proposition: Lemma add_addil m n p (I: 'cV[R]_m) (J: 'cV[R]_n) (K: 'cV[R]_p) : (J :=: K)%IS -> (I +i J :=: I +i K)%IS.
proof: Proof. by move=> eqJK; apply/eqidP; rewrite ?sub_addidl ?eqJK. 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