From: Andrea Asperti <andrea.asperti@unibo.it>
Date: Fri, 9 Nov 2012 17:57:33 +0000 (+0000)
Subject: if_multi.ma
X-Git-Tag: make_still_working~1480
X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=commitdiff_plain;h=bd3b4677ff8a1cb02fe4745b89e83c77b2dd5287;p=helm.git

if_multi.ma
---

diff --git a/matita/matita/lib/turing/if_multi.ma b/matita/matita/lib/turing/if_multi.ma
new file mode 100644
index 000000000..71d85d4cb
--- /dev/null
+++ b/matita/matita/lib/turing/if_multi.ma
@@ -0,0 +1,455 @@
+(*
+    ||M||  This file is part of HELM, an Hypertextual, Electronic   
+    ||A||  Library of Mathematics, developed at the Computer Science 
+    ||T||  Department of the University of Bologna, Italy.           
+    ||I||                                                            
+    ||T||  
+    ||A||  
+    \   /  This file is distributed under the terms of the       
+     \ /   GNU General Public License Version 2   
+      V_____________________________________________________________*)
+
+include "turing/turing.ma".
+
+(**************************** single final machine ****************************)
+
+definition single_finalTM ≝ 
+  λsig,n.λM:mTM sig n.seq ?? M (nop ??).
+
+lemma sem_single_final: ∀sig,n.∀M: mTM sig n.∀R.
+  M ⊨ R → single_finalTM sig n M ⊨ R.
+#sig #n #M #R #HR #intape 
+cases (sem_seq ?????? HR (sem_nop …) intape)
+#k * #outc * #Hloop * #ta * #Hta whd in ⊢ (%→?); #Houtc
+@(ex_intro ?? k) @(ex_intro ?? outc) %  [ @Hloop | >Houtc // ]
+qed.
+
+lemma single_final: ∀sig,n.∀M: mTM sig n.∀q1,q2.
+  halt ?? (single_finalTM sig n M) q1 = true 
+    →  halt ?? (single_finalTM sig n M) q2 = true → q1=q2.
+#sig #n #M * 
+  [#q1M #q2 whd in match (halt ????); #H destruct
+  |#q1nop *
+    [#q2M #_ whd in match (halt ????); #H destruct
+    |#q2nop #_ #_ @eq_f normalize @nop_single_state
+    ]
+  ]
+qed.
+  
+(******************************** if machine **********************************)
+
+definition if_trans ≝ λsig,n. λM1,M2,M3 : mTM sig n. λq:states sig n M1.
+λp. let 〈s,a〉 ≝ p in
+  match s with 
+  [ inl s1 ⇒ 
+      if halt sig n M1 s1 then
+        if s1==q then 〈inr … (inl … (start sig n M2)), null_action ??〉
+        else 〈inr … (inr … (start sig n M3)), null_action ??〉
+      else let 〈news1,m〉 ≝ trans sig n M1 〈s1,a〉 in
+       〈inl … news1,m〉
+  | inr s' ⇒ 
+      match s' with
+      [ inl s2 ⇒ let 〈news2,m〉 ≝ trans sig n M2 〈s2,a〉 in
+         〈inr … (inl … news2),m〉
+      | inr s3 ⇒ let 〈news3,m〉 ≝ trans sig n M3 〈s3,a〉 in
+         〈inr … (inr … news3),m〉
+      ]
+  ]. 
+ 
+definition ifTM ≝ λsig,n. λcondM,thenM,elseM : mTM sig n.
+  λqacc: states sig n condM.
+  mk_mTM sig n
+    (FinSum (states sig n condM) (FinSum (states sig n thenM) (states sig n elseM)))
+    (if_trans sig n condM thenM elseM qacc)
+    (inl … (start sig n condM))
+    (λs.match s with
+      [ inl _ ⇒ false 
+      | inr s' ⇒ match s' with 
+        [ inl s2 ⇒ halt sig n thenM s2
+        | inr s3 ⇒ halt sig n elseM s3 ]]).
+
+(****************************** lifting lemmas ********************************)
+lemma trans_if_liftM1 : ∀sig,n,M1,M2,M3,acc,s,a,news,move.
+  halt ?? M1 s = false → 
+  trans sig n M1 〈s,a〉 = 〈news,move〉 → 
+  trans sig n (ifTM sig n M1 M2 M3 acc) 〈inl … s,a〉 = 〈inl … news,move〉.
+#sig #n * #Q1 #T1 #init1 #halt1 #M2 #M3 #acc #s #a #news #move
+#Hhalt #Htrans whd in ⊢ (??%?); >Hhalt >Htrans %
+qed.
+
+lemma trans_if_liftM2 : ∀sig,n,M1,M2,M3,acc,s,a,news,move.
+  halt ?? M2 s = false → 
+  trans sig n M2 〈s,a〉 = 〈news,move〉 → 
+  trans sig n (ifTM sig n M1 M2 M3 acc) 〈inr … (inl … s),a〉 = 〈inr… (inl … news),move〉.
+#sig #n #M1 * #Q2 #T2 #init2 #halt2 #M3 #acc #s #a #news #move
+#Hhalt #Htrans whd in ⊢ (??%?); >Hhalt >Htrans %
+qed.
+
+lemma trans_if_liftM3 : ∀sig,n,M1,M2,M3,acc,s,a,news,move.
+  halt ?? M3 s = false → 
+  trans sig n M3 〈s,a〉 = 〈news,move〉 → 
+  trans sig n (ifTM sig n M1 M2 M3 acc) 〈inr … (inr … s),a〉 = 〈inr… (inr … news),move〉.
+#sig #n #M1 * #Q2 #T2 #init2 #halt2 #M3 #acc #s #a #news #move
+#Hhalt #Htrans whd in ⊢ (??%?); >Hhalt >Htrans %
+qed.
+
+lemma step_if_liftM1 : ∀sig,n,M1,M2,M3,acc,c0.
+ halt ?? M1 (cstate ??? c0) = false → 
+ step sig n (ifTM sig n M1 M2 M3 acc) (lift_confL sig n (states ?? M1) ? c0) =
+ lift_confL sig n (states ?? M1) ? (step sig n M1 c0).
+#sig #n #M1 #M2 #M3 #acc * #s #t
+  lapply (refl ? (trans ??? 〈s,current_chars sig n t〉))
+  cases (trans ??? 〈s,current_chars sig n t〉) in ⊢ (???% → %);
+  #s0 #m0 #Heq #Hhalt
+  whd in ⊢ (???(?????%)); >Heq whd in ⊢ (???%);
+  whd in ⊢ (??(????%)?); whd in ⊢ (??%?); >(trans_if_liftM1 … Hhalt Heq) //
+qed.
+
+lemma step_if_liftM2 : ∀sig,n,M1,M2,M3,acc,c0.
+ halt ?? M2 (cstate ??? c0) = false → 
+ step sig n (ifTM sig n M1 M2 M3 acc) (lift_confR sig ??? (lift_confL sig ??? c0)) =
+ lift_confR sig ??? (lift_confL sig ??? (step sig n M2 c0)).
+#sig #n #M1 (* * #Q1 #T1 #init1 #halt1 *) #M2 #M3 #acc * #s #t
+  lapply (refl ? (trans ??? 〈s,current_chars sig n t〉))
+  cases (trans ??? 〈s,current_chars sig n t〉) in ⊢ (???% → %);
+  #s0 #m0 #Heq #Hhalt
+  whd in match (step ?? M2 ?); >Heq whd in ⊢ (???%);
+  whd in ⊢ (??(????%)?); whd in ⊢ (??%?); >(trans_if_liftM2 … Hhalt Heq) //
+qed.
+
+lemma step_if_liftM3 : ∀sig,n,M1,M2,M3,acc,c0.
+ halt ?? M3 (cstate ??? c0) = false → 
+ step sig n (ifTM sig n M1 M2 M3 acc) (lift_confR sig ??? (lift_confR sig ??? c0)) =
+ lift_confR sig ??? (lift_confR sig ??? (step sig n M3 c0)).
+#sig #n #M1 #M2 #M3 #acc * #s #t
+  lapply (refl ? (trans ??? 〈s,current_chars sig n t〉))
+  cases (trans ??? 〈s,current_chars sig n t〉) in ⊢ (???% → %);
+  #s0 #m0 #Heq #Hhalt
+  whd in match (step ?? M3 ?); >Heq whd in ⊢ (???%);
+  whd in ⊢ (??(????%)?); whd in ⊢ (??%?); >(trans_if_liftM3 … Hhalt Heq) //
+qed.
+
+lemma trans_if_M1true_acc : ∀sig,n,M1,M2,M3,acc,s,a.
+  halt ?? M1 s = true → s==acc = true →
+  trans sig n (ifTM sig n M1 M2 M3 acc) 〈inl … s,a〉 = 
+    〈inr … (inl … (start ?? M2)),null_action ??〉.
+#sig #n #M1 #M2 #M3 #acc #s #a #Hhalt #Hacc whd in ⊢ (??%?); >Hhalt >Hacc %
+qed.
+
+lemma trans_if_M1true_notacc : ∀sig,n,M1,M2,M3,acc,s,a.
+  halt ?? M1 s = true → s==acc = false →
+  trans sig n (ifTM sig n M1 M2 M3 acc) 〈inl … s,a〉 = 
+    〈inr … (inr … (start ?? M3)),null_action ??〉.
+#sig #n #M1 #M2 #M3 #acc #s #a #Hhalt #Hacc whd in ⊢ (??%?); >Hhalt >Hacc %
+qed.
+
+(******************************** semantics ***********************************)
+lemma sem_if: ∀sig,n.∀M1,M2,M3:mTM sig n.∀Rtrue,Rfalse,R2,R3,acc.
+  M1 ⊨ [acc: Rtrue,Rfalse] → M2 ⊨ R2 → M3 ⊨ R3 → 
+    ifTM sig n M1 M2 M3 acc ⊨ (Rtrue ∘ R2) ∪ (Rfalse ∘ R3).
+#sig #n #M1 #M2 #M3 #Rtrue #Rfalse #R2 #R3 #acc #HaccR #HR2 #HR3 #t 
+cases (HaccR t) #k1 * #outc1 * * #Hloop1 #HMtrue #HMfalse 
+cases (true_or_false (cstate ??? outc1 == acc)) #Hacc
+  [cases (HR2 (ctapes sig ?? outc1)) #k2 * #outc2 * #Hloop2 #HM2
+   @(ex_intro … (k1+k2)) @(ex_intro … (lift_confR … (lift_confL … outc2))) %
+    [@(loop_merge ?????????
+     (mk_mconfig ? (FinSum (states sig n M1) (FinSum (states sig n M2) (states sig n M3))) n
+      (inr (states sig n M1) ? (inl (states sig n M2) (states sig n M3) (start sig n M2))) (ctapes ??? outc1) )
+     ? 
+     (loop_lift ??? 
+       (lift_confL sig n (states ?? M1) (FinSum (states ?? M2) (states ?? M3)))
+       (step sig n M1) (step sig n (ifTM sig n M1 M2 M3 acc)) 
+       (λc.halt sig n M1 (cstate … c)) 
+       (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+       … Hloop1))
+      [* *
+        [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+        | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+      |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+      |#x <p_halt_liftL %
+      |whd in ⊢ (??%?); >(mconfig_expand ??? outc1)
+       whd in match (lift_confL ?????);
+       >(trans_if_M1true_acc … Hacc) 
+        [@mconfig_eq // (* whd in ⊢ (??%?); *)
+         <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); % 
+        |@(loop_Some ?????? Hloop1)]
+      |cases outc1 #s1 #t1 %
+      |@(loop_lift ??? 
+         (λc.(lift_confR … (lift_confL sig n (states ?? M2) (states ?? M3) c)))
+         … Hloop2) 
+        [ * #s2 #t2 %
+        | #c0 #Hhalt >(step_if_liftM2 … Hhalt) // ]
+      ]
+    |%1 @(ex_intro … (ctapes ??? outc1)) % 
+      [@HMtrue @(\P Hacc) | >(mconfig_expand ??? outc2) @HM2 ]
+    ]
+  |cases (HR3 (ctapes sig ?? outc1)) #k2 * #outc2 * #Hloop2 #HM3
+   @(ex_intro … (k1+k2)) @(ex_intro … (lift_confR … (lift_confR … outc2))) %
+    [@(loop_merge ?????????
+     (mk_mconfig ? (FinSum (states sig ? M1) (FinSum (states sig ? M2) (states sig ? M3))) n
+      (inr (states sig ? M1) ? (inr (states sig ? M2) (states sig ? M3) (start sig ? M3))) (ctapes ??? outc1) )
+     ? 
+     (loop_lift ??? 
+       (lift_confL sig n (states ?? M1) (FinSum (states ?? M2) (states ?? M3)))
+       (step sig n M1) (step sig n (ifTM sig n M1 M2 M3 acc)) 
+       (λc.halt sig n M1 (cstate … c)) 
+       (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+       … Hloop1))
+      [* *
+        [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+        | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+      |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+      |#x <p_halt_liftL %
+      |whd in ⊢ (??%?); >(mconfig_expand ??? outc1);
+       whd in match (lift_confL ?????);
+       >(trans_if_M1true_notacc … Hacc) 
+        [@mconfig_eq // (* whd in ⊢ (??%?); *)
+         <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); %  
+        |@(loop_Some ?????? Hloop1)]
+      |cases outc1 #s1 #t1 %
+      |@(loop_lift ??? 
+         (λc.(lift_confR … (lift_confR sig n (states ?? M2) (states ?? M3) c)))
+         … Hloop2) 
+        [ * #s2 #t2 %
+        | #c0 #Hhalt >(step_if_liftM3 … Hhalt) // ]
+      ]
+    |%2 @(ex_intro … (ctapes ??? outc1)) % 
+      [@HMfalse @(\Pf Hacc) | >(mconfig_expand ??? outc2) @HM3 ]
+    ]
+  ]
+qed.
+
+lemma sem_if_app: ∀sig,n,M1,M2,M3,Rtrue,Rfalse,R2,R3,R4,acc.
+  accRealize sig n M1 acc Rtrue Rfalse  → M2 ⊨ R2  → M3 ⊨ R3 →  
+    (∀t1,t2,t3. (Rtrue t1 t3 → R2 t3 t2) ∨ (Rfalse t1 t3 → R3 t3 t2) → R4 t1 t2) → 
+    ifTM sig n M1 M2 M3 acc ⊨ R4.
+#sig #n #M1 #M2 #M3 #Rtrue #Rfalse #R2 #R3 #R4 #acc
+#HRacc #HRtrue #HRfalse #Hsub
+#t cases (sem_if … HRacc HRtrue HRfalse t)
+#k * #outc * #Hloop #Houtc @(ex_intro … k) @(ex_intro … outc)
+% [@Hloop] cases Houtc
+  [* #t3 * #Hleft #Hright @(Hsub … t3) %1 /2/
+  |* #t3 * #Hleft #Hright @(Hsub … t3) %2 /2/ ]
+qed.
+ 
+(* we can probably use acc_sem_if to prove sem_if *)
+(* for sure we can use acc_sem_if_guarded to prove acc_sem_if *)
+lemma acc_sem_if: ∀sig,n,M1,M2,M3,Rtrue,Rfalse,R2,R3,acc.
+  M1 ⊨ [acc: Rtrue, Rfalse]  → M2 ⊨ R2 → M3 ⊨ R3 → 
+  ifTM sig n M1 (single_finalTM … M2) M3 acc ⊨
+     [inr … (inl … (inr … start_nop)): Rtrue ∘ R2, Rfalse ∘ R3].
+#sig #n #M1 #M2 #M3 #Rtrue #Rfalse #R2 #R3 #acc #HaccR #HR2 #HR3 #t 
+cases (HaccR t) #k1 * #outc1 * * #Hloop1 #HMtrue #HMfalse 
+cases (true_or_false (cstate ??? outc1 == acc)) #Hacc
+  [lapply (sem_single_final … HR2) -HR2 #HR2
+   cases (HR2 (ctapes sig ?? outc1)) #k2 * #outc2 * #Hloop2 #HM2
+   @(ex_intro … (k1+k2)) 
+   @(ex_intro … (lift_confR … (lift_confL … outc2))) %
+    [%
+      [@(loop_merge ?????????
+         (mk_mconfig ? (states sig n (ifTM sig n M1 (single_finalTM … M2) M3 acc)) n
+          (inr (states sig n M1) ? (inl ? (states sig n M3) (start sig n (single_finalTM sig n M2)))) (ctapes ??? outc1) )
+         ? 
+         (loop_lift ??? 
+          (lift_confL sig n (states ?? M1) (FinSum (states ?? (single_finalTM … M2)) (states ?? M3)))
+          (step sig n M1) (step sig n (ifTM sig n M1 (single_finalTM ?? M2) M3 acc)) 
+          (λc.halt sig n M1 (cstate … c)) 
+          (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+          … Hloop1))
+        [* *
+          [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+          | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+        |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+        |#x <p_halt_liftL %
+        |whd in ⊢ (??%?); >(mconfig_expand ??? outc1);
+         whd in match (lift_confL ????);
+         >(trans_if_M1true_acc … Hacc) 
+          [@mconfig_eq // (* whd in ⊢ (??%?); *)
+           <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); % 
+          | @(loop_Some ?????? Hloop1)]
+        |cases outc1 #s1 #t1 %
+        |@(loop_lift ??? 
+           (λc.(lift_confR … (lift_confL sig n (states ?? (single_finalTM ?? M2)) (states ?? M3) c)))
+           … Hloop2) 
+          [ * #s2 #t2 %
+          | #c0 #Hhalt >(step_if_liftM2 … Hhalt) // ]
+        ]
+      |#_ @(ex_intro … (ctapes ??? outc1)) % 
+        [@HMtrue @(\P Hacc) | >(mconfig_expand ??? outc2) @HM2 ]
+      ]
+    |>(mconfig_expand ??? outc2) whd in match (lift_confR ?????);
+     * #H @False_ind @H @eq_f @eq_f >(mconfig_expand ??? outc2)
+     @single_final // @(loop_Some ?????? Hloop2)
+    ]
+  |cases (HR3 (ctapes sig ?? outc1)) #k2 * #outc2 * #Hloop2 #HM3
+   @(ex_intro … (k1+k2)) @(ex_intro … (lift_confR … (lift_confR … outc2))) %
+    [%
+      [@(loop_merge ?????????
+         (mk_mconfig ? (states sig n (ifTM sig n M1 (single_finalTM … M2) M3 acc)) n
+          (inr (states sig n M1) ? (inr (states sig n (single_finalTM ?? M2)) ? (start sig n M3))) (ctapes ??? outc1) )
+         ? 
+         (loop_lift ??? 
+          (lift_confL sig n (states ?? M1) (FinSum (states ?? (single_finalTM … M2)) (states ?? M3)))
+          (step sig n M1) (step sig n (ifTM sig n M1 (single_finalTM ?? M2) M3 acc)) 
+          (λc.halt sig n M1 (cstate … c)) 
+          (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+          … Hloop1))
+        [* *
+          [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+          | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+        |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+        |#x <p_halt_liftL %
+        |whd in ⊢ (??%?); >(mconfig_expand ??? outc1);
+         whd in match (lift_confL ?????);
+         >(trans_if_M1true_notacc … Hacc) 
+          [@mconfig_eq // (* whd in ⊢ (??%?); *)
+           <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); % 
+          |@(loop_Some ?????? Hloop1)]
+        |cases outc1 #s1 #t1 %
+        |@(loop_lift ??? 
+           (λc.(lift_confR … (lift_confR sig n (states ?? (single_finalTM ?? M2)) (states ?? M3) c)))
+           … Hloop2) 
+          [ * #s2 #t2 %
+          | #c0 #Hhalt >(step_if_liftM3 … Hhalt) // ]
+        ]
+      |>(mconfig_expand ??? outc2) whd in match (lift_confR ?????);
+       #H destruct (H) 
+      ]
+    |#_ @(ex_intro … (ctapes ??? outc1)) % 
+      [@HMfalse @(\Pf Hacc) | >(mconfig_expand ??? outc2) @HM3 ]
+    ]
+  ]
+qed.
+    
+lemma acc_sem_if_app: ∀sig,n,M1,M2,M3,Rtrue,Rfalse,R2,R3,R4,R5,acc.
+  M1 ⊨ [acc: Rtrue, Rfalse] → M2 ⊨ R2 → M3 ⊨ R3 → 
+    (∀t1,t2,t3. Rtrue t1 t3 → R2 t3 t2 → R4 t1 t2) → 
+    (∀t1,t2,t3. Rfalse t1 t3 → R3 t3 t2 → R5 t1 t2) → 
+     ifTM sig n M1 (single_finalTM … M2) M3 acc ⊨ 
+       [inr … (inl … (inr … start_nop)): R4, R5].    
+#sig #n #M1 #M2 #M3 #Rtrue #Rfalse #R2 #R3 #R4 #R5 #acc
+#HRacc #HRtrue #HRfalse #Hsub1 #Hsub2 
+#t cases (acc_sem_if … HRacc HRtrue HRfalse t)
+#k * #outc * * #Hloop #Houtc1 #Houtc2 @(ex_intro … k) @(ex_intro … outc)
+% [% [@Hloop
+     |#H cases (Houtc1 H) #t3 * #Hleft #Hright @Hsub1 // ]
+  |#H cases (Houtc2 H) #t3 * #Hleft #Hright @Hsub2 // ]
+qed.
+
+lemma sem_single_final_guarded: ∀sig,n.∀M: mTM sig n.∀Pre,R.
+  GRealize sig n M Pre R → GRealize sig n (single_finalTM sig n M) Pre R.
+#sig #n #M #Pre #R #HR #intape #HPre 
+cases (sem_seq_guarded ???????? HR (Realize_to_GRealize ??? (λt.True) ? (sem_nop …)) ?? HPre) //
+#k * #outc * #Hloop * #ta * #Hta whd in ⊢ (%→?); #Houtc
+@(ex_intro ?? k) @(ex_intro ?? outc) %  [ @Hloop | >Houtc // ]
+qed.
+    
+lemma acc_sem_if_guarded: ∀sig,n.∀M1,M2,M3: mTM sig n.∀P,P2,Rtrue,Rfalse,R2,R3,acc.
+  M1 ⊨ [acc: Rtrue, Rfalse]  → 
+  (GRealize ?? M2 P2 R2) → (∀t,t0.P t → Rtrue t t0 → P2 t0) → 
+  M3 ⊨ R3 → 
+  accGRealize ?? (ifTM sig n M1 (single_finalTM … M2) M3 acc) 
+    (inr … (inl … (inr … start_nop))) P (Rtrue ∘ R2) (Rfalse ∘ R3).
+#sig #n #M1 #M2 #M3 #P #P2 #Rtrue #Rfalse #R2 #R3 #acc #HaccR #HR2 #HP2 #HR3 #t #HPt 
+cases (HaccR t) #k1 * #outc1 * * #Hloop1 #HMtrue #HMfalse 
+cases (true_or_false (cstate ??? outc1 == acc)) #Hacc
+  [lapply (sem_single_final_guarded … HR2) -HR2 #HR2
+   cases (HR2 (ctapes sig ?? outc1) ?)
+   [|@HP2 [||@HMtrue @(\P Hacc)] // ]
+   #k2 * #outc2 * #Hloop2 #HM2
+   @(ex_intro … (k1+k2)) 
+   @(ex_intro … (lift_confR … (lift_confL … outc2))) %
+    [%
+      [@(loop_merge ?????????
+         (mk_mconfig ? (states sig n (ifTM sig n M1 (single_finalTM … M2) M3 acc)) n
+          (inr (states sig n M1) ? (inl ? (states sig n M3) (start sig n (single_finalTM sig n M2)))) (ctapes ??? outc1) )
+         ? 
+         (loop_lift ??? 
+          (lift_confL sig n (states ?? M1) (FinSum (states ?? (single_finalTM … M2)) (states ?? M3)))
+          (step sig n M1) (step sig n (ifTM sig n M1 (single_finalTM ?? M2) M3 acc)) 
+          (λc.halt sig n M1 (cstate … c)) 
+          (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+          … Hloop1))
+        [* *
+          [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+          | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+        |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+        |#x <p_halt_liftL %
+        |whd in ⊢ (??%?); >(mconfig_expand ??? outc1);
+         whd in match (lift_confL ?????);
+         >(trans_if_M1true_acc … Hacc) 
+          [@mconfig_eq // (* whd in ⊢ (??%?); *)
+           <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); % 
+          | @(loop_Some ?????? Hloop1)]
+        |cases outc1 #s1 #t1 %
+        |@(loop_lift ??? 
+           (λc.(lift_confR … (lift_confL sig n (states ?? (single_finalTM ?? M2)) (states ?? M3) c)))
+           … Hloop2) 
+          [ * #s2 #t2 %
+          | #c0 #Hhalt >(step_if_liftM2 … Hhalt) // ]
+        ]
+      |#_ @(ex_intro … (ctapes ??? outc1)) % 
+        [@HMtrue @(\P Hacc) | >(mconfig_expand ??? outc2) @HM2 ]
+      ]
+    |>(mconfig_expand ??? outc2) whd in match (lift_confR ?????);
+     * #H @False_ind @H @eq_f @eq_f >(mconfig_expand ??? outc2)
+     @single_final // @(loop_Some ?????? Hloop2)
+    ]
+  |cases (HR3 (ctapes sig ?? outc1)) #k2 * #outc2 * #Hloop2 #HM3
+   @(ex_intro … (k1+k2)) @(ex_intro … (lift_confR … (lift_confR … outc2))) %
+    [%
+      [@(loop_merge ?????????
+         (mk_mconfig ? (states sig n (ifTM sig n M1 (single_finalTM … M2) M3 acc)) n
+          (inr (states sig n M1) ? (inr (states sig n (single_finalTM ?? M2)) ? (start sig n M3))) (ctapes ??? outc1) )
+         ? 
+         (loop_lift ??? 
+          (lift_confL sig n (states ?? M1) (FinSum (states ?? (single_finalTM … M2)) (states ?? M3)))
+          (step sig n M1) (step sig n (ifTM sig n M1 (single_finalTM ?? M2) M3 acc)) 
+          (λc.halt sig n M1 (cstate … c)) 
+          (λc.halt_liftL ?? (halt sig n M1) (cstate … c)) 
+          … Hloop1))
+        [* *
+          [ #sl #tl whd in ⊢ (??%? → ?); #Hl %
+          | #sr #tr whd in ⊢ (??%? → ?); #Hr destruct (Hr) ]
+        |#c0 #Hhalt >(step_if_liftM1 … Hhalt) // 
+        |#x <p_halt_liftL %
+        |whd in ⊢ (??%?); >(mconfig_expand ??? outc1);
+         whd in match (lift_confL ?????);
+         >(trans_if_M1true_notacc … Hacc) 
+          [@mconfig_eq // (* whd in ⊢ (??%?); *)
+           <(tape_move_null_action sig n (ctapes sig (states sig n M1) n outc1)) in ⊢ (???%); % 
+          | @(loop_Some ?????? Hloop1)]
+        |cases outc1 #s1 #t1 %
+        |@(loop_lift ??? 
+           (λc.(lift_confR … (lift_confR sig n (states ?? (single_finalTM ?? M2)) (states ?? M3) c)))
+           … Hloop2) 
+          [ * #s2 #t2 %
+          | #c0 #Hhalt >(step_if_liftM3 … Hhalt) // ]
+        ]
+      |>(mconfig_expand ??? outc2) whd in match (lift_confR ?????);
+       #H destruct (H) 
+      ]
+    |#_ @(ex_intro … (ctapes ??? outc1)) % 
+      [@HMfalse @(\Pf Hacc) | >(mconfig_expand ??? outc2) @HM3 ]
+    ]
+  ]
+qed.
+    
+lemma acc_sem_if_app_guarded: ∀sig,n,M1,M2,M3,P,P2,Rtrue,Rfalse,R2,R3,R4,R5,acc.
+  M1 ⊨ [acc: Rtrue, Rfalse] → 
+  (GRealize ? n M2 P2 R2) → (∀t,t0.P t → Rtrue t t0 → P2 t0) → 
+  M3 ⊨ R3 → 
+  (∀t1,t2,t3. Rtrue t1 t3 → R2 t3 t2 → R4 t1 t2) → 
+  (∀t1,t2,t3. Rfalse t1 t3 → R3 t3 t2 → R5 t1 t2) → 
+  accGRealize ? n (ifTM sig n M1 (single_finalTM … M2) M3 acc) 
+    (inr … (inl … (inr … start_nop))) P R4 R5 .
+#sig #n #M1 #M2 #M3 #P #P2 #Rtrue #Rfalse #R2 #R3 #R4 #R5 #acc
+#HRacc #HRtrue #Hinv #HRfalse #Hsub1 #Hsub2 
+#t #HPt cases (acc_sem_if_guarded … HRacc HRtrue Hinv HRfalse t HPt)
+#k * #outc * * #Hloop #Houtc1 #Houtc2 @(ex_intro … k) @(ex_intro … outc)
+% [% [@Hloop
+     |#H cases (Houtc1 H) #t3 * #Hleft #Hright @Hsub1 // ]
+  |#H cases (Houtc2 H) #t3 * #Hleft #Hright @Hsub2 // ]
+qed.
+
+