(** This file is part of the Coquelicot formalization of real analysis in Coq: http://coquelicot.saclay.inria.fr/  Copyright (C) 2011-2015 Sylvie Boldo #<br /># Copyright (C) 2011-2015 Catherine Lelay #<br /># Copyright (C) 2011-2015 Guillaume Melquiond  This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.  This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the COPYING file for more details. *)
(** This file describes defineitions and properties of continuity on [R] and on uniform spaces. It also contains many results about the limit of a real function (predicates [is_lim] and [ex_lim] and total function [Lim]). This limit may be either a real or an extended real. *)
(** * Limit of fonctions *)
(** ** Definition *)
Definition is_lim (f : R -> R) (x l : Rbar) :=
filterlim f (Rbar_locally' x) (Rbar_locally l).
Definition is_lim' (f : R -> R) (x l : Rbar) :=
match l with
| Finite l =>
forall eps : posreal, Rbar_locally' x (fun y => Rabs (f y - l) < eps)
| p_infty => forall M : R, Rbar_locally' x (fun y => M < f y)
| m_infty => forall M : R, Rbar_locally' x (fun y => f y < M)
end.
Definition ex_lim (f : R -> R) (x : Rbar) := exists l : Rbar, is_lim f x l.
Definition ex_finite_lim (f : R -> R) (x : Rbar) := exists l : R, is_lim f x l.
Definition Lim (f : R -> R) (x : Rbar) := Lim_seq (fun n => f (Rbar_loc_seq x n)).
(** Equivalence with standard library Reals *)
(** Composition *)
(** Uniqueness *)
(** ** Operations and order *)
(** Extensionality *)
(** Composition *)
(** Identity *)
(** Constant *)
(** *** Additive operators *)
(** Opposite *)
(** Addition *)
(** Subtraction *)
(** ** Multiplicative operators *)
(** Multiplicative inverse *)
(** Multiplication *)
(** Scalar multiplication *)
(** Division *)
(** Composition by linear functions *)
(** Continuity and limit *)
(** *** Order *)
(** ** Generalized intermediate value theorem *)

Lemma IVT_Rbar_decr (f : R -> R) (a b la lb : Rbar) (y : R) :
is_lim f a la -> is_lim f b lb
-> (forall (x : R), Rbar_lt a x -> Rbar_lt x b -> continuity_pt f x)
-> Rbar_lt a b
-> Rbar_lt lb y /\ Rbar_lt y la
-> {x : R | Rbar_lt a x /\ Rbar_lt x b /\ f x = y}.