proposition: Lemma scalemxAl m n p a (A : 'M_(m, n)) (B : 'M_(n, p)) : a *: (A *m B) = (a *: A) *m B.
proof: Proof. apply/matrixP=> i k; rewrite !mxE big_distrr /=. by apply: eq_bigr => j _; rewrite mulrA mxE. 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)