Goal:
  
  A : Type
  B : Type
  P : A → B → Type
  P' : ∀ (a : A) (b : B), P a b → Type
  Q' : ∀ (a : A) (b : B), P a b → Type
  l : list A
  l' : list B
  a : All2 P l l'
  ============================
   (All2_dep P' a
    → (∀ (x : A) (y : B) (r : P x y), P' x y r → Q' x y r) → All2_dep Q' a)


DEBUG:Going to execute:
induction 1; constructor