Ubuntu 18.04 に lxde をインストールできない

Ubuntu 18.04 に lxde をインストールできない

lubuntuのデスクトップ環境をインストールしようとしていますUbuntu 18.04.02が、次のエラーが発生します。

$ sudo apt install -y lubuntu-desktop
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 lubuntu-desktop : Depends: lubuntu-gtk-core but it is not going to be installed
                   Depends: lubuntu-gtk-desktop but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

これを解決する方法はありますか?

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