proposition: Lemma addid_congr m n p o (I: 'cV[R]_m) (J: 'cV[R]_n) (K: 'cV[R]_p) (L : 'cV_o) : (I <= K -> J <= L -> I +i J <= K +i L)%IS.
proof: Proof. case/subidP => X hX; case/subidP => Y hY; apply/subidP. exists (block_mx X 0 0 Y). by rewrite mul_block_col !mul0mx addr0 add0r hX hY. 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