fact: Structure pfilter_on T := PFilterPack { pfilter :> (T -> Prop) -> Prop; _ : ProperFilter pfilter }.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed