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


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 3: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := V.lt x2 x2 \/
      V.eq x2 x2 /\ n2 < n2 \/ V.eq x2 x2 /\ n2 = n2 /\ V.lt y1 y2
of type
constr of type tacvalue

Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.