(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** *   Metric space           *)
(*******************************)

(*********)
Record Metric_Space : Type :=
  {Base : Type;
    dist : Base -> Base -> R;
    dist_pos : forall x y:Base, dist x y >= 0;
    dist_sym : forall x y:Base, dist x y = dist y x;
    dist_refl : forall x y:Base, dist x y = 0 <-> x = y;
    dist_tri : forall x y z:Base, dist x y <= dist x z + dist z y}.(*******************************)
(** ** Limit in Metric space   *)
(*******************************)

(*********)
Definition limit_in (X X':Metric_Space) (f:Base X -> Base X')
  (D:Base X -> Prop) (x0:Base X) (l:Base X') :=
  forall eps:R,
    eps > 0 ->
    exists alp : R,
      alp > 0 /\
      (forall x:Base X, D x /\ (dist X) x x0 < alp -> (dist X') (f x) l < eps).(*******************************)
(** **  R is a metric space    *)
(*******************************)

(*********)
Definition R_met : Metric_Space :=
  Build_Metric_Space R Rdist Rdist_pos Rdist_sym Rdist_refl Rdist_tri.(*******************************)
(** *      Limit 1 arg         *)
(*******************************)
(*********)
Definition Dgf (Df Dg:R -> Prop) (f:R -> R) (x:R) := Df x /\ Dg (f x).(*********)
Definition limit1_in (f:R -> R) (D:R -> Prop) (l x0:R) : Prop :=
  limit_in R_met R_met f D x0 l.

Lemma limit_mul : forall (f g:R -> R) (D:R -> Prop) (l l' x0:R), limit1_in f D l x0 -> limit1_in g D l' x0 -> limit1_in (fun x:R => f x * g x) D (l * l') x0.