proposition: Lemma subid_trans n m p (J : 'cV[R]_n) (I : 'cV[R]_m) (K : 'cV[R]_p) : (I <= J)%IS -> (J <= K)%IS -> (I <= K)%IS.
proof: Proof. by move=> /subidP [I' ->] /subidP [J' ->]; rewrite mulmxA subidMl. 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