proposition: Lemma union_disj_d : forall (x : Elt) (a b : Ensf), dans x b -> dans (injdroite x) (union_disj a b).
proof: Proof. intros. unfold union_disj in |- *. apply union_d. apply dans_map_inv. auto. Qed.
imports: Ensf_types Ensf_dans Ensf_union Ensf_couple Ensf_inclus Ensf_map