proposition: Lemma subset_closure (A : set T) : A `<=` closure A.
proof: Proof. by move=> p ??; exists p; split=> //; apply: nbhs_singleton. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed