proposition: Lemma rpred_div : {in S &, forall x y, x / y \in S}.
proof: Proof. by move=> x y Sx Sy; rewrite /= rpredM ?rpredV. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)