proposition: Lemma diag_mx_is_additive n : additive (@diag_mx V n).
proof: Proof. by move=>A B; apply/matrixP=>i j; rewrite !mxE mulrnBl. 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)