proposition: Lemma rpredXN n : {in S, forall x, x ^- n \in S}.
proof: Proof. by move=> x Sx; rewrite /= rpredV rpredX. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)