proposition: Lemma mulidC m n (I : 'cV[R]_m) (J : 'cV[R]_n) : (I *i J :=: J *i I)%IS.
proof: Proof. by apply/eqidP; rewrite !subid_mulC. 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