Goal:
  
  x : V.t
  p : VSet.t
  H : VSet.In x p -> False
  a : V.t
  H0 : x = a
  H1 : VSet.In a p
  ============================
   (x = a)


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 = a
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.