Goal:
  
  A : Type
  B : Type
  P : list A → list A → A → A → B → Type
  a : 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 a) ls2 ls3
  X2 : P ls2 ls3 a0 a1 a
  Γ : list A
  Γ' : list A
  d : A
  d' : A
  ============================
   (P Γ Γ' d d' a → All (P Γ Γ' d d') [])


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

The type of X0 is not inductive.