Goal:
  
  A : Type
  B : Type
  C : Type
  P : A → B → C → Type
  a : C
  ls1 : list C
  a0 : A
  ls2 : list A
  b : B
  ls3 : list B
  X1 : All2 (λ (x : A) (y : B), All (P x y) (a :: ls1)) ls2 ls3
  X : P a0 b a
  X2 : All (P a0 b) ls1
  ============================
   (∀ (x : A) (y : B),
      (λ (x0 : A) (y0 : B), All (P x0 y0) (a :: ls1)) x y → All (P x y) ls1)


DEBUG:Going to execute:
cbn
Level 1: Backtrace:

No applicable tactic.
Level 0: Backtrace:

No applicable tactic.