proposition: Lemma rowV0Pn m n (A : 'M_(m, n)) : reflect (exists2 v : 'rV_n, v <= A & v != 0)%MS (A != 0).
proof: Proof. rewrite -submx0; apply: (iffP idP) => [| [v svA]]; last first. by rewrite -submx0; apply: contra (submx_trans _). by case/row_subPn=> i; rewrite submx0; exists (row i A); rewrite ?row_sub. 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)