diff --git a/docs/nixos-with-flakes/modularize-the-configuration.md b/docs/nixos-with-flakes/modularize-the-configuration.md
index 83c3e86..e32cf74 100644
--- a/docs/nixos-with-flakes/modularize-the-configuration.md
+++ b/docs/nixos-with-flakes/modularize-the-configuration.md
@@ -83,96 +83,6 @@ For example, [ryan4yin/nix-config/v0.0.2](https://github.com/ryan4yin/nix-config
 └── wallpaper.jpg    # wallpaper
 ```
 
-For more details, see [ryan4yin/nix-config/v0.0.2](https://github.com/ryan4yin/nix-config/tree/v0.0.2).
-
-## `lib.mkOverride`, `lib.mkDefault`, and `lib.mkForce`
-
-Some people use `lib.mkDefault` and `lib.mkForce` to define values in Nix files. As their names suggest, `lib.mkDefault` and `lib.mkForce` are used to set default values or force values of options.
-
-You can read the source code of `lib.mkDefault` and `lib.mkForce` by running `nix repl -f '<nixpkgs>'` and then entering `:e lib.mkDefault`. To learn the basic usage of `nix repl`, type `:?` to see the help information.
-
-Here's the source code:
-
-```nix
-  # ......
-
-  mkOverride = priority: content:
-    { _type = "override";
-      inherit priority content;
-    };
-
-  mkOptionDefault = mkOverride 1500; # priority of option defaults
-  mkDefault = mkOverride 1000; # used in config sections of non-user modules to set a default
-  mkImageMediaOverride = mkOverride 60; # image media profiles can be derived by inclusion into host config, hence needing to override host config, but do allow user to mkForce
-  mkForce = mkOverride 50;
-  mkVMOverride = mkOverride 10; # used by ‘nixos-rebuild build-vm’
-
-  # ......
-```
-
-`lib.mkDefault` is used to set default values of options with a priority of 1000 internally, while `lib.mkForce` is used to force values of options with a priority of 50 internally. If you set a value of an option directly, it will be set with a default priority of 1000 (the same as `lib.mkDefault`).
-
-The lower the `priority` value, the higher the actual priority. Therefore, `lib.mkForce` has a higher priority than `lib.mkDefault`. If you define multiple values with the same priority, Nix will throw an error.
-
-These functions are useful for modularizing the configuration. You can set default values in a low-level module (base module) and force values in a high-level module.
-
-As an example, in my configuration <https://github.com/ryan4yin/nix-config/blob/main/modules/nixos/core-server.nix#L30>, I define default values here:
-
-```nix
-{ lib, pkgs, ... }:
-
-{
-  # ......
-
-  nixpkgs.config.allowUnfree = lib.mkDefault false;
-
-  # ......
-}
-```
-
-And for my dekstop machine, I force the values to another value in <https://github.com/ryan4yin/nix-config/blob/main/modules/nixos/core-desktop.nix#L15>:
-
-```nix
-{ lib, pkgs, ... }:
-
-{
-  # import the base module
-  imports = [
-    ./core-server.nix
-  ];
-
-  # override the default value defined in the base module
-  nixpkgs.config.allowUnfree = lib.mkForce true;
-
-  # ......
-}
-```
-
-## `lib.mkOrder`, `lib.mkBefore`, and `lib.mkAfter`
-
-`lib.mkBefore` and `lib.mkAfter` are used to set the merge order of **list-type options**. Like `lib.mkDefault` and `lib.mkForce`, they're also useful for modularizing the configuration.
-
-As I mentioned earlier, if you define multiple values with the same **override priority**, Nix will throw an error. However, with `lib.mkOrder`, `lib.mkBefore`, or `lib.mkAfter`, you can define multiple values with the same override priority, and they will be merged in the order you defined.
-
-To take a look at the source code of `lib.mkBefore`, run `nix repl -f '<nixpkgs>'` and then enter `:e lib.mkBefore`. To learn the basic usage of `nix repl`, type `:?` to see the help information:
-
-```nix
-  # ......
-
-  mkOrder = priority: content:
-    { _type = "order";
-      inherit priority content;
-    };
-
-  mkBefore = mkOrder 500;
-  mkAfter = mkOrder 1500;
-
-  # The default priority for things that don't have a priority specified.
-  defaultPriority = 100;
-
-  # ......
-```
-
 For more details, you can refer to the [ryan4yin/nix-config/v0.0.2](https://github.com/ryan4yin/nix-config/tree/v0.0.2) repository.
 
 ## `lib.mkOverride`, `lib.mkDefault`, and `lib.mkForce`