proposition: Lemma mulmxDl m n p (A1 A2 : 'M_(m, n)) (B : 'M_(n, p)) : (A1 + A2) *m B = A1 *m B + A2 *m B.
proof: Proof. apply/matrixP=> i k; rewrite !mxE -big_split /=. by apply: eq_bigr => j _; rewrite !mxE -mulrDl. 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)