proposition: Lemma discrete_open (A : set X) : open A.
proof: Proof. by rewrite openE => ? ?; rewrite /interior dsc; exact/principal_filterP. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed