proposition: Lemma memmx_subP m1 m2 n (R1 : 'A_(m1, n)) (R2 : 'A_(m2, n)) : reflect (forall A, A \in R1 -> A \in R2) (R1 <= R2)%MS.
proof: Proof. apply: (iffP idP) => [sR12 A R1_A | sR12]; first exact: submx_trans sR12. by apply/rV_subP=> vA; rewrite -(vec_mxK vA); apply: sR12. 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)