
theory Re1
  imports "Main" 
begin

section {* Sequential Composition of Sets *}

definition
  Sequ :: "string set \<Rightarrow> string set \<Rightarrow> string set" ("_ ;; _" [100,100] 100)
where 
  "A ;; B = {s1 @ s2 | s1 s2. s1 \<in> A \<and> s2 \<in> B}"

text {* Two Simple Properties about Sequential Composition *}

lemma seq_empty [simp]:
  shows "A ;; {[]} = A"
  and   "{[]} ;; A = A"
by (simp_all add: Sequ_def)

lemma seq_null [simp]:
  shows "A ;; {} = {}"
  and   "{} ;; A = {}"
by (simp_all add: Sequ_def)

section {* Regular Expressions *}

datatype rexp =
  NULL
| EMPTY
| CHAR char
| SEQ rexp rexp
| ALT rexp rexp

section {* Semantics of Regular Expressions *}
 
fun
  L :: "rexp \<Rightarrow> string set"
where
  "L (NULL) = {}"
| "L (EMPTY) = {[]}"
| "L (CHAR c) = {[c]}"
| "L (SEQ r1 r2) = (L r1) ;; (L r2)"
| "L (ALT r1 r2) = (L r1) \<union> (L r2)"


section {* Values *}

datatype val = 
  Void
| Char char
| Seq val val
| Right val
| Left val

section {* Relation between values and regular expressions *}

inductive Prf :: "val \<Rightarrow> rexp \<Rightarrow> bool" ("\<turnstile> _ : _" [100, 100] 100)
where
 "\<lbrakk>\<turnstile> v1 : r1; \<turnstile> v2 : r2\<rbrakk> \<Longrightarrow> \<turnstile> Seq v1 v2 : SEQ r1 r2"
| "\<turnstile> v1 : r1 \<Longrightarrow> \<turnstile> Left v1 : ALT r1 r2"
| "\<turnstile> v2 : r2 \<Longrightarrow> \<turnstile> Right v2 : ALT r1 r2"
| "\<turnstile> Void : EMPTY"
| "\<turnstile> Char c : CHAR c"

section {* The string behind a value *}

fun flat :: "val \<Rightarrow> string"
where
  "flat(Void) = []"
| "flat(Char c) = [c]"
| "flat(Left v) = flat(v)"
| "flat(Right v) = flat(v)"
| "flat(Seq v1 v2) = flat(v1) @ flat(v2)"


lemma Prf_flat_L:
  assumes "\<turnstile> v : r" shows "flat v \<in> L r"
using assms
apply(induct)
apply(auto simp add: Sequ_def)
done

lemma L_flat_Prf:
  "L(r) = {flat v | v. \<turnstile> v : r}"
apply(induct r)
apply(auto dest: Prf_flat_L simp add: Sequ_def)
apply (metis Prf.intros(4) flat.simps(1))
apply (metis Prf.intros(5) flat.simps(2))
apply (metis Prf.intros(1) flat.simps(5))
apply (metis Prf.intros(2) flat.simps(3))
apply (metis Prf.intros(3) flat.simps(4))
apply(erule Prf.cases)
apply(auto)
done

section {* Ordering of values *}

inductive ValOrd :: "val \<Rightarrow> rexp \<Rightarrow> val \<Rightarrow> bool" ("_ \<succ>_ _" [100, 100, 100] 100)
where
  "\<lbrakk>v1 = v1'; v2 \<succ>r2 v2'\<rbrakk> \<Longrightarrow> (Seq v1 v2) \<succ>(SEQ r1 r2) (Seq v1' v2')" 
| "v1  \<succ>r1 v1' \<Longrightarrow> (Seq v1 v2) \<succ>(SEQ r1 r2) (Seq v1' v2')" 
| "length (flat v1) \<ge> length (flat v2) \<Longrightarrow> (Left v1) \<succ>(ALT r1 r2) (Right v2)"
| "length (flat v2) > length (flat v1) \<Longrightarrow> (Right v2) \<succ>(ALT r1 r2) (Left v1)"
| "v2 \<succ>r2 v2' \<Longrightarrow> (Right v2) \<succ>(ALT r1 r2) (Right v2')"
| "v1 \<succ>r1 v1' \<Longrightarrow> (Left v1) \<succ>(ALT r1 r2) (Left v1')"
| "Void \<succ>EMPTY Void"
| "(Char c) \<succ>(CHAR c) (Char c)"

(*
lemma
  assumes "r = SEQ (ALT EMPTY EMPTY) (ALT EMPTY (CHAR c))"
  shows "(Seq (Left Void) (Right (Char c))) \<succ>r (Seq (Left Void) (Left Void))"
using assms
apply(simp)
apply(rule ValOrd.intros)
apply(rule ValOrd.intros)
apply(rule ValOrd.intros)
apply(rule ValOrd.intros)
apply(simp)
done
*)

section {* Posix definition *}

definition POSIX :: "val \<Rightarrow> rexp \<Rightarrow> bool" 
where
  "POSIX v r \<equiv> (\<forall>v'. (\<turnstile> v' : r \<and> flat v = flat v') \<longrightarrow> v \<succ>r v')"

(*
an alternative definition: might cause problems
with theorem mkeps_POSIX
*)

definition POSIX2 :: "val \<Rightarrow> rexp \<Rightarrow> bool" 
where
  "POSIX2 v r \<equiv> \<turnstile> v : r \<and> (\<forall>v'. \<turnstile> v' : r \<longrightarrow> v \<succ>r v')"

definition POSIX3 :: "val \<Rightarrow> rexp \<Rightarrow> bool" 
where
  "POSIX3 v r \<equiv> \<turnstile> v : r \<and> (\<forall>v'. (\<turnstile> v' : r \<and> length (flat v') \<le> length(flat v)) \<longrightarrow> v \<succ>r v')"


(*
lemma POSIX_SEQ:
  assumes "POSIX (Seq v1 v2) (SEQ r1 r2)" "\<turnstile> v1 : r1" "\<turnstile> v2 : r2"
  shows "POSIX v1 r1 \<and> POSIX v2 r2"
using assms
unfolding POSIX_def
apply(auto)
apply(drule_tac x="Seq v' v2" in spec)
apply(simp)
apply (smt Prf.intros(1) ValOrd.simps assms(3) rexp.inject(2) val.distinct(15) val.distinct(17) val.distinct(3) val.distinct(9) val.inject(2))
apply(drule_tac x="Seq v1 v'" in spec)
apply(simp)
by (smt Prf.intros(1) ValOrd.simps rexp.inject(2) val.distinct(15) val.distinct(17) val.distinct(3) val.distinct(9) val.inject(2))
*)

(*
lemma POSIX_SEQ_I:
  assumes "POSIX v1 r1" "POSIX v2 r2" 
  shows "POSIX (Seq v1 v2) (SEQ r1 r2)" 
using assms
unfolding POSIX_def
apply(auto)
apply(rotate_tac 2)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(rule ValOrd.intros)

apply(auto)
done
*)




lemma POSIX_ALT2:
  assumes "POSIX (Left v1) (ALT r1 r2)"
  shows "POSIX v1 r1"
using assms
unfolding POSIX_def
apply(auto)
apply(drule_tac x="Left v'" in spec)
apply(simp)
apply(drule mp)
apply(rule Prf.intros)
apply(auto)
apply(erule ValOrd.cases)
apply(simp_all)
done

lemma POSIX2_ALT:
  assumes "POSIX2 (Left v1) (ALT r1 r2)"
  shows "POSIX2 v1 r1"
using assms
unfolding POSIX2_def
apply(auto)
oops

lemma POSIX_ALT:
  assumes "POSIX (Left v1) (ALT r1 r2)"
  shows "POSIX v1 r1"
using assms
unfolding POSIX_def
apply(auto)
apply(drule_tac x="Left v'" in spec)
apply(simp)
apply(drule mp)
apply(rule Prf.intros)
apply(auto)
apply(erule ValOrd.cases)
apply(simp_all)
done

lemma POSIX2_ALT:
  assumes "POSIX2 (Left v1) (ALT r1 r2)"
  shows "POSIX2 v1 r1"
using assms
apply(simp add: POSIX2_def)
apply(auto)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(drule_tac x="Left v'" in spec)
apply(drule mp)
apply(rule Prf.intros)
apply(auto)
apply(erule ValOrd.cases)
apply(simp_all)
done


lemma POSIX_ALT1a:
  assumes "POSIX (Right v2) (ALT r1 r2)"
  shows "POSIX v2 r2"
using assms
unfolding POSIX_def
apply(auto)
apply(drule_tac x="Right v'" in spec)
apply(simp)
apply(drule mp)
apply(rule Prf.intros)
apply(auto)
apply(erule ValOrd.cases)
apply(simp_all)
done

lemma POSIX2_ALT1a:
  assumes "POSIX2 (Right v2) (ALT r1 r2)"
  shows "POSIX2 v2 r2"
using assms
unfolding POSIX2_def
apply(auto)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(drule_tac x="Right v'" in spec)
apply(drule mp)
apply(rule Prf.intros)
apply(auto)
apply(erule ValOrd.cases)
apply(simp_all)
done


lemma POSIX_ALT1b:
  assumes "POSIX (Right v2) (ALT r1 r2)"
  shows "(\<forall>v'. (\<turnstile> v' : r2 \<and> flat v' = flat v2) \<longrightarrow> v2 \<succ>r2 v')"
using assms
apply(drule_tac POSIX_ALT1a)
unfolding POSIX_def
apply(auto)
done

lemma POSIX_ALT_I1:
  assumes "POSIX v1 r1" 
  shows "POSIX (Left v1) (ALT r1 r2)"
using assms
unfolding POSIX_def
apply(auto)
apply(rotate_tac 3)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply(rule ValOrd.intros)
apply(auto)
apply(rule ValOrd.intros)
by simp

lemma POSIX2_ALT_I1:
  assumes "POSIX2 v1 r1" 
  shows "POSIX2 (Left v1) (ALT r1 r2)"
using assms
unfolding POSIX2_def
apply(auto)
apply(rule Prf.intros)
apply(simp)
apply(rotate_tac 2)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply(rule ValOrd.intros)
apply(auto)
apply(rule ValOrd.intros)
oops

lemma POSIX_ALT_I2:
  assumes "POSIX v2 r2" "\<forall>v'. \<turnstile> v' : r1 \<longrightarrow> length (flat v2) > length (flat v')"
  shows "POSIX (Right v2) (ALT r1 r2)"
using assms
unfolding POSIX_def
apply(auto)
apply(rotate_tac 3)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply(rule ValOrd.intros)
apply metis
done


section {* The ordering is reflexive *}

lemma ValOrd_refl:
  assumes "\<turnstile> v : r"
  shows "v \<succ>r v"
using assms
apply(induct)
apply(auto intro: ValOrd.intros)
done


section {* The Matcher *}

fun
 nullable :: "rexp \<Rightarrow> bool"
where
  "nullable (NULL) = False"
| "nullable (EMPTY) = True"
| "nullable (CHAR c) = False"
| "nullable (ALT r1 r2) = (nullable r1 \<or> nullable r2)"
| "nullable (SEQ r1 r2) = (nullable r1 \<and> nullable r2)"

lemma nullable_correctness:
  shows "nullable r  \<longleftrightarrow> [] \<in> (L r)"
apply (induct r) 
apply(auto simp add: Sequ_def) 
done

fun mkeps :: "rexp \<Rightarrow> val"
where
  "mkeps(EMPTY) = Void"
| "mkeps(SEQ r1 r2) = Seq (mkeps r1) (mkeps r2)"
| "mkeps(ALT r1 r2) = (if nullable(r1) then Left (mkeps r1) else Right (mkeps r2))"

lemma mkeps_nullable:
  assumes "nullable(r)" shows "\<turnstile> mkeps r : r"
using assms
apply(induct rule: nullable.induct)
apply(auto intro: Prf.intros)
done

lemma mkeps_flat:
  assumes "nullable(r)" shows "flat (mkeps r) = []"
using assms
apply(induct rule: nullable.induct)
apply(auto)
done

text {*
  The value mkeps returns is always the correct POSIX
  value.
*}

lemma mkeps_POSIX2:
  assumes "nullable r"
  shows "POSIX2 (mkeps r) r"
using assms
apply(induct r)
apply(auto)[1]
apply(simp add: POSIX2_def)
oops

lemma mkeps_POSIX:
  assumes "nullable r"
  shows "POSIX (mkeps r) r"
using assms
apply(induct r)
apply(auto)[1]
apply(simp add: POSIX_def)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply (metis ValOrd.intros)
apply(simp add: POSIX_def)
apply(auto)[1]
apply(simp add: POSIX_def)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply (simp add: ValOrd.intros(2) mkeps_flat)
apply(simp add: POSIX_def)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply (simp add: ValOrd.intros(6))
apply (simp add: ValOrd.intros(3))
apply(simp add: POSIX_def)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply (simp add: ValOrd.intros(6))
apply (simp add: ValOrd.intros(3))
apply(simp add: POSIX_def)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)
apply (metis Prf_flat_L mkeps_flat nullable_correctness)
by (simp add: ValOrd.intros(5))


lemma mkeps_POSIX2:
  assumes "nullable r"
  shows "POSIX2 (mkeps r) r"
using assms
apply(induct r)
apply(simp)
apply(simp)
apply(simp add: POSIX2_def)
apply(rule conjI)
apply(rule Prf.intros)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(rule ValOrd.intros)
apply(simp)
apply(simp)
apply(simp add: POSIX2_def)
apply(rule conjI)
apply(rule Prf.intros)
apply(simp add: mkeps_nullable)
apply(simp add: mkeps_nullable)
apply(auto)[1]
apply(rotate_tac 6)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(rule ValOrd.intros(2))
apply(simp)
apply(simp only: nullable.simps)
apply(erule disjE)
apply(simp)
thm POSIX2_ALT1a
apply(rule POSIX2_ALT)
apply(simp add: POSIX2_def)
apply(rule conjI)
apply(rule Prf.intros)
apply(simp add: mkeps_nullable)
oops


section {* Derivatives *}

fun
 der :: "char \<Rightarrow> rexp \<Rightarrow> rexp"
where
  "der c (NULL) = NULL"
| "der c (EMPTY) = NULL"
| "der c (CHAR c') = (if c = c' then EMPTY else NULL)"
| "der c (ALT r1 r2) = ALT (der c r1) (der c r2)"
| "der c (SEQ r1 r2) = 
     (if nullable r1
      then ALT (SEQ (der c r1) r2) (der c r2)
      else SEQ (der c r1) r2)"

fun 
 ders :: "string \<Rightarrow> rexp \<Rightarrow> rexp"
where
  "ders [] r = r"
| "ders (c # s) r = ders s (der c r)"

section {* Injection function *}

fun injval :: "rexp \<Rightarrow> char \<Rightarrow> val \<Rightarrow> val"
where
  "injval (CHAR d) c Void = Char d"
| "injval (ALT r1 r2) c (Left v1) = Left(injval r1 c v1)"
| "injval (ALT r1 r2) c (Right v2) = Right(injval r2 c v2)"
| "injval (SEQ r1 r2) c (Seq v1 v2) = Seq (injval r1 c v1) v2"
| "injval (SEQ r1 r2) c (Left (Seq v1 v2)) = Seq (injval r1 c v1) v2"
| "injval (SEQ r1 r2) c (Right v2) = Seq (mkeps r1) (injval r2 c v2)"

section {* Projection function *}

fun projval :: "rexp \<Rightarrow> char \<Rightarrow> val \<Rightarrow> val"
where
  "projval (CHAR d) c _ = Void"
| "projval (ALT r1 r2) c (Left v1) = Left(projval r1 c v1)"
| "projval (ALT r1 r2) c (Right v2) = Right(projval r2 c v2)"
| "projval (SEQ r1 r2) c (Seq v1 v2) = 
     (if flat v1 = [] then Right(projval r2 c v2) 
      else if nullable r1 then Left (Seq (projval r1 c v1) v2)
                          else Seq (projval r1 c v1) v2)"

text {*
  Injection value is related to r
*}

lemma v3:
  assumes "\<turnstile> v : der c r" shows "\<turnstile> (injval r c v) : r"
using assms
apply(induct arbitrary: v rule: der.induct)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(case_tac "c = c'")
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply (metis Prf.intros(5))
apply(erule Prf.cases)
apply(simp_all)[5]
apply(erule Prf.cases)
apply(simp_all)[5]
apply (metis Prf.intros(2))
apply (metis Prf.intros(3))
apply(simp)
apply(case_tac "nullable r1")
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply (metis Prf.intros(1))
apply(auto)[1]
apply (metis Prf.intros(1) mkeps_nullable)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(rule Prf.intros)
apply(auto)[2]
done

text {*
  The string behin the injection value is an added c
*}

lemma v4:
  assumes "\<turnstile> v : der c r" shows "flat (injval r c v) = c # (flat v)"
using assms
apply(induct arbitrary: v rule: der.induct)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(case_tac "c = c'")
apply(simp)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(case_tac "nullable r1")
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply (metis mkeps_flat)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
done

text {*
  Injection followed by projection is the identity.
*}

lemma proj_inj_id:
  assumes "\<turnstile> v : der c r" 
  shows "projval r c (injval r c v) = v"
using assms
apply(induct r arbitrary: c v rule: rexp.induct)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(case_tac "c = char")
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
defer
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(case_tac "nullable rexp1")
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply (metis list.distinct(1) v4)
apply(auto)[1]
apply (metis mkeps_flat)
apply(auto)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(auto)[1]
apply(simp add: v4)
done

lemma "\<exists>v. POSIX v r"
apply(induct r)
apply(rule exI)
apply(simp add: POSIX_def)
apply (metis (full_types) Prf_flat_L der.simps(1) der.simps(2) der.simps(3) flat.simps(1) nullable.simps(1) nullable_correctness proj_inj_id projval.simps(1) v3 v4)
apply(rule_tac x = "Void" in exI)
apply(simp add: POSIX_def)
apply (metis POSIX_def flat.simps(1) mkeps.simps(1) mkeps_POSIX nullable.simps(2))
apply(rule_tac x = "Char char" in exI)
apply(simp add: POSIX_def)
apply(auto) [1]
apply(erule Prf.cases)
apply(simp_all) [5]
apply (metis ValOrd.intros(8))
defer
apply(auto)
apply (metis POSIX_ALT_I1)
(* maybe it is too early to instantiate this existential quantifier *)
(* potentially this is the wrong POSIX value *)
apply(case_tac "r1 = NULL")
apply(simp add: POSIX_def)
apply(auto)[1]
apply (metis L.simps(1) L.simps(4) Prf_flat_L mkeps_flat nullable.simps(1) nullable.simps(2) nullable_correctness seq_null(2))
apply(case_tac "r1 = EMPTY")
apply(rule_tac x = "Seq Void va" in exI )
apply(simp (no_asm) add: POSIX_def)
apply(auto)
apply(erule Prf.cases)
apply(simp_all)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)
apply(rule ValOrd.intros(2))
apply(rule ValOrd.intros)
apply(case_tac "\<exists>c. r1 = CHAR c")
apply(auto)
apply(rule_tac x = "Seq (Char c) va" in exI )
apply(simp (no_asm) add: POSIX_def)
apply(auto)
apply(erule Prf.cases)
apply(simp_all)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)
apply(auto)[1]
apply(rule ValOrd.intros(2))
apply(rule ValOrd.intros)
apply(case_tac "\<exists>r1a r1b. r1 = ALT r1a r1b")
apply(auto)
apply(rule_tac x = "Seq () va" in exI )
apply(simp (no_asm) add: POSIX_def)
apply(auto)
apply(erule Prf.cases)
apply(simp_all)
apply(auto)[1]
apply(erule Prf.cases)
apply(simp_all)
apply(auto)[1]
apply(rule ValOrd.intros(2))
apply(rule ValOrd.intros)

apply(case_tac "v \<succ>r1a v1")
apply (metis ValOrd.intros(2))
apply(simp add: POSIX_def)
apply(case_tac "flat v = flat v1")
apply(auto)[1]
apply(simp only: append_eq_append_conv2)
apply(auto)
thm append_eq_append_conv2

text {* 

  HERE: Crucial lemma that does not go through in the sequence case. 

*}
lemma v5:
  assumes "\<turnstile> v : der c r" "POSIX v (der c r)"
  shows "POSIX (injval r c v) r"
using assms
apply(induct arbitrary: v rule: der.induct)
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(erule Prf.cases)
apply(simp_all)[5]
apply(simp)
apply(case_tac "c = c'")
apply(auto simp add: POSIX_def)[1]
apply(erule Prf.cases)
apply(simp_all)[5]
apply(erule Prf.cases)
apply(simp_all)[5]
using ValOrd.simps apply blast
apply(auto)
apply(erule Prf.cases)
apply(simp_all)[5]
(* base cases done *)
(* ALT case *)
apply(erule Prf.cases)
apply(simp_all)[5]
using POSIX_ALT POSIX_ALT_I1 apply blast
apply(clarify)
apply(subgoal_tac "POSIX v2 (der c r2)")
prefer 2
apply(auto simp add: POSIX_def)[1]
apply (metis POSIX_ALT1a POSIX_def flat.simps(4))
apply(rotate_tac 1)
apply(drule_tac x="v2" in meta_spec)
apply(simp)
apply(subgoal_tac "\<turnstile> Right (injval r2 c v2) : (ALT r1 r2)")
prefer 2
apply (metis Prf.intros(3) v3)
apply(rule ccontr)
apply(auto simp add: POSIX_def)[1]

apply(rule allI)
apply(rule impI)
apply(erule conjE)
thm POSIX_ALT_I2
apply(frule POSIX_ALT1a)
apply(drule POSIX_ALT1b)
apply(rule POSIX_ALT_I2)
apply auto[1]
apply(subst v4)
apply(auto)[2]
apply(rotate_tac 1)
apply(drule_tac x="v2" in meta_spec)
apply(simp)
apply(subst (asm) (4) POSIX_def)
apply(subst (asm) v4)
apply(auto)[2]
(* stuck in the ALT case *)
