proposition: Lemma scalar_mxM n a b : (a * b)%:M = a%:M *m b%:M :> 'M_n.
proof: Proof. rewrite -[in RHS]diag_const_mx mul_diag_mx. by apply/matrixP => i j; rewrite !mxE mulrnAr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)