Definition Family := Ensemble (Ensemble T).Inductive FamilyUnion: Ensemble T :=
  | family_union_intro: forall (S:Ensemble T) (x:T),
    In F S -> In S x -> In FamilyUnion x.Inductive FamilyUnion: Ensemble T :=
  | family_union_intro: forall (S:Ensemble T) (x:T),
    In F S -> In S x -> In FamilyUnion x.Inductive FamilyIntersection: Ensemble T :=
  | family_intersection_intro: forall x:T,
    (forall S:Ensemble T, In F S -> In S x) ->
    In FamilyIntersection x.Inductive FamilyIntersection: Ensemble T :=
  | family_intersection_intro: forall x:T,
    (forall S:Ensemble T, In F S -> In S x) ->
    In FamilyIntersection x.

Lemma empty_family_intersection: FamilyIntersection (@Empty_set (Ensemble T)) = Full_set.