proposition: Lemma nz_row_sub m n (A : 'M_(m, n)) : (nz_row A <= A)%MS.
proof: Proof. by rewrite /nz_row; case: pickP => [i|] _; rewrite ?row_sub ?sub0mx. 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)