unfold le_h in |- *.
unfold inclusion in |- *.
intros.
generalize H1.
generalize (H M N H1).
unfold reduce in |- *.
case M; try tauto.
case N; try tauto.
intros.
elim H3.
split; trivial.
case H5.
intro.
left.
red in |- *; intro.
apply H6.
generalize (inclusion_impl_le_h (reduce g) g (red_incl_h g)).
unfold le_h in |- *.
unfold inclusion in |- *.
intros.
apply H8.
apply H0.
trivial.
intro.
right; red in |- *; intro; apply H6.
generalize (inclusion_impl_le_h (reduce g) g (red_incl_h g)).
unfold le_h in |- *.
unfold inclusion in |- *.
intros.
apply H8.
apply H0.
trivial.
case N; try tauto.
intros.
split; trivial.
elim H3; intros.
case H5.
left; red in |- *; intro; apply H6.
generalize (inclusion_impl_le_h (reduce g) g (red_incl_h g)).
unfold le_h in |- *.
unfold inclusion in |- *; auto.
right; red in |- *; intro; apply H6.
generalize (inclusion_impl_le_h (reduce g) g (red_incl_h g)).
unfold le_h in |- *.
unfold inclusion in |- *; auto.
case N; try tauto.
intros.
split; trivial.
elim H3.
intros.
case H5; try tauto.
right.
red in |- *; intro.
apply H6.
generalize (inclusion_impl_le_h (reduce g) g (red_incl_h g)).
unfold le_h in |- *.
unfold inclusion in |- *; auto.
Qed.

(* Specifications: *)
(** reduce is idempotent *)
Lemma reduce_idempotent :
forall h : hedge, equal (reduce h) (reduce (reduce h)).