(** Definition of ps_atan's derivative *)
Definition Datan_seq := fun (x : R) (n : nat) => x ^ (2*n).

Lemma Ratan_CVU :
CVU (fun N x => sum_f_R0 (tg_alt (Ratan_seq x)) N)
ps_atan 0 (mkposreal 1 Rlt_0_1).