Section NullDerivative.
Context {V : NormedModule R_AbsRing}.
End NullDerivative.
(** * 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.
(** Extensionality *)
(** Constant function *)
(** ** Operations *)
(** *** Additive operators *)
(** Opposite *)
(** Addition of functions *)
(** Subtraction of functions *)

Lemma is_derive_n_minus (f g : R -> R) (n : nat) (x lf lg : R) :
locally x (fun y => forall k, (k <= n)%nat -> ex_derive_n f k y) ->
locally x (fun y => forall k, (k <= n)%nat -> ex_derive_n g k y) ->
is_derive_n f n x lf -> is_derive_n g n x lg ->
is_derive_n (fun x => f x - g x) n x (lf - lg).