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

Lemma Derive_inv (f : R -> R) (x : R) :
ex_derive f x -> f x <> 0
-> Derive (fun y => / f y) x = - Derive f x / (f x) ^ 2.