Section StrongTopology.
Variable A:Type.
Variable X:forall a:A, TopologicalSpace.
Variable Y:Type.
Variable f:forall a:A, point_set (X a) -> Y.
Definition strong_open (S:Ensemble Y) : Prop :=
forall a:A, open (inverse_image (f a) S).
Definition StrongTopology : TopologicalSpace.
refine (Build_TopologicalSpace Y strong_open _ _ _).
- intros.
red; intro.
assert (inverse_image (f a) (FamilyUnion F) =
IndexedUnion (fun U:{ U:Ensemble Y | In F U } =>
inverse_image (f a) (proj1_sig U))).
{ apply Extensionality_Ensembles; red; split; red; intros.
- destruct H0.
inversion H0.
exists (exist _ S H1).
constructor.
exact H2.
- destruct H0. destruct H0.
destruct a0 as [U].
constructor.
exists U; trivial.
}
rewrite H0.
apply open_indexed_union.
intros.
destruct a0 as [U].
simpl.
apply H; trivial.
- intros.
red; intro.
rewrite inverse_image_intersection.
apply open_intersection2; (apply H || apply H0).
- red; intro.
rewrite inverse_image_full.
apply open_full.
Defined.

Lemma strong_topology_makes_continuous_funcs:
forall a:A, continuous (f a) (Y:=StrongTopology).