proposition: Lemma mulmx_free_eq0 m n p (A : 'M_(m, n)) (B : 'M_(n, p)) : row_free B -> (A *m B == 0) = (A == 0).
proof: Proof. by rewrite -sub_kermx -kermx_eq0 => /eqP->; rewrite submx0. 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 finalg zmodp matrix)