How can one add custom Compose-key sequences? I have googled quite a bit, but could not find an explanation. In particular, I would like to have:
<Compose> + <Z> + <Z> = ℤ # Blackboard bold Z (set of integers)
In particular, I tried copying the file /usr/share/X11/locale/en_US.UTF-8/Compose to ~/.XCompose, and mimicked its syntax. However, this did not seem to work.
Best Answer
See @Gilles' answer.
Original answer:
You may need to log out and in again, since your personal configuration files are read when logging in.
(There may also be some way to activate it without logging out and in again, but I'm not familiar with this specific configuration file.)