From Undecidability Require Import TM.Util.TM_facts.
Require Import Undecidability.Shared.Libs.PSL.FiniteTypes.DepPairs EqdepFacts.
Section While.
Variable n : nat.
Variable sig : finType.
Variable F : finType.
Variable pM : pTM sig (option F) n.
Definition While_trans :
(TM.state (projT1 pM)) * Vector.t (option sig) n ->
(TM.state (projT1 pM)) * Vector.t (option sig * move) n :=
fun '(q,s) =>
if halt q
then (start (projT1 pM), nop_action)
else trans (q,s).
Definition WhileTM : TM sig n :=
Build_TM While_trans (start (projT1 pM))
(fun q => halt q && match projT2 pM q with
| Some _ => true
| None => false
end).
Hypothesis (defF : inhabitedC F).
Definition While_part : state (projT1 pM) -> F :=
fun q =>
match projT2 pM q with
| Some y => y
| None => default
end.
Definition While : pTM sig F n :=
(WhileTM; While_part).
Local Arguments loopM {_ _} _ _ _.
Local Arguments halt {_ _} _ _.
Local Arguments step {_ _} _ _.
Lemma step_comp (c : mconfig sig (state (projT1 pM)) n) :
haltConf c = false ->
step (projT1 pM) c = step WhileTM c.
Proof.
intros HHalt. unfold haltConf in HHalt.
destruct c as [q t]. cbn in *.
cbv [step]. cbn. rewrite HHalt. reflexivity.
Qed.
Lemma halt_comp (c : mconfig sig (state (projT1 pM)) n) :
haltConf (M := projT1 pM) c = false ->
haltConf (M := WhileTM) c = false.
Proof.
intros HHalt. cbn in *.
destruct c as [q t]. cbn in *.
apply andb_false_iff. now left.
Qed.
Lemma While_trans_repeat (c : mconfig sig (state WhileTM) n) :
haltConf (M := projT1 pM) c = true ->
projT2 pM (cstate c) = None ->
step WhileTM c = initc (WhileTM) (ctapes c).
Proof.
intros HHalt HRepeat. unfold haltConf in HHalt.
destruct c as [q t]; cbn in *.
unfold step. cbn -[doAct_multi] in *. rewrite HHalt. unfold initc. f_equal. apply doAct_nop.
Qed.
Lemma While_split k (c1 c3 : mconfig sig (state (projT1 pM)) n) :
loopM WhileTM c1 k = Some c3 ->
exists k1 k2 c2,
loopM (projT1 pM) c1 k1 = Some c2 /\
loopM WhileTM c2 k2 = Some c3 /\
k1 + k2 <= k.
Proof.
unfold loopM. intros HLoop.
apply loop_split with (h := haltConf (M := projT1 pM)) in HLoop as (k1&c2&k2&HLoop&HLoop'&Hk).
- exists k1, k2, c2. repeat split; eauto.
apply loop_lift with (lift := id) (f' := step (projT1 pM)) (h' := haltConf (M := projT1 pM)) in HLoop.
+ apply HLoop.
+ auto.
+ apply step_comp.
- apply halt_comp.
Qed.
Lemma While_split_repeat k (c1 c2 : mconfig sig (state WhileTM) n) :
loopM WhileTM c1 k = Some c2 ->
haltConf (M := projT1 pM) c1 = true ->
projT2 pM (cstate c1) = None ->
exists k' : nat,
k = S k' /\
loopM WhileTM (initc WhileTM (ctapes c1)) k' = Some c2.
Proof.
intros HLoop HHalt HRepeat. unfold haltConf in HHalt.
destruct k as [ | k']; cbn in *.
- rewrite HHalt, HRepeat in HLoop. cbn in HLoop. inv HLoop.
- rewrite HHalt, HRepeat in HLoop. cbn in HLoop. exists k'. split. reflexivity.
now rewrite While_trans_repeat in HLoop by auto.
Qed.
Lemma While_split_term k (c1 c2 : mconfig sig (state WhileTM) n) (f : F) :
loopM WhileTM c1 k = Some c2 ->
haltConf (M := projT1 pM) c1 = true ->
projT2 pM (cstate c1) = Some f ->
c2 = c1.
Proof.
intros HLoop HHalt HTerm. unfold loopM in *.
eapply loop_eq_0. 2: apply HLoop. unfold haltConf in *. cbn in *. now rewrite HHalt, HTerm.
Qed.
Lemma While_merge_repeat k1 k2 (c1 c2 c3 : mconfig sig (state WhileTM) n) :
loopM (projT1 pM) c1 k1 = Some c2 ->
(projT2 pM) (cstate c2) = None ->
loopM WhileTM (initc WhileTM (ctapes c2)) k2 = Some c3 ->
loopM WhileTM c1 (k1+(1+k2)) = Some c3.
Proof.
intros HLoop1 HRepeat HLoop2. unfold loopM in *.
eapply loop_lift with (lift := id) (f' := step (WhileTM)) (h' := haltConf (M := projT1 pM)) in HLoop1; cbv [id] in *; cbn; auto; cycle 1.
{ intros. symmetry. now apply step_comp. }
apply loop_merge with (h := haltConf (M := projT1 pM)) (a2 := c2).
- apply halt_comp.
- apply HLoop1.
- cbn [loop plus]. rewrite While_trans_repeat; auto. 2: apply (loop_fulfills HLoop1).
cbn in *. setoid_rewrite (loop_fulfills HLoop1). now rewrite HRepeat.
Qed.
Lemma While_merge_term k1 (c1 c2 : mconfig sig (state WhileTM) n) (f : F) :
loopM (projT1 pM) c1 k1 = Some c2 ->
(projT2 pM) (cstate c2) = Some f ->
loopM WhileTM c1 k1 = Some c2.
Proof.
intros HLoop HTerm. unfold loopM in *.
eapply loop_lift with (lift := id) (f' := step (WhileTM)) (h' := haltConf (M := projT1 pM)) in HLoop; cbv [id] in *; cbn; auto; cycle 1.
{ intros. symmetry. now apply step_comp. }
unfold loopM.
replace k1 with (k1 + 0) by lia.
apply loop_merge with (h := haltConf (M := projT1 pM)) (a2 := c2).
- apply halt_comp.
- apply HLoop.
- cbn in *. setoid_rewrite (loop_fulfills HLoop). rewrite HTerm. cbn. reflexivity.
Qed.
Variable R : pRel sig (option F) n.
Inductive While_Rel : pRel sig F n :=
| While_Rel''_one :
forall tin yout tout, R tin (Some yout, tout) -> While_Rel tin (yout, tout)
| While_Rel''_loop :
forall tin tmid yout tout,
R tin (None, tmid) ->
While_Rel tmid (yout, tout) ->
While_Rel tin (yout, tout).
Lemma While_Realise :
pM ⊨ R -> While ⊨ While_Rel.
Proof.
intros HRel. hnf in HRel; hnf. intros t k; revert t. apply complete_induction with (x := k); clear k; intros k IH. intros tin c3 HLoop.
apply While_split in HLoop as (k1&k2&c2&HLoop1&HLoop2&Hk).
destruct (projT2 pM (cstate c2)) as [ f | ] eqn:E; cbn in *; [ clear IH | ].
- apply While_split_term with (f := f) in HLoop2 as ->; auto. 2: apply (loop_fulfills HLoop1). unfold While_part. rewrite E.
constructor 1. specialize HRel with (1 := HLoop1). now rewrite E in HRel.
- apply While_split_repeat in HLoop2 as (k2'&->&HLoop2); auto. 2: apply (loop_fulfills HLoop1).
specialize IH with (2 := HLoop2); spec_assert IH by lia.
econstructor 2.
+ specialize HRel with (1 := HLoop1). rewrite E in HRel. eassumption.
+ apply IH.
Qed.
Section While_TerminatesIn.
Variable (T T' : Rel (tapes sig n) nat).
Lemma While_TerminatesIn_ind :
pM ⊨ R ->
projT1 pM ↓ T' ->
(forall (tin : tapes sig n) (k : nat),
T tin k ->
exists k1,
T' tin k1 /\
(forall ymid tmid, R tin (Some ymid, tmid) -> k1 <= k) /\
(forall tmid, R tin (None, tmid) -> exists k2, T tmid k2 /\ 1 + k1 + k2 <= k)) ->
WhileTM ↓T.
Proof.
intros Realise_M Term_M Hyp tin i. revert tin. apply complete_induction with (x:=i); clear i; intros i IH tin.
intros (i1&HT1&HT2&HT3) % Hyp. pose proof (Term_M _ _ HT1) as (oconf&Hloop).
specialize (Realise_M _ _ _ Hloop).
destruct (projT2 pM (cstate oconf)) as [ ymid | ] eqn:E1.
- specialize HT2 with (1 := Realise_M).
exists oconf. eapply loop_monotone; eauto. eapply While_merge_term; eauto.
- specialize HT3 with (1 := Realise_M) as (i2&HT3&Hi).
specialize (IH i2 ltac:(lia) _ HT3) as (oconf2&Hloop2).
exists oconf2. apply loop_monotone with (k1 := i1 + (1 + i2)). 2: lia.
eapply While_merge_repeat; eauto.
Qed.
End While_TerminatesIn.
Section While_TerminatesIn_coind.
Variable (T : Rel (tapes sig n) nat).
CoInductive While_T : tRel sig n :=
| While_T_intro tin k k1 :
T tin k1 ->
(forall tmid ymid,
R tin (Some ymid, tmid) -> k1 <= k) ->
(forall tmid,
R tin (None, tmid) ->
exists k2, While_T tmid k2 /\ 1 + k1 + k2 <= k) ->
While_T tin k.
Lemma While_TerminatesIn :
pM ⊨ R ->
projT1 pM ↓ T ->
WhileTM ↓ While_T.
Proof.
intros HRel HTerm. eapply While_TerminatesIn_ind; eauto.
intros tin k' HCoInd. destruct HCoInd as [ t k k1 H1 H2 H3 ]. eauto.
Qed.
End While_TerminatesIn_coind.
End While.
Arguments While : simpl never.
Arguments While {n sig F} pM {defF}.
Notation WHILE := While (only parsing).
Section WhileInduction.
Variable (sig : finType) (n : nat) (F : finType).
Variable R1 : pRel sig (option F) n.
Variable R2 : pRel sig F n.
Lemma WhileInduction :
(forall tin yout tout (HLastStep: R1 tin (Some yout, tout)), R2 tin (yout, tout)) ->
(forall tin tmid tout yout
(HStar : R1 tin (None, tmid)) (HLastStep : R2 tmid (yout, tout)), R2 tin (yout, tout)) ->
While_Rel R1 <<=2 R2.
Proof. intros H1 H2. intros tin tout. induction 1; eauto. Qed.
End WhileInduction.
Section WhileCoInduction.
Variable (sig : finType) (n : nat) (F : finType).
Variable R : pRel sig (option F) n.
Variable T T' : tRel sig n.
Lemma WhileCoInduction :
(forall (tin : tapes sig n) (k : nat) (HT : T tin k),
exists k1,
T' tin k1 /\
forall (ymid : option F) tmid,
R tin (ymid, tmid) ->
match ymid with
| Some _ => k1 <= k
| None => exists k2, T tmid k2 /\ 1 + k1 + k2 <= k
end) ->
T <<=2 While_T R T'.
Proof.
intros. cofix IH. intros tin k HT. specialize H with (1 := HT) as (k1&H1&H2). econstructor; eauto.
- intros tmid ymid HR. specialize (H2 (Some ymid) tmid); cbn in *. auto.
- intros tmid HR. specialize (H2 None tmid) as (k2&H3&H4); eauto.
Qed.
End WhileCoInduction.
Section OtherWhileRel.
Variable (sig : finType) (n : nat) (F : finType).
Variable R : Rel (tapes sig n) (option F * tapes sig n).
Definition While_Rel' : pRel sig F n :=
(star (R |_ None)) ∘ ⋃_y (R |_(Some y)) ||_y.
Goal While_Rel R =2 While_Rel'.
Proof.
unfold While_Rel'. split.
{
apply WhileInduction; intros; cbn in *.
- eexists. split. constructor. exists yout. auto.
- destruct HLastStep as (y&IH1&?&<-&IH2); cbn in *.
eexists. split; eauto. econstructor; eauto.
}
{
intros tin (yout, tout) H. cbn in H. destruct H as (tmid&HStar&HLastStep).
induction HStar as [ tin | tin tmid tmid2 HS1 HS2 IH].
- destruct HLastStep as (?&<-&H). now constructor.
- spec_assert IH by assumption.
destruct HLastStep as (?&<-&H).
econstructor 2.
+ apply HS1.
+ apply IH.
}
Qed.
End OtherWhileRel.
Require Import Undecidability.Shared.Libs.PSL.FiniteTypes.DepPairs EqdepFacts.
Section While.
Variable n : nat.
Variable sig : finType.
Variable F : finType.
Variable pM : pTM sig (option F) n.
Definition While_trans :
(TM.state (projT1 pM)) * Vector.t (option sig) n ->
(TM.state (projT1 pM)) * Vector.t (option sig * move) n :=
fun '(q,s) =>
if halt q
then (start (projT1 pM), nop_action)
else trans (q,s).
Definition WhileTM : TM sig n :=
Build_TM While_trans (start (projT1 pM))
(fun q => halt q && match projT2 pM q with
| Some _ => true
| None => false
end).
Hypothesis (defF : inhabitedC F).
Definition While_part : state (projT1 pM) -> F :=
fun q =>
match projT2 pM q with
| Some y => y
| None => default
end.
Definition While : pTM sig F n :=
(WhileTM; While_part).
Local Arguments loopM {_ _} _ _ _.
Local Arguments halt {_ _} _ _.
Local Arguments step {_ _} _ _.
Lemma step_comp (c : mconfig sig (state (projT1 pM)) n) :
haltConf c = false ->
step (projT1 pM) c = step WhileTM c.
Proof.
intros HHalt. unfold haltConf in HHalt.
destruct c as [q t]. cbn in *.
cbv [step]. cbn. rewrite HHalt. reflexivity.
Qed.
Lemma halt_comp (c : mconfig sig (state (projT1 pM)) n) :
haltConf (M := projT1 pM) c = false ->
haltConf (M := WhileTM) c = false.
Proof.
intros HHalt. cbn in *.
destruct c as [q t]. cbn in *.
apply andb_false_iff. now left.
Qed.
Lemma While_trans_repeat (c : mconfig sig (state WhileTM) n) :
haltConf (M := projT1 pM) c = true ->
projT2 pM (cstate c) = None ->
step WhileTM c = initc (WhileTM) (ctapes c).
Proof.
intros HHalt HRepeat. unfold haltConf in HHalt.
destruct c as [q t]; cbn in *.
unfold step. cbn -[doAct_multi] in *. rewrite HHalt. unfold initc. f_equal. apply doAct_nop.
Qed.
Lemma While_split k (c1 c3 : mconfig sig (state (projT1 pM)) n) :
loopM WhileTM c1 k = Some c3 ->
exists k1 k2 c2,
loopM (projT1 pM) c1 k1 = Some c2 /\
loopM WhileTM c2 k2 = Some c3 /\
k1 + k2 <= k.
Proof.
unfold loopM. intros HLoop.
apply loop_split with (h := haltConf (M := projT1 pM)) in HLoop as (k1&c2&k2&HLoop&HLoop'&Hk).
- exists k1, k2, c2. repeat split; eauto.
apply loop_lift with (lift := id) (f' := step (projT1 pM)) (h' := haltConf (M := projT1 pM)) in HLoop.
+ apply HLoop.
+ auto.
+ apply step_comp.
- apply halt_comp.
Qed.
Lemma While_split_repeat k (c1 c2 : mconfig sig (state WhileTM) n) :
loopM WhileTM c1 k = Some c2 ->
haltConf (M := projT1 pM) c1 = true ->
projT2 pM (cstate c1) = None ->
exists k' : nat,
k = S k' /\
loopM WhileTM (initc WhileTM (ctapes c1)) k' = Some c2.
Proof.
intros HLoop HHalt HRepeat. unfold haltConf in HHalt.
destruct k as [ | k']; cbn in *.
- rewrite HHalt, HRepeat in HLoop. cbn in HLoop. inv HLoop.
- rewrite HHalt, HRepeat in HLoop. cbn in HLoop. exists k'. split. reflexivity.
now rewrite While_trans_repeat in HLoop by auto.
Qed.
Lemma While_split_term k (c1 c2 : mconfig sig (state WhileTM) n) (f : F) :
loopM WhileTM c1 k = Some c2 ->
haltConf (M := projT1 pM) c1 = true ->
projT2 pM (cstate c1) = Some f ->
c2 = c1.
Proof.
intros HLoop HHalt HTerm. unfold loopM in *.
eapply loop_eq_0. 2: apply HLoop. unfold haltConf in *. cbn in *. now rewrite HHalt, HTerm.
Qed.
Lemma While_merge_repeat k1 k2 (c1 c2 c3 : mconfig sig (state WhileTM) n) :
loopM (projT1 pM) c1 k1 = Some c2 ->
(projT2 pM) (cstate c2) = None ->
loopM WhileTM (initc WhileTM (ctapes c2)) k2 = Some c3 ->
loopM WhileTM c1 (k1+(1+k2)) = Some c3.
Proof.
intros HLoop1 HRepeat HLoop2. unfold loopM in *.
eapply loop_lift with (lift := id) (f' := step (WhileTM)) (h' := haltConf (M := projT1 pM)) in HLoop1; cbv [id] in *; cbn; auto; cycle 1.
{ intros. symmetry. now apply step_comp. }
apply loop_merge with (h := haltConf (M := projT1 pM)) (a2 := c2).
- apply halt_comp.
- apply HLoop1.
- cbn [loop plus]. rewrite While_trans_repeat; auto. 2: apply (loop_fulfills HLoop1).
cbn in *. setoid_rewrite (loop_fulfills HLoop1). now rewrite HRepeat.
Qed.
Lemma While_merge_term k1 (c1 c2 : mconfig sig (state WhileTM) n) (f : F) :
loopM (projT1 pM) c1 k1 = Some c2 ->
(projT2 pM) (cstate c2) = Some f ->
loopM WhileTM c1 k1 = Some c2.
Proof.
intros HLoop HTerm. unfold loopM in *.
eapply loop_lift with (lift := id) (f' := step (WhileTM)) (h' := haltConf (M := projT1 pM)) in HLoop; cbv [id] in *; cbn; auto; cycle 1.
{ intros. symmetry. now apply step_comp. }
unfold loopM.
replace k1 with (k1 + 0) by lia.
apply loop_merge with (h := haltConf (M := projT1 pM)) (a2 := c2).
- apply halt_comp.
- apply HLoop.
- cbn in *. setoid_rewrite (loop_fulfills HLoop). rewrite HTerm. cbn. reflexivity.
Qed.
Variable R : pRel sig (option F) n.
Inductive While_Rel : pRel sig F n :=
| While_Rel''_one :
forall tin yout tout, R tin (Some yout, tout) -> While_Rel tin (yout, tout)
| While_Rel''_loop :
forall tin tmid yout tout,
R tin (None, tmid) ->
While_Rel tmid (yout, tout) ->
While_Rel tin (yout, tout).
Lemma While_Realise :
pM ⊨ R -> While ⊨ While_Rel.
Proof.
intros HRel. hnf in HRel; hnf. intros t k; revert t. apply complete_induction with (x := k); clear k; intros k IH. intros tin c3 HLoop.
apply While_split in HLoop as (k1&k2&c2&HLoop1&HLoop2&Hk).
destruct (projT2 pM (cstate c2)) as [ f | ] eqn:E; cbn in *; [ clear IH | ].
- apply While_split_term with (f := f) in HLoop2 as ->; auto. 2: apply (loop_fulfills HLoop1). unfold While_part. rewrite E.
constructor 1. specialize HRel with (1 := HLoop1). now rewrite E in HRel.
- apply While_split_repeat in HLoop2 as (k2'&->&HLoop2); auto. 2: apply (loop_fulfills HLoop1).
specialize IH with (2 := HLoop2); spec_assert IH by lia.
econstructor 2.
+ specialize HRel with (1 := HLoop1). rewrite E in HRel. eassumption.
+ apply IH.
Qed.
Section While_TerminatesIn.
Variable (T T' : Rel (tapes sig n) nat).
Lemma While_TerminatesIn_ind :
pM ⊨ R ->
projT1 pM ↓ T' ->
(forall (tin : tapes sig n) (k : nat),
T tin k ->
exists k1,
T' tin k1 /\
(forall ymid tmid, R tin (Some ymid, tmid) -> k1 <= k) /\
(forall tmid, R tin (None, tmid) -> exists k2, T tmid k2 /\ 1 + k1 + k2 <= k)) ->
WhileTM ↓T.
Proof.
intros Realise_M Term_M Hyp tin i. revert tin. apply complete_induction with (x:=i); clear i; intros i IH tin.
intros (i1&HT1&HT2&HT3) % Hyp. pose proof (Term_M _ _ HT1) as (oconf&Hloop).
specialize (Realise_M _ _ _ Hloop).
destruct (projT2 pM (cstate oconf)) as [ ymid | ] eqn:E1.
- specialize HT2 with (1 := Realise_M).
exists oconf. eapply loop_monotone; eauto. eapply While_merge_term; eauto.
- specialize HT3 with (1 := Realise_M) as (i2&HT3&Hi).
specialize (IH i2 ltac:(lia) _ HT3) as (oconf2&Hloop2).
exists oconf2. apply loop_monotone with (k1 := i1 + (1 + i2)). 2: lia.
eapply While_merge_repeat; eauto.
Qed.
End While_TerminatesIn.
Section While_TerminatesIn_coind.
Variable (T : Rel (tapes sig n) nat).
CoInductive While_T : tRel sig n :=
| While_T_intro tin k k1 :
T tin k1 ->
(forall tmid ymid,
R tin (Some ymid, tmid) -> k1 <= k) ->
(forall tmid,
R tin (None, tmid) ->
exists k2, While_T tmid k2 /\ 1 + k1 + k2 <= k) ->
While_T tin k.
Lemma While_TerminatesIn :
pM ⊨ R ->
projT1 pM ↓ T ->
WhileTM ↓ While_T.
Proof.
intros HRel HTerm. eapply While_TerminatesIn_ind; eauto.
intros tin k' HCoInd. destruct HCoInd as [ t k k1 H1 H2 H3 ]. eauto.
Qed.
End While_TerminatesIn_coind.
End While.
Arguments While : simpl never.
Arguments While {n sig F} pM {defF}.
Notation WHILE := While (only parsing).
Section WhileInduction.
Variable (sig : finType) (n : nat) (F : finType).
Variable R1 : pRel sig (option F) n.
Variable R2 : pRel sig F n.
Lemma WhileInduction :
(forall tin yout tout (HLastStep: R1 tin (Some yout, tout)), R2 tin (yout, tout)) ->
(forall tin tmid tout yout
(HStar : R1 tin (None, tmid)) (HLastStep : R2 tmid (yout, tout)), R2 tin (yout, tout)) ->
While_Rel R1 <<=2 R2.
Proof. intros H1 H2. intros tin tout. induction 1; eauto. Qed.
End WhileInduction.
Section WhileCoInduction.
Variable (sig : finType) (n : nat) (F : finType).
Variable R : pRel sig (option F) n.
Variable T T' : tRel sig n.
Lemma WhileCoInduction :
(forall (tin : tapes sig n) (k : nat) (HT : T tin k),
exists k1,
T' tin k1 /\
forall (ymid : option F) tmid,
R tin (ymid, tmid) ->
match ymid with
| Some _ => k1 <= k
| None => exists k2, T tmid k2 /\ 1 + k1 + k2 <= k
end) ->
T <<=2 While_T R T'.
Proof.
intros. cofix IH. intros tin k HT. specialize H with (1 := HT) as (k1&H1&H2). econstructor; eauto.
- intros tmid ymid HR. specialize (H2 (Some ymid) tmid); cbn in *. auto.
- intros tmid HR. specialize (H2 None tmid) as (k2&H3&H4); eauto.
Qed.
End WhileCoInduction.
Section OtherWhileRel.
Variable (sig : finType) (n : nat) (F : finType).
Variable R : Rel (tapes sig n) (option F * tapes sig n).
Definition While_Rel' : pRel sig F n :=
(star (R |_ None)) ∘ ⋃_y (R |_(Some y)) ||_y.
Goal While_Rel R =2 While_Rel'.
Proof.
unfold While_Rel'. split.
{
apply WhileInduction; intros; cbn in *.
- eexists. split. constructor. exists yout. auto.
- destruct HLastStep as (y&IH1&?&<-&IH2); cbn in *.
eexists. split; eauto. econstructor; eauto.
}
{
intros tin (yout, tout) H. cbn in H. destruct H as (tmid&HStar&HLastStep).
induction HStar as [ tin | tin tmid tmid2 HS1 HS2 IH].
- destruct HLastStep as (?&<-&H). now constructor.
- spec_assert IH by assumption.
destruct HLastStep as (?&<-&H).
econstructor 2.
+ apply HS1.
+ apply IH.
}
Qed.
End OtherWhileRel.