Goal:
  
  A : Type
  R : A → A → Type
  a : A
  l : list A
  X : All2 R (a :: l) (a :: l)
  x : A
  y : A
  l0 : list A
  l' : list A
  X0 : R a a
  X1 : All2 R l l
  H0 : x = a
  H1 : l0 = l
  H : y = a
  H3 : l' = l
  X2 : All (λ x : A, R x x) l
  ============================
   (R a a)


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