proposition: Lemma rpredX n : {in S, forall u, u ^+ n \in S}.
proof: Proof. by move=> u Su; rewrite -(card_ord n) -prodr_const rpred_prod. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)