Goal:
    x : V.t  s : VSet.t  y : V.t  H0 : x = y -> False  H1 : VSet.In y s
  ============================
   (VSet.In y s)


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; elim id; do 2 intro; clear id
Level 4: evaluation returns
<coq-core.plugins.tauto::is_conj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := x = y -> False
of type
constr of type tacvalue

Level 4: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.
Level 3: Backtrace:

Tactic failure.