proposition: Lemma mul_dsub_mx m k n p (A : 'M_(m + k, n)) (B : 'M_(n, p)) : dsubmx A *m B = dsubmx (A *m B).
proof: Proof. by rewrite !dsubmxEsub mul_rowsub_mx. 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)