(* End of proof of lem_rId_dom                                             *)

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(* L'image de l'identite est a                                             *)
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(*
Lemma lem_rId_Img :
  (a:E)(rImg (rId a) a a (lem_rId_rel_sig a))=a
.
*)
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(* Complementaire d'une relation                                           *)
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Definition rel_Comp (r a b : E) (rRel : rel_sig r a b) :=
  Comp (cartesien a b) r.

Lemma lem_rel_Comp_rel_sig : forall (r a b : E) (rRel : rel_sig r a b), rel_sig (rel_Comp r a b rRel) a b.