proposition: Lemma open_nbhsE (p : T) (A : set T) : open_nbhs p A = (open A /\ nbhs p A).
proof: Proof. by rewrite nbhsE propeqE; split=> [[? ?]|[? [B [? ?] BA]]]; split => //; [exists A | exact: BA]. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed