Section Minus.
Context {K : AbsRing} {V : NormedModule K}.
End Minus.
(** ** Multiplicative operators *)
(** Multiplication of functions *)

Lemma is_derive_scal :
forall (f : R -> R) (x k df : R),
is_derive f x df ->
is_derive (fun x : R => k * f x) x (k * df).