intros.
elim H.
elim H0.
intros.
split; apply inclusion_trans with g; trivial.
Qed.
(** union and intersection of hedges *)
Definition union (g h : hedge) (M N : Msg) := g M N \/ h M N.
Definition inter (g h : hedge) (M N : Msg) := g M N /\ h M N.

(** union is symmetric *)
Lemma union_sym : forall g h : hedge, equal (union g h) (union h g).
unfold union in |- *.