proposition: Lemma diag_mx_is_linear n : linear (@diag_mx R n).
proof: Proof. by move=> a A B; apply/matrixP=> i j; rewrite !mxE mulrnAr mulrnDl. 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)