Goal:
  
  A : Type
  P : A → A → Type
  r : A
  r' : A
  X : All2 P [r] ([] ++ [r'])
  x : A
  y : A
  l : list A
  l' : list A
  X0 : P r r'
  X1 : All2 P [] []
  H0 : x = r
  H1 : l = []
  H : y = r'
  H3 : l' = []
  ============================
   (All2 P [] [])


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