Goal:
  
  A : Type
  B : Type
  P : list A → list A → A → A → B → Type
  b : B
  a : B
  ls1 : list B
  a0 : A
  ls2 : list A
  a1 : A
  ls3 : list A
  X : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y b) ls2 ls3
  X2 : P ls2 ls3 a0 a1 b
  X3 : All
         (λ z : B,
            All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y z)
              (a0 :: ls2) (a1 :: ls3)) ls1
  X1 : All2_fold (λ (l1 l2 : list A) (x y : A), P l1 l2 x y a) ls2 ls3
  X4 : P ls2 ls3 a0 a1 a
  Γ : list A
  Γ' : list A
  d : A
  d' : A
  X0 : (λ (l1 l2 : list A) (x y : A), All (P l1 l2 x y) (b :: ls1)) Γ Γ' d d'
  x : B
  ============================
   (All2_fold (λ (l1 l2 : list A) (x0 y : A), P l1 l2 x0 y x) 
      (a0 :: ls2) (a1 :: ls3) → P Γ Γ' d d' x)


DEBUG:Going to execute:
constructor
Level 0: Backtrace:

Proof is not complete.
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Proof is not complete.
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Proof is not complete.
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Proof is not complete.
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Proof is not complete.