proposition: Lemma mulmx_lsub m n p k (A : 'M_(m, n)) (B : 'M_(n, p + k)) : A *m lsubmx B = lsubmx (A *m B).
proof: Proof. by rewrite !lsubmxEsub mulmx_colsub. 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)