proposition: Lemma mulmxDr m n p (A : 'M_(m, n)) (B1 B2 : 'M_(n, p)) : A *m (B1 + B2) = A *m B1 + A *m B2.
proof: Proof. apply/matrixP=> i k; rewrite !mxE -big_split /=. by apply: eq_bigr => j _; rewrite mxE mulrDr. 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)