Identity Coercion type_poly_of : poly_of >-> polynomial.
Definition coefp_head h i (p : poly_of (Phant R)) := let: tt := h in p`_i.
End Polynomial.
(* We need to break off the section here to let the Bind Scope directives     *)
(* take effect.                                                               *)
Bind Scope ring_scope with poly_of.
Bind Scope ring_scope with polynomial.
Arguments polyseq {R} p%R.
Arguments poly_inj {R} [p1%R p2%R] : rename.
Arguments coefp_head {R} h i%N p%R.
Notation "{ 'poly' T }" := (poly_of (Phant T)).
Notation coefp i := (coefp_head tt i).
Definition poly_countMixin (R : countRingType) :=
[countMixin of polynomial R by <:].
Canonical polynomial_countType R := CountType _ (poly_countMixin R).
Canonical poly_countType (R : countRingType) := [countType of {poly R}].
Section PolynomialTheory.
Variable R : ringType.
Implicit Types (a b c x y z : R) (p q r d : {poly R}).
Canonical poly_subType := Eval hnf in [subType of {poly R}].
Canonical poly_eqType := Eval hnf in [eqType of {poly R}].
Canonical poly_choiceType := Eval hnf in [choiceType of {poly R}].
Definition lead_coef p := p`_(size p).-1.

Lemma lead_coefE p : lead_coef p = p`_(size p).-1. Proof. by []. Qed.
Definition poly_nil := @Polynomial R [::] (oner_neq0 R).