fact: Definition filter_ex {T : Type} (F : set_system T) {FF : ProperFilter F} := filter_ex_subproof (filter_not_empty F).
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed