proposition: Lemma mul_col_mx m1 m2 n p (Au : 'M_(m1, n)) (Ad : 'M_(m2, n)) (B : 'M_(n, p)) : col_mx Au Ad *m B = col_mx (Au *m B) (Ad *m B).
proof: Proof. apply/matrixP=> i k; rewrite !mxE. by case defi: (split i) => /[!mxE]; under eq_bigr do rewrite mxE defi. 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)