Definition Bessel1 (n : nat) (x : R) :=
  (x/2)^n * PSeries (Bessel1_seq n) ((x/2)^2).

Lemma Bessel1_uniqueness (a : nat -> R) (n : nat) : (Rbar_lt 0 (CV_radius a)) -> (forall x : R, x^2 * Derive_n (PSeries a) 2 x + x * Derive (PSeries a) x + (x^2 - (INR n)^2) * PSeries a x = 0) -> {b : R | forall x, PSeries a x = b * Bessel1 n x}.