proposition: Lemma subring_closed_semi : subring_closed -> semiring_closed S.
proof: Proof. by move=> ringS; split; [apply/zmod_closedD/subring_closedB | case: ringS]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)