Goal:
  
  s : VSet.t
  s' : VSet.t
  s'' : VSet.t
  i : V.t
  H1 : VSet.In i s
  H2 : VSet.In i s''
  H3 : VSet.In i s''
  H0 : VSet.In i s'
  H4 : False
  ============================
   (VSet.In i s')


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; Ltac.split
Level 3: 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 3: Backtrace:

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

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

Tactic failure: No matching clause.
Level 2: Backtrace:

Tactic failure: No matching clause.