proposition: Lemma withinET {F} {FF : Filter F} : within setT F = F.
proof: Proof. rewrite eqEsubset /within; split => X //=; by apply: filter_app => //=; apply: nearW => // x; apply. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed