proposition: Lemma mul_scalar_mx m n a (A : 'M_(m, n)) : a%:M *m A = a *: A.
proof: Proof. by rewrite -diag_const_mx mul_diag_mx; apply/matrixP=> i j; rewrite !mxE. 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)