proposition: Lemma sub_kermx p m n (A : 'M_(m, n)) (B : 'M_(p, m)) : (B <= kermx A)%MS = (B *m A == 0).
proof: Proof. exact/sub_kermxP/eqP. 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)