End Derive.
(** * Definitions on [R] *)
Definition Derive (f : R -> R) (x : R) := real (Lim (fun h => (f (x+h) - f x)/h) 0).

(* Specifications: *)
Lemma is_derive_Reals (f : R -> R) (x l : R) :
is_derive f x l <-> derivable_pt_lim f x l.