proposition: Lemma divring_closed_div : divring_closed -> sdivr_closed.
proof: Proof. case=> S1 SB Sdiv; split; rewrite ?zmod_closedN //. exact/subring_closedB/divring_closedBM. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)