proposition: Lemma filterbase_htrue : isfilter_htrue filterbase.
proof: Proof. revert Hempty. apply hinhfun. intros A. exists (pr1 A). split. - apply (pr2 A). - intros. exact tt. Qed.
imports: UniMath.Foundations.Preamble UniMath.MoreFoundations.Tactics UniMath.Topology.Prelim UniMath.MoreFoundations.PartA