~$ sudo ppa-purge ppa:elementary-os/stableUpdating packages lists
W: The repository 'http://ppa.launchpad.net/versable/elementary-update/ubuntu xenial Release' does not have a Release file.
E: Impossibile recuperare http://ppa.launchpad.net/versable/elementary-update/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found
E: Impossibile scaricare alcuni file di indice: saranno ignorati o verranno usati quelli vecchi.
Warning:  apt-get update failed for some reason