proposition: Lemma mxsub_eq_colsub n' f g : f =1 id -> @mxsub _ n' f g =1 colsub g.
proof: Proof. by move=> f_id; apply: eq_mxsub. 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)