Recover Nexus 9 lost in a boot loop

 My old Nexus 9 tablet was caught in a boot loop: it would boot up, then freeze, reboot, freeze, ... until the battery was exhausted. The instructions at stackexchange helped a lot. Here is a summary of what I did:

1. Download the latest OTA file from Google's Developper site. This is a zip file. Do not uncompress it.
2. Reboot in Recovery Mode. For the Nexus 9, press the power and volume up buttons until a menu appears. Choose Recovery Mode.
3. Once in Recovery Mode (recognisable by its Android mascot laying on its back), quickly press the Power Button and Volume Up to enter a hidden menu.
4. Choose "Apply update from adb"
5. On the computer, run "adb sideload <ota_file.zip>"
6. After the update is done, choose "Reboot system now"