proposition: Lemma rV_subP m1 m2 n (A : 'M_(m1, n)) (B : 'M_(m2, n)) : reflect (forall v : 'rV_n, v <= A -> v <= B)%MS (A <= B)%MS.
proof: Proof. apply: (iffP idP) => [sAB v Av | sAB]; first exact: submx_trans sAB. by apply/row_subP=> i; rewrite sAB ?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)