(************************************************************************)
(*         *      The Rocq Prover / The Rocq Development Team           *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
(************************************************************************)
Local Open Scope R_scope.
(*******************************************)
(*            Newton's Integral            *)
(*******************************************)
Definition Newton_integrable (f:R -> R) (a b:R) : Type :=
{ g:R -> R | antiderivative f g a b \/ antiderivative f g b a }.
Definition NewtonInt (f:R -> R) (a b:R) (pr:Newton_integrable f a b) : R :=
let (g,_) := pr in g b - g a.

(* If f is differentiable, then f' is Newton integrable (Tautology ?) *)
Lemma FTCN_step1 :
forall (f:Differential) (a b:R),
Newton_integrable (fun x:R => derive_pt f x (cond_diff f x)) a b.