Goal:
    s : VSet.t  s'' : VSet.t  x : V.t  H0 : VSet.In x s  H : False
  ============================
   (VSet.In x s'')


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