proposition: Lemma addid_addA m n p (I: 'cV[R]_m) (J: 'cV[R]_n) (K: 'cV[R]_p): (I +i (J +i K) :=: (I +i J) +i K)%IS.
proof: Proof. by apply/eqidP; rewrite subid_addAl subid_addAr. 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