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


DEBUG:Going to execute:
constructor 1
Level 5: evaluation returns
<coq-core.plugins.tauto::is_unit_or_eq@0>
where
tauto_flags := 
of type
tauto_flags
X1 := y = a
of type
constr of type tacvalue