(* 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_prop : forall (r1 a1 b1 r2 a2 b2 : E) (rRel1 : rel_sig r1 a1 b1) (rRel2 : rel_sig r2 a2 b2) (c : E), In c (rel_union r1 a1 b1 r2 a2 b2 rRel1 rRel2) <-> In c r1 \/ In c r2.