Goal:
    _z_ : VSet.t  x0 : V.t  x1 : V.t  x2 : V.t  a : V.t  H : x2 = a
  ============================
   (x1 = a)


DEBUG:Going to execute:
match goal with
           | |- _ -> _ => intro; t_tauto_intuit
           | |- _ => t_reduce; t_solver
           end || t_solver
Level 5: evaluation returns
<coq-core.plugins.tauto::is_disj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := x1 = a
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.
Level 3: Backtrace:

Tactic failure.