proposition: Lemma nbhs_dnbhs {T : topologicalType} (x : T) : x^' `=>` nbhs x.
proof: Proof. exact: cvg_within. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed