(** * Iterated differential *)

(** ** Definition *)

Fixpoint Derive_n (f : R -> R) (n : nat) x :=
  match n with
    | O => f x
    | S n => Derive (Derive_n f n) x
  end.Definition ex_derive_n f n x :=
  match n with
  | O => True
  | S n => ex_derive (Derive_n f n) x
  end.Definition is_derive_n f n x l :=
  match n with
  | O => f x = l
  | S n => is_derive (Derive_n f n) x l
  end.

Lemma ex_derive_n_comp_scal (f : R -> R) (a : R) (n : nat) (x : R) : locally (a * x) (fun x => forall k, (k <= n)%nat -> ex_derive_n f k x) -> ex_derive_n (fun y => f (a * y)) n x.