proposition: Lemma nbhs_singleton (p : T) (A : set T) : nbhs p A -> A p.
proof: Proof. by rewrite nbhsE => - [? [_ ?]]; 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