Totally remove Unity from Ubuntu 12.04 Precise

sudo apt-get install gdm gnome-shell synaptic deborphan

select "gdm"

Reboot the system to log and choose "Gnome"

removal of Unity in all its components:
sudo apt-get remove unity unity-2d unity-2d-common unity-2d-panel unity-2d-shell unity-2d-spread unity-asset-pool unity-common unity-lens-applications unity-lens-files unity-lens-music unity-lens-video unity-scope-musicstores unity-scope-video-remote unity-services indicator-messages indicator-status-provider-mc5 appmenu-qt appmenu-gtk appmenu-gtk3 lightdm unity-greeter overlay-scrollbar zeitgeist zeitgeist-core zeitgeist-datahub activity-log-manager-common activity-log-manager-control-center

sudo apt-get autoremove

sudo apt-get purge `deborphan`
sudo apt-get purge `deborphan`
sudo apt-get purge `deborphan`

sudo dpkg --purge `dpkg -l | egrep "^rc" | cut -d' ' -f3`

a clean Ubuntu 12.04 and distilled, with only Gnome Shell.
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