I'd like to enter a short alpha using the compose key: ᾰ. I tried using compose+U+α but this doesn't work. Neither does using b instead of U.
How can I enter the short alpha using the compose key?
U+1FB0 is not in the X.org standard compose map.
You can define your own compose map by creating a file
.XCompose in your home directory. See UTF8 math symbols & keyboard layout / input
for more details. Copy the default file from
/usr/share/X11/locale/en_US.UTF-8/Compose (the location may be different in different distributions) and a line like
<Multi_key> <a> <u> : U1fb0 # "ᾰ"
Alternatively, you can try another input method (Xim, Gtkim, Scim, …). I don't know which common input method has ᾰ by default or can easily be customized.