Definition CV_radius (a : nat -> R) : Rbar :=
Lub_Rbar (CV_disk a).

(* Specifications: *)
Lemma CV_radius_ge_0 (a : nat -> R) :
Rbar_le (Finite 0) (CV_radius a).
Lemma CV_radius_bounded (a : nat -> R) :
is_lub_Rbar (fun r => exists M, forall n, Rabs (a n * r ^ n) <= M) (CV_radius a).