Definition IndexedFamily := A -> Ensemble T.Inductive IndexedUnion : Ensemble T :=
  | indexed_union_intro: forall (a:A) (x:T),
    In (F a) x -> In IndexedUnion x.Inductive IndexedUnion : Ensemble T :=
  | indexed_union_intro: forall (a:A) (x:T),
    In (F a) x -> In IndexedUnion x.Inductive IndexedIntersection : Ensemble T :=
  | indexed_intersection_intro: forall (x:T),
    (forall a:A, In (F a) x) -> In IndexedIntersection x.Inductive IndexedIntersection : Ensemble T :=
  | indexed_intersection_intro: forall (x:T),
    (forall a:A, In (F a) x) -> In IndexedIntersection x.

Lemma sub_indexed_union: forall {A B T:Type} (f:A->B) (F:IndexedFamily B T), let subF := (fun a:A => F (f a)) in Included (IndexedUnion subF) (IndexedUnion F).