proposition: Lemma open_nbhs_nbhs (p : T) (A : set T) : open_nbhs p A -> nbhs p A.
proof: Proof. by rewrite nbhsE => p_A; exists A. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed