Goal:
  
  A : Type
  P : A → A → Type
  a : A
  l : list A
  a0 : A
  l' : list A
  r : A
  r' : A
  IHl : ∀ l' : list A, All2 P (l ++ [r]) (l' ++ [r']) → All2 P l l' × P r r'
  X : All2 P (a :: l ++ [r]) ((a0 :: l') ++ [r'])
  X0 : P a a0
  a1 : All2 P l l'
  b : P r r'
  ============================
   (P a a0)


DEBUG:Going to execute:
fun flags =>
             match reverse goal with
             | |- ?X1 =>
                   <Coq.Init.Tauto.is_unit_or_eq> flags X1; constructor 1
             | H:?X1 |- _ => <Coq.Init.Tauto.is_empty> flags X1; elim H
             | _ => Ltac.assumption
             end