proposition: Lemma subid_castmxr m n p (I : 'cV[R]_m) (J : 'cV[R]_n) (h : n = p): (I <= (castmx (h,erefl _) J))%IS = (I <= J)%IS.
proof: Proof. by case: _ / h. 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