(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
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(* File: axs_paire.v                                                       *)
(* auteur: alex@sysal.ibp.fr                                               *)
(* date: 19/10/95                                                          *)
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Require Export axs_extensionnalite.
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(* Axiome de la paire                                                      *)
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Parameter paire : E -> E -> E.
Axiom
axs_paire : forall v0 v1 v3 : E, In v3 (paire v0 v1) <-> v3 = v0 \/ v3 = v1.
(* Proof of lem_paire_unique                                               *)
intros.
apply axs_extensionnalite; intros.
generalize (H v2); clear H; unfold iff in |- *; intros.
elim H; clear H; intros.
generalize (axs_paire a b); unfold iff in |- *; intros.
generalize (H1 v2); clear H1; intros.
elim H1; clear H1; intros.
split; intros.
clear H0; clear H1; auto.
clear H; clear H2; auto.
Qed.
(* End of proof of lem_paire_unique                                        *)
(* Proof of lem_paire_sym                                                  *)
intros.
apply axs_extensionnalite; intros; unfold iff in |- *; intros.
elim (axs_paire b a v2); intros.
elim (axs_paire a b v2); intros.
split; intros.
clear H; clear H2; apply H0; clear H0; apply lem_or_sym; auto.
clear H0; clear H1; apply H2; clear H2; apply lem_or_sym; auto.
Qed.
(* End of proof of lem_paire_sym                                           *)
(* Proof of lem_paire_propertie                                            *)
intros; split; intros.
apply lem_or_and_conv_r.
generalize axs_paire; intros.
split.
elim (H0 a1 b1 a0); intros.
clear H0; clear H2; apply H1; clear H1.
rewrite <- H.
elim (axs_paire a0 b0 a0); intros.
clear H0; apply H1; clear H1; left; reflexivity.
split.
apply lem_or_sym.
elim (H0 a0 b0 b1); clear H0; intros.
clear H1.
elim (lem_eq_or a0 b0 b1); intros.
clear H1; apply H2; clear H2.
apply H0; clear H0.
rewrite H.
elim (axs_paire a1 b1 b1); intros.
clear H0; apply H1; clear H1; right; reflexivity.
split.
elim (lem_eq_or a0 b0 a1); intros.
clear H1; apply H2; clear H2.
elim (H0 a0 b0 a1); clear H0; intros.
clear H1; apply H0; clear H0; rewrite H.
elim (axs_paire a1 b1 a1); intros.
clear H0; apply H1; clear H1; left; reflexivity.
apply lem_or_sym.
elim (H0 a1 b1 b0); clear H0; intros.
clear H1; apply H0; clear H0; rewrite <- H; clear H.
elim (axs_paire a0 b0 b0); intros.
clear H; apply H0; clear H0; right; reflexivity.
elim H; clear H; intros.
elim H; clear H; intros.
rewrite H; clear H; rewrite H0; clear H0; reflexivity.
elim H; clear H; intros.
rewrite H; clear H; rewrite H0; clear H0; elim (lem_paire_sym a1 b1); intros;
reflexivity.
Qed.
(* End of proof of lem_paire_propertie                                     *)
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(* Singleton                                                               *)
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Definition singleton (a : E) := paire a a.
Hint Unfold singleton: zfc.

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(* {a} = {a'} <=> a = a'                                                   *)
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Lemma lem_singleton_propertie :
forall a b : E, singleton a = singleton b <-> a = b.