(** 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)).

Lemma Lim_minus (f g : R -> R) (x : Rbar) : ex_lim f x -> ex_lim g x -> ex_Rbar_minus (Lim f x) (Lim g x) -> Lim (fun y => f y - g y) x = Rbar_minus (Lim f x) (Lim g x).