proposition: Lemma closure0 : closure set0 = set0 :> set T.
proof: Proof. rewrite predeqE => x; split => // /(_ _ (filter_nbhsT _))/set0P. by rewrite set0I eqxx. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed