Goal:
  
  x : V.t
  y : V.t
  p : VSet.t
  H : x = y -> False
  a : V.t
  H2 : x = a
  H1 : y = a
  H3 : False
  ============================
   False


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