proposition: Lemma gring_mxA a b : gring_mx rG (a *m gring_mx aG b) = gring_mx rG a *m gring_mx rG b.
proof: Proof. by rewrite -(gring_op_mx a) -gring_opJ gring_opE gring_row_mul gring_mxK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div choice fintype tuple finfun bigop prime) mathcomp(ssralg poly polydiv finset fingroup morphism) mathcomp(perm automorphism quotient finalg action zmodp) mathcomp(commutator cyclic center pgroup matrix mxalgebra) mathcomp(mxpoly)