proposition: Lemma col_flat_mx m n (A : 'M_(0,n)) (B : 'M_(m,n)) : col_mx A B = B.
proof: Proof. apply/matrixP=> i j; rewrite mxE; case: splitP => [|k H]; first by case. by congr fun_of_matrix; exact: val_inj. 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)