Goal:
    x1 : V.t  n1 : Z  y1 : V.t  x2 : V.t  n2 : Z  y2 : V.t  H : V.lt x2 x1
  ============================
   (V.lt x2 x1 \/
    V.eq x2 x1 /\ n2 < n1 \/ V.eq x2 x1 /\ n2 = n1 /\ V.lt y2 y1)


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