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


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 4: evaluation returns
<coq-core.plugins.tauto::is_empty@0>
where
tauto_flags := 
of type
tauto_flags
X1 := Z
of type
constr of type tacvalue

Level 4: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.