(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
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(* File: applications.v                                                    *)
(* auteur: alex@sysal.ibp.fr                                               *)
(* date: 19/10/95                                                          *)
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Require Export couples.
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(* Relations n-aires                                                       *)
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Definition n_aire (n : nat) (a : E) (F : E -> Prop) :=
subset F (cart_power n a).
(* Pas de reciproque (dixit pagano pb des ensembles non decidables)        *)
(* Proof of lem_subset                                                     *)
intros; elim (axs_comprehension F b y); intros.
generalize H1; rewrite <- H; clear H H1 H2; intros.
elim H1; intros; auto with zfc.
Qed.
(* End of proof of lem_subset                                              *)
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(* applications                                                            *)
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Definition fun_ (f : E) :=
(exists a : E, (exists b : E, inc f (cartesien a b))) /\
(forall x y z : E, In (couple x y) f -> In (couple x z) f -> y = z).
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(* Domaine d'une application                                               *)
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Definition dom (f : E) :=
subset (fun v0 : E => fun_ f -> exists v1 : E, In (couple v0 v1) f)
(reunion (reunion f)).
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(* Image d'une application                                                 *)
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Definition Img (f : E) :=
subset (fun v1 : E => fun_ f -> exists v0 : E, In (couple v0 v1) f)
(reunion (reunion f)).
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(* f est une application de a vers b                                       *)
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Definition fun_sig (f a b : E) := fun_ f /\ dom f = a /\ inc (Img f) b.
(* Proof of lem_fun_sig_is_fun                                             *)
unfold fun_sig in |- *; intros.
elim H; clear H; intros; auto with zfc.
Qed.
(* End of proof of lem_fun_sig_is_fun                                      *)
(* Proof of lem_fun_sig_dom                                                *)
intros; elim H; clear H; intros; elim H0; clear H0; intros; auto with zfc.
Qed.
(* End of proof of lem_fun_sig_dom                                         *)
(* Proof of lem_fun_sig_img                                                *)
intros; elim H; clear H; intros; elim H0; clear H0; intros; auto with zfc.
Qed.
(* End of proof of lem_fun_sig_img                                         *)
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(* f est une application surjective de a vers b                            *)
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Definition fun_surj (f a b : E) := fun_ f /\ dom f = a /\ Img f = b.
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(* f est une application injective                                         *)
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Definition fun_inj (f a b : E) :=
fun_ f /\
dom f = a /\
inc (Img f) b /\
(forall b : E, In b (Img f) -> exUniq _ (fun a : E => In (couple a b) f)).
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(* f est une bijection                                                     *)
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Definition fun_bij (f a b : E) :=
fun_ f /\
dom f = a /\
Img f = b /\
(forall b : E, In b (Img f) -> exUniq _ (fun a : E => In (couple a b) f)).
(* Proof of lem_surj_to_sig                                                *)
unfold fun_surj in |- *; unfold fun_sig in |- *; intros.
elim H; clear H; intros; elim H0; clear H0; intros.
split;
[ auto with zfc
| split; [ auto with zfc | unfold inc in |- *; intros ] ].
generalize H2; rewrite H1; tauto.
Qed.
(* End of proof of lem_surj_to_sig                                         *)

Lemma lem_inj_to_sig : forall f a b : E, fun_inj f a b -> fun_sig f a b.