proposition: Lemma cvg_within {F} {FF : Filter F} D : within D F --> F.
proof: Proof. by move=> P; apply: filterS. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed