proposition: Lemma isaprop_isfilter_notempty : isaprop isfilter_notempty.
proof: Proof. apply impred_isaprop ; intro A. apply isapropimpl. apply propproperty. Qed.
imports: UniMath.Foundations.Preamble UniMath.MoreFoundations.Tactics UniMath.Topology.Prelim UniMath.MoreFoundations.PartA