Проблемы при переустановке KDE Plasma на Ubuntu 16.04

Я установил KDE Plasma 5.6 на Ubuntu 16.04, и все работало правильно.

Несколько дней назад я попытался установить более новую версию плазмы KDE (я пробовал упомянутую промежуточную версию ppa здесь и другие испытания) и каким-то образом сломал свой KDE.

Теперь я хотел бы переустановить KDE Plasma 5.6, поэтому попытался сначала удалить все следы KDE и установить его снова, в основном следуя командам, использовавшимся в прошлом:

$ sudo add-apt-repository ppa:kubuntu-ppa/backports
$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo apt-get install kubuntu-desktop

, но теперь я получить эту ошибку:

The following packages have unmet dependencies:
 kubuntu-desktop : Depends: breeze but it is not going to be installed
                   Depends: dolphin but it is not going to be installed
                   Depends: kde-cli-tools but it is not going to be installed
                   Depends: khelpcenter but it is not going to be installed
                   Depends: kinfocenter but it is not going to be installed
                   Depends: kwin
                   Depends: plasma-desktop but it is not going to be installed
                   Depends: sddm-theme-breeze but it is not going to be installed
                   Depends: systemsettings but it is not going to be installed
                   Recommends: akregator but it is not going to be installed
                   Recommends: apturl-kde but it is not going to be installed
                   Recommends: bluedevil but it is not going to be installed
                   Recommends: kaddressbook but it is not going to be installed
                   Recommends: kate but it is not going to be installed
                   Recommends: kde-config-sddm but it is not going to be installed
                   Recommends: kde-telepathy but it is not going to be installed
                   Recommends: kdeconnect-plasma but it is not going to be installed
                   Recommends: kmail but it is not going to be installed
                   Recommends: knotes but it is not going to be installed
                   Recommends: kontact but it is not going to be installed
                   Recommends: korganizer but it is not going to be installed
                   Recommends: kscreen but it is not going to be installed
                   Recommends: kwin-addons but it is not going to be installed
                   Recommends: milou but it is not going to be installed
                   Recommends: plasma-dataengines-addons but it is not going to be installed
                   Recommends: plasma-discover but it is not going to be installed
                   Recommends: plasma-nm but it is not going to be installed
                   Recommends: plasma-pa but it is not going to be installed
                   Recommends: plasma-runners-addons but it is not going to be installed
                   Recommends: plasma-wallpapers-addons but it is not going to be installed
                   Recommends: plasma-widgets-addons but it is not going to be installed
                   Recommends: print-manager but it is not going to be installed

Что я могу сделать? Большое спасибо Винченцо