proposition: Lemma scalerMnl a v n : a *: v *+ n = (a *+ n) *: v.
proof: Proof. elim: n => [|n IHn]; first by rewrite !mulr0n scale0r. by rewrite !mulrSr IHn scalerDl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)