Installed Cyanogenmod 13 on Nexus 10, since Google ceased support with Android Lollipop 5.1, and tablet was running slower and slower. Unlocked device with no issue. Couldn’t get TWRP environment to install via adb, even after manually upgrading Android Platform Tools on Ubuntu to current version. Success came through installing Kingo Root from Google Play Store, and then TWRP Manager, which eased Cyanogenmod 13 for Manta and Gapps Pico installs after wiping memory. First try with Gapps Nano failed, so system partition is a constraint on the Nexus 10. Still preferring F-Droid installations over Google Play Store, for apps that don’t include commercials.