proposition: Lemma isOpen_union : ∏ P : (T → hProp) → hProp, (∏ A : T → hProp, P A → isOpen A) → isOpen (union P).
proof: Proof. apply (pr1 (pr2 (pr2 T))). Qed.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.Topology.Filters UniMath.Algebra.Groups UniMath.Algebra.DivisionRig UniMath.Algebra.ConstructiveStructures