proposition: Remark subid_memberP m n (I : 'cV[R]_m) (J : 'cV[R]_n) : reflect (forall x, member x I -> member x J) (I <= J)%IS.
proof: Proof. apply: (iffP idP); first by move=> leIJ i; rewrite !memberE => /subid_trans ->. move=> HIJ; apply/subid_colP => i. by move: (HIJ (I i 0)); rewrite !memberE; apply. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype perm choice fingroup) mathcomp(matrix bigop zmodp mxalgebra poly) ssrcomplements