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(* Axiome des parties                                                      *)
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Parameter parties : E -> E.Axiom
  axs_parties :
    forall v0 v2 : E,
    In v2 (parties v0) <-> (forall v3 : E, In v3 v2 -> In v3 v0).

(* Specifications: *)
Lemma lem_reunion_parties : forall x : E, reunion (parties x) = x.