(** Difference of functions *)
Section Minus.
Context {K : AbsRing} {V : NormedModule K}.

(* Specifications: *)
Lemma is_derive_minus :
forall (f g : K -> V) (x : K) (df dg : V),
is_derive f x df ->
is_derive g x dg ->
is_derive (fun x => minus (f x) (g x)) x (minus df dg).
Lemma ex_derive_minus :
forall (f g : K -> V) (x : K),
ex_derive f x -> ex_derive g x ->
ex_derive (fun x => minus (f x) (g x)) x.