fact: Definition isSetOfOpen_union := ∏ P : (X → hProp) → hProp, (∏ A : X → hProp, P A → O A) → O (union P).
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.Topology.Filters UniMath.Algebra.Groups UniMath.Algebra.DivisionRig UniMath.Algebra.ConstructiveStructures