proposition: Lemma clopenC {T} (A B : set T) : clopen A -> clopen (~`A).
proof: Proof. by case=> ? ?; split;[exact: closed_openC | exact: open_closedC ]. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed