apply (classic (h M N)).
Qed.
(** g is included in h iff whenever (M,N) is in g then (M,N) is in h *)
Definition inclusion (g h : hedge) := forall M N : Msg, g M N -> h M N.
(** g = h iff g is included in h and h is included in g *)
Definition equal (g h : hedge) := inclusion g h /\ inclusion h g.

(* Specifications: *)
(** inclusion is reflexive, ... *)
Lemma inclusion_refl : forall h : hedge, inclusion h h.
unfold inclusion in |- *.