proposition: Lemma colsub_comp m n n2 n3 (g : 'I_n2 -> 'I_n) (g' : 'I_n3 -> 'I_n2) (A : 'M_(m, n)) : colsub (g \o g') A = colsub g' (colsub g A).
proof: Proof. exact: mxsub_comp. 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)