proposition: Lemma mul_xcol m n p j1 j2 (A : 'M_(m, n)) (B : 'M_(n, p)) : xcol j1 j2 A *m B = A *m xrow j1 j2 B.
proof: Proof. by rewrite mul_col_perm tpermV. 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)