proposition: Lemma mul1mx m n (A : 'M_(m, n)) : 1%:M *m A = A.
proof: Proof. by rewrite -diag_const_mx mul_diag_mx; apply/matrixP => i j; rewrite !mxE mul1r. 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)