proposition: Lemma locally_base_htrue : isfilter_htrue (neighborhood' x base).
proof: Proof. apply (pr2 (neighborhood_equiv _ _ _)). apply (pr2 (neighborhood_isOpen _)). - apply isOpen_htrue. - apply tt. Qed.
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.Topology.Filters UniMath.Algebra.Groups UniMath.Algebra.DivisionRig UniMath.Algebra.ConstructiveStructures