proposition: Lemma filtersubtype_htrue : isfilter_htrue filtersubtype.
proof: Proof. apply Himp with (2 := Htrue). intros x H _. exact H. Qed.
imports: UniMath.Foundations.Preamble UniMath.MoreFoundations.Tactics UniMath.Topology.Prelim UniMath.MoreFoundations.PartA