proposition: Lemma mulrnDl n : {morph (fun x => x *+ n) : x y / x + y}.
proof: Proof. move=> x y; elim: n => [|n IHn]; rewrite ?addr0 // !mulrS. by rewrite addrCA -!addrA -IHn -addrCA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)