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(* GNU General Public License for more details.                       *)
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(* 02110-1301 USA                                                     *)
(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
(* The set of natural numbers  *)
Definition Class_succ (E : Ens) := Union (Paire E (Sing E)).
(* Inductive Ord : Ens -> Prop := Oo : (Ord Vide) | So : (E:Ens)(Ord E)->(Ord (Class_succ E)) | Lo : (E:Ens)((e:Ens)(IN e E)->(Ord e))->(Ord (Union E)) | Eo : (E,E':Ens)(Ord E)->(EQ E E')->(Ord E').  Hints Resolve Oo So Lo : zfc. *)
Definition Nat : nat -> Ens.
simple induction 1; intros.
exact Vide.
exact (Class_succ X).
Defined.
(* Theorem Nat_Ord : (n:nat)(Ord (Nat n)). Induction n; Simpl; Auto with zfc. Save. *)
Definition Omega : Ens := sup nat Nat.
intros E; unfold Class_succ in |- *; unfold Sing in |- *;
apply IN_Union with (Paire E E); auto with zfc.
Qed.
unfold INC in |- *; unfold Class_succ in |- *.
intros.
apply IN_Union with E; auto with zfc.
Qed.
Hint Resolve IN_Class_succ INC_Class_succ: zfc.
intros E E' i.
unfold Class_succ in i.
elim (Union_IN (Paire E (Sing E)) E' i).
intros E1; simple induction 1; intros i1 i2.
elim (Paire_IN E (Sing E) E1 i1).
intros; right; apply IN_sound_right with E1; auto with zfc.
intros; left; cut (IN E' (Sing E)).
auto with zfc.
apply IN_sound_right with E1; auto with zfc.
Qed.
simple induction E; intros A f r i.
cut False.
simple induction 1.
elim (IN_EXType (sup A f) (sup A f) i); intros a e.
simpl in a.
change (EQ (sup A f) (f a)) in e.
elim (r a).
apply IN_sound_right with (sup A f); auto with zfc.
exists a; auto with zfc.
Qed.
intros; simpl in |- *; exists n; auto with zfc.
Qed.
Hint Resolve Nat_IN_Omega: zfc.
simpl in |- *; simple induction 1.
intros n e.
exists n; auto with zfc.
Qed.

Theorem IN_Nat_EXType :
forall (n : nat) (E : Ens),
IN E (Nat n) -> EXType _ (fun p : nat => EQ E (Nat p)).