Section is_derive_mult.
Context {K : AbsRing}.
End is_derive_mult.
(** * Exponential function *)
(** Definition *)
(** Limits *)
(** Integral *)
(** * Natural logarithm *)
(** * Unnormalized sinc *)
(** * ArcTan *)

Lemma CV_radius_atan : CV_radius (fun n => (-1)^n / (INR (S (n + n)))) = 1.
Lemma atan_Reals (x : R) : Rabs x < 1
-> atan x = x * PSeries (fun n => (-1)^n / (INR (S (n + n)))) (x ^ 2).