proposition: Lemma clopen_comp {T U : topologicalType} (f : T -> U) (A : set U) : clopen A -> continuous f -> clopen (f @^-1` A).
proof: Proof. by case=> ? ?; split; [ exact: open_comp | exact: closed_comp]. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed