Goal:
    x : V.t  s : VSet.t
  ============================
   (VSet.In x s -> True)


DEBUG:Going to execute:
repeat
            match goal with
            | H:?x = ?x |- _ => clear H
            | H:?x = ?y |- _ => rewrite -> H in *; clear H
            end; autorewrite with set_eq_simpl in *