simple induction E; intros A f HR; simple induction E'; intros A' f' HR'.
intros e E'' p p'.
elim e; intros e1 e2.
split.
intros o.
elim o; intros o1 o2.
simpl in |- *.
split.
intros a' i.
elim (e2 a'); intros a eq.
cut (INC (f' a') (f a)).
intros inc.
elim (HR a (f' a') eq (f' a') inc (INC_refl (f' a'))).
intros h1 h2.
auto with zfc.
apply h1.
apply ord_ext with (f a) (INC_refl (f a)).
auto with zfc.
auto with zfc.
apply o1.
apply IN_sound_left with (f' a'); auto with zfc.
auto with zfc.
intros a' E0 i inc.
intros or.
elim (e2 a'); intros a eq.
cut (INC E0 (f a)).
intros inc0.
apply (o2 a E0) with inc0.
apply IN_sound_left with (f' a'); auto with zfc.
elim (HR a (f' a')) with (E'' := E0) (p := inc0) (p' := inc).
intros h1 h2.
auto with zfc.
auto with zfc.
apply INC_sound_right with (f' a'); auto with zfc.
intros o; elim o; intros o1 o2.
split.
intros a i.
elim (e1 a); intros a' eq.
cut (INC (f a) (f' a')); auto with zfc.
cut (INC (f' a') (f a)); auto with zfc.
intros inc1 inc2.
elim (HR a (f' a')) with (E'' := f a) (p := INC_refl (f a)) (p' := inc2).
intros h1 h2.
apply h2.
apply ord_ext with (E' := f' a') (p' := INC_refl (f' a')).
auto with zfc.
auto with zfc.
apply o1.
apply IN_sound_left with (f a); auto with zfc.
auto with zfc.
intros a E0 i inc ord0.
elim (e1 a); intros a' eq.
cut (INC E0 (f' a')).
intros inc0.
apply (o2 a') with (p := inc0).
apply IN_sound_left with (f a); auto with zfc.
elim (HR a (f' a') eq E0 inc inc0).
intros h1 h2.
auto with zfc.
apply INC_sound_right with (f a); auto with zfc.
Qed.
Definition Ord (E : Ens) := ord E E (INC_refl E).

Lemma Ord_sound : forall E E' : Ens, EQ E E' -> Ord E -> Ord E'.
unfold Ord in |- *.