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

Lemma is_derive_inv (f : R -> R) (x l : R) :
is_derive f x l -> f x <> 0
-> is_derive (fun y : R => / f y) x (-l/(f x)^2).