Goal:
    _z_ : VSet.t  a : V.t
  ============================
   (VSet.In a _z_ <-> VSet.In a _z_)


DEBUG:Going to execute:
repeat
            match goal with
            | J:_ |- _ => progress change T with V.t in J
            | |- _ => progress change T with V.t
            end
DEBUG LTAC Evaluated term: VSet.elt
DEBUG LTAC Evaluated term: V.t