proposition: Lemma commuteM x y z : commute x y -> commute x z -> commute x (y * z).
proof: Proof. by move=> cxy cxz; rewrite /commute -mulgA -cxz !mulgA cxy. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)