(** ** Convergence criteria *)
(** D'Alembert criterion for power series *)

Lemma CV_radius_finite_DAlembert (a : nat -> R) (l : R) :
(forall n:nat, a n <> 0) -> 0 < l ->
is_lim_seq (fun n:nat => Rabs (a (S n) / a n)) l ->
CV_radius a = Finite (/l).