proposition: Lemma exprMn n : {morph (fun x => x ^+ n) : x y / x * y}.
proof: Proof. by move=> x y; exact/exprMn_comm/mulrC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)