proposition: Lemma natrM m n : (m * n)%:R = m%:R * n%:R :> R.
proof: Proof. by rewrite mulrnA mulr_natr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)