proposition: Lemma diag_mx_is_semi_additive n : semi_additive (@diag_mx n).
proof: Proof. by split=> [|A B]; apply/matrixP => i j; rewrite !mxE ?mul0rn// 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)