ewrite exprS derivM {}IHn (mulrC p) mulrnAl -mulrA -exprSr mulrS; case n.
Qed.=1 id}.
Proof. by rewrite /poly_inv => p /negbTE/= ->. Qed.

Definition poly_comUnitMixin :=ComUnitRingMixin poly_mulVp poly_intro_unit poly_inv_out.

Canonical poly_unitRingType :=Eval hnf in [comUnitRingType of polynomial R].

Canonical poly_idomainType :=