Goal:
  
  x : V.t
  y : V.t
  p : VSet.t
  H : x = y -> False
  a : V.t
  H1 : VSet.In a p
  H2 : y = a
  H4 : False
  H0 : False
  ============================
   False


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 5: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := False
of type
constr of type tacvalue

Level 5: Backtrace:

Tactic failure.
Level 5: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.