Goal:
    x : V.t  y : V.t  p : VSet.t  a : V.t  H : VSet.In a p
  ============================
   (x = a \/ VSet.In a p)


DEBUG:Going to execute:
Ltac.assumption
Level 5: evaluation returns
<coq-core.plugins.tauto::is_empty@0>
where
tauto_flags := 
of type
tauto_flags
X1 := VSet.In a p
of type
constr of type tacvalue

Level 5: Backtrace:

Tactic failure.
Level 5: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.
Level 4: Backtrace:

Tactic failure.