End Extensionality.

(* Specifications: *)
Lemma PSeries_ext (a b : nat -> R) (x : R) :
(forall n, a n = b n) -> PSeries a x = PSeries b x.
Lemma Derive_ext_loc :
forall f g x,
locally x (fun t => f t = g t) ->
Derive f x = Derive g x.
Lemma Derive_ext :
forall f g x,
(forall t, f t = g t) ->
Derive f x = Derive g x.