Section OneMatrix.
Variable A : 'M[R]_n.
Definition horner_mx := horner_morph (comm_mx_scalar^~ A).
Canonical horner_mx_additive := [additive of horner_mx].
Canonical horner_mx_rmorphism := [rmorphism of horner_mx].

Lemma horner_mx_C a : horner_mx a%:P = a%:M.