proposition: Lemma capmx_idPl n m1 m2 (A : 'M_(m1, n)) (B : 'M_(m2, n)) : reflect (A :&: B :=: A)%MS (A <= B)%MS.
proof: Proof. by rewrite capmxC; apply: capmx_idPr. 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)