Goal:
    x : V.t  s : VSet.t  y : V.t  H1 : VSet.In y s  H : x = y  H2 : False
  ============================
   False


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; Ltac.split
Level 4: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue

Level 4: Backtrace:

Tactic failure: No matching clause.
Level 4: Backtrace:

Tactic failure: No matching clause.
Level 4: Backtrace:

Tactic failure: No matching clause.
Level 3: Backtrace:

Tactic failure: No matching clause.