Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → C → Type
  c : C
  a : C
  ls1 : list C
  a0 : A
  ls2 : list A
  b : B
  ls3 : list B
  X : P a0 b c
  X2 : All2 (λ (x : A) (y : B), P x y c) ls2 ls3
  X3 : All
         (λ z : C, All2 (λ (x : A) (y : B), P x y z) (a0 :: ls2) (b :: ls3))
         ls1
  X1 : P a0 b a
  X4 : All2 (λ (x : A) (y : B), P x y a) ls2 ls3
  x : A
  y : B
  X0 : (λ (x : A) (y : B), All (P x y) (c :: ls1)) x y
  x0 : C
  ============================
   (All2 (λ (x : A) (y : B), P x y x0) (a0 :: ls2) (b :: ls3) → P x y x0)


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

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.
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Proof is not complete.
Level 0: Backtrace:

Proof is not complete.