proposition: Lemma subid_le0 m n (I : 'cV[R]_n) : (I <= (0 : 'cV_m))%IS = (I == 0).
proof: Proof. apply/subidP/eqP => [[D ->]|->]; first by rewrite mulmx0. by exists 0; rewrite mul0mx. 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