proposition: Lemma nbhs_entourage (x : M) A : entourage A -> nbhs x (to_set A x).
proof: Proof. by move=> ?; apply/nbhsP; 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