Goal:
    x2 : V.t  n2 : Z  y2 : V.t
  ============================
   ((x2, n2, y2) = (x2, n2, y2))


DEBUG:Going to execute:
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