Section Second.
Variable H : Ensemble U.
Variable witness : U.
Variable h0 : In U H witness.
Variable h1 : Included U H G.
Variable h2 : forall a b : U, In U H a -> In U H b -> In U H (star a (inv b)).
Let eH : U := star witness (inv witness).
End Second.

Lemma Ex4 : powers e = Singleton U e.