proposition: Lemma col_mx0 m1 m2 n : col_mx 0 0 = 0 :> 'M_(m1 + m2, n).
proof: Proof. exact: col_mx_const. 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)