(* End of proof of lem_rel_Comp_rel_sig                                    *)

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(* Reunion de relations                                                    *)
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Definition rel_union (r1 a1 b1 r2 a2 b2 : E) (rRel1 : rel_sig r1 a1 b1)
  (rRel2 : rel_sig r2 a2 b2) := union r1 r2.

Lemma lem_rel_union_dom : forall (r1 a1 b1 r2 a2 b2 : E) (rRel1 : rel_sig r1 a1 b1) (rRel2 : rel_sig r2 a2 b2), rdom (rel_union r1 a1 b1 r2 a2 b2 rRel1 rRel2) (union a1 a2) (union b1 b2) (lem_rel_union_rel_sig r1 a1 b1 r2 a2 b2 rRel1 rRel2) = union (rdom r1 a1 b1 rRel1) (rdom r2 a2 b2 rRel2).