proposition: Lemma rpredB : {in S &, forall u v, u - v \in S}.
proof: Proof. by move=> u v Su Sv; rewrite /= rpredD ?rpredN. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)