Suc 0, a, b) (A |+| B) stp = (Suc (length A div 2), ba , c)"
+        using g2 A_wf B_wf
+        sorry
+      moreover have "\<exists> stp. steps (Suc (length A div 2), ba, c) (A |+| B) stp = (0, bb, ca)"
+        using g3 A_wf B_wf
+        sorry
+      ultimately show "\<exists>n. case steps (Suc 0, a, b) (A |+| B) n of (s, tp') \<Rightarrow> s = 0 \<and> Q2 tp'"
+        apply(erule_tac exE, erule_tac exE)
+        apply(rule_tac x = "stp + stpa" in exI, simp)
+        using g3 by simp
+    qed
+  qed
+qed
+
+lemma hoare_plus: 
+  assumes A_wf : "tm_wf A"
+  and B_wf : "tm_wf B"
+  and A_halt : "{P1} A {Q1}"
+  and B_halt : "{P2} B {Q2}"
+  and aimpb: "Q1 \<mapsto> P2"
+  shows "{P1} A |+| B {Q2}"
+unfolding hoare_def
+proof(auto split: )
+  fix a b
+  assume h: "P1 (a, b)"
+  hence "\<exists>n. let (s, tp') = steps (Suc 0, a, b) A n in s = 0 \<and> Q1 tp'"
+    using A_halt unfolding hoare_def by simp
+  from this obtain stp1 where "let (s, tp') = steps (Suc 0, a, b) A stp1 in s = 0 \<and> Q1 tp'" ..
+  then show "\<exists>n. case steps (Suc 0, a, b) (A |+| B) n of (s, tp') \<Rightarrow> s = 0 \<and> Q2 tp'"
+  proof(case_tac "steps (Suc 0, a, b) A stp1", simp, erule_tac conjE)
+    fix aa ba c
+    assume g1: "Q1 (ba, c)" 
+      and g2: "steps (Suc 0, a, b) A stp1 = (0, ba, c)"
+    hence "P2 (ba, c)"
+      using aimpb apply(simp add: assert_imp_def)
+      done
+    hence "\<exists> stp. let (s, tp') = steps (Suc 0, ba, c) B stp in s = 0 \<and> Q2 tp'"
+      using B_halt unfolding hoare_def by simp
+    from this obtain stp2 where "let (s, tp') = steps (Suc 0, ba, c) B stp2 in s = 0 \<and> Q2 tp'" ..
+    thus "?thesis"
+    proof(case_tac "steps (Suc 0, ba, c) B stp2", simp, erule_tac conjE)
+      fix aa bb ca
+      assume g3: " Q2 (bb, ca)" "steps (Suc 0, ba, c) B stp2 = (0, bb, ca)"
+      have "\<exists> stp. steps (Suc 0, a, b) (A |+| B) stp = (Suc (length A div 2), ba , c)"
+        using g2 A_wf B_wf
+        sorry
+      moreover have "\<exists> stp. steps (Suc (length A div 2), ba, c) (A |+| B) stp = (0, bb, ca)"
+        using g3 A_wf B_wf
+        sorry
+      ultimately show "\<exists>n. case steps (Suc 0, a, b) (A |+| B) n of (s, tp') \<Rightarrow> s = 0 \<and> Q2 tp'"
+        apply(erule_tac exE, erule_tac exE)
+        apply(rule_tac x = "stp + stpa" in exI, simp)
+        using g3 by simp
+    qed
+  qed
+qed
+
+
+
+locale turing_merge =
+  fixes A :: "tprog" and B :: "tprog" and P1 :: "assert"
+  and P2 :: "assert"
+  and P3 :: "assert"
+  and P4 :: "assert"
+  and Q1:: "assert"
+  and Q2 :: "assert"
+  assumes 
+  A_wf : "tm_wf A"
+  and B_wf : "tm_wf B"
+  and A_halt : "P1 tp \<Longrightarrow> \<exists> stp. let (s, tp') = steps (Suc 0, tp) A stp in s = 0 \<and> Q1 tp'"
+  and B_halt : "P2 tp \<Longrightarrow> \<exists> stp. let (s, tp') = steps (Suc 0, tp) B stp in s = 0 \<and> Q2 tp'"
+  and A_uhalt : "P3 tp \<Longrightarrow> \<not> (\<exists> stp. is_final (steps (Suc 0, tp) A stp))"
+  and B_uhalt: "P4 tp \<Longrightarrow> \<not> (\<exists> stp. is_final (steps (Suc 0, tp) B stp))"
+begin
+
+
+text {*
+  The following lemma tries to derive the Hoare logic rule for sequentially combined TMs.
+  It deals with the situtation when both @{text "A"} and @{text "B"} are terminated.
+*}
+
+
+
+lemma  t_merge_uhalt_tmp:
+  assumes B_uh: "\<forall>stp. \<not> is_final (steps (Suc 0, b, c) B stp)"
+  and merge_ah: "steps (Suc 0, tp) (A |+| B) stpa = (Suc (length A div 2), b, c)" 
+  shows "\<forall> stp. \<not> is_final (steps (Suc 0, tp) (A |+| B) stp)"
+  using B_uh merge_ah
+apply(rule_tac allI)
+apply(case_tac "stp > stpa")
+apply(erule_tac x = "stp - stpa" in allE)
+apply(case_tac "(steps (Suc 0, b, c) B (stp - stpa))", simp)
+proof -
+  fix stp a ba ca 
+  assume h1: "\<not> is_final (a, ba, ca)" "stpa < stp"
+  and h2: "steps (Suc 0, b, c) B (stp - stpa) = (a, ba, ca)"
+  have "steps (Suc 0 + length A div 2, b, c) (A |+| B) (stp - stpa) = 
+      (if a = 0 then 0 else a + length A div 2, ba, ca)"
+    using A_wf B_wf h2
+    by(rule_tac t_merge_snd_eq_steps, auto)
+  moreover have "a > 0" using h1 by(simp add: is_final_def)
+  moreover have "\<exists> stpb. stp = stpa + stpb" 
+    using h1 by(rule_tac x = "stp - stpa" in exI, simp)
+  ultimately show "\<not> is_final (steps (Suc 0, tp) (A |+| B) stp)"
+    using merge_ah
+    by(auto simp: steps_add is_final_def)
+next
+  fix stp
+  assume h: "steps (Suc 0, tp) (A |+| B) stpa = (Suc (length A div 2), b, c)" "\<not> stpa < stp"
+  hence "\<exists> stpb. stpa = stp + stpb" apply(rule_tac x = "stpa - stp" in exI, auto) done
+  thus "\<not> is_final (steps (Suc 0, tp) (A |+| B) stp)"
+    using h
+    apply(auto)
+    apply(cases "steps (Suc 0, tp) (A |+| B) stp", simp add: steps_add is_final_def steps_0)
+    done
+qed
+
+text {*
+  The following lemma deals with the situation when TM @{text "B"} can not terminate.
+  *}
+
+lemma t_merge_uhalt: 
+  assumes aimpb: "Q1 \<mapsto> P4"
+  shows "P1 \<mapsto> \<lambda> tp. \<not> (\<exists> stp. is_final (steps (Suc 0, tp) (A |+| B) stp))"
+proof(simp only: assert_imp_def, rule_tac allI, rule_tac impI)
+  fix tp 
+  assume init_asst: "P1 tp"
+  show "\<not> (\<exists>stp. is_final (steps (Suc 0, tp) (A |+| B) stp))"
+  proof -
+    have "\<exists> stp. let (s, tp') = steps (Suc 0, tp) A stp in s = 0 \<and> Q1 tp'"
+      using A_halt[of tp] init_asst
+      by(simp)
+    from this obtain stpx where "let (s, tp') = steps (Suc 0, tp) A stpx in s = 0 \<and> Q1 tp'" ..
+    thus "?thesis"
+    proof(cases "steps (Suc 0, tp) A stpx", simp, erule_tac conjE)
+      fix a b c
+      assume "Q1 (b, c)"
+        and h3: "steps (Suc 0, tp) A stpx = (0, b, c)"
+      hence h2: "P4 (b, c)"  using aimpb
+        by(simp add: assert_imp_def)
+      have "\<exists> stp. steps (Suc 0, tp) (A |+| B) stp = (Suc (length A div 2), b, c)"
+        using h3 A_wf B_wf
+        apply(rule_tac stp = stpx in t_merge_pre_halt_same, auto)
+        done
+      from this obtain stpa where h4:"steps (Suc 0, tp) (A |+| B) stpa = (Suc (length A div 2), b, c)" ..
+      have " \<not> (\<exists> stp. is_final (steps (Suc 0, b, c) B stp))"
+        using B_uhalt [of "(b, c)"] h2 apply simp
+        done
+      from this and h4 show "\<forall>stp. \<not> is_final (steps (Suc 0, tp) (A |+| B) stp)"
+        by(rule_tac t_merge_uhalt_tmp, auto)
+    qed
+  qed
+qed
+end
+
+end
+




