How to create lowercase pi (“π”) with compose key?

as others remark, there are no standard compose rules in X for π, so if you want to use compose to make the π symbol (as I just did), you could:

• install uim
• create ~/.XCompose
• put there the rules you need
• do not forget to start the file with include "%L"

mine looks like this:

include "%L"

<Multi_key> <l> <l>                 : "ℓ"   U2113     # litre symbol
<Multi_key> <p> <i>                 : "π"   U03C0     # GREEK SMALL LETTER PI

this works on Debian. it does affect the way Ctrl-Shift-u works.

The X11 compose list is typically under /usr/share/X11/locale/ (this location may vary between distributions though), but the Compose file is not necessarily in the directory named after your LC_CTYPE setting. There is a stage of translation of locale names via the file /usr/share/X11/locale/compose.dir. This translation allows many locales to share the same compose file. (Symbolic links would have been another way, but a text file is easier to distribute and works on platforms that don't have symbolic links — X11 exists outside of Unix.) Most locales that use the UTF-8 encoding for a language written in the Latin alphabet use the compose file for en_US.UTF-8, located in en_US.UTF-8/Compose.

In en_US.UTF-8/Compose, the only way to generate U03C0 (GREEK SMALL LETTER PI) is <dead_greek> <p>. There is no <Multi_key> (Compose) sequence. Among the keyboard layouts distributed with X.org, the only one that defines a dead_greek key is the BÉPO layout (a French analog of DVORAK). So there's no way to type π using the Compose key with the default configuration. And the default UK layout doesn't include a way to type π, not even in an XKB variant (a US Mac layout (us(mac)) will give you π on AltGr+P however).

As far as I can tell, there's never been a standard Compose sequence to insert π on Xorg. If you remember one, you might have been an input method other than X11's built-in mechanism.

This isn't super convenient, but it works:

If you look in your Compose file for the 'pi' symbol:

% grep -i greek /usr/share/X11/locale/en_US.UTF-8/Compose | grep -i 'letter pi'
<dead_greek> <P>            : "Π"   U03A0    # GREEK CAPITAL LETTER PI
<dead_greek> <p>            : "π"   U03C0    # GREEK SMALL LETTER PI

You see that the combination for lowercase π is U03C0

So if you press ControlShiftu and then type in 03c0 Space, you are left with a π symbol.

The other way that should work is to define a key with xmodmap, but I have had problems with some applications not responding to that.