proposition: Lemma discrete_closed (A : set X) : closed A.
proof: Proof. by rewrite -[A]setCK closedC; exact: discrete_open. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed