proposition: Lemma closeEonbhs x : close x = [set y | open_nbhs x `#` open_nbhs y].
proof: Proof. by rewrite closeEnbhs; under eq_fun do rewrite -meets_openl -meets_openr. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed