X Compose

Users of the X.Org Server have also the possibility to use XCompose for multi-key input sequences and (among other things) entering Unicode characters e.g., "Compose+'+e" for or "Compose+*+a" for α. This method has the advantage to be independent of the user's editors or terminals emulators. Furthermore, the sequence keys can easily be customized. Here is a possible configuration.

Specify your compose key in the default keyboard layout, by setting the XKBOPTIONS variable (a semicolon-separated list of option components). E.g., On debian, add the following line to your /etc/default/keyboard if you want the Left Windows Key to be your compose key:

  XKBOPTIONS="compose:lwin"

If you do not have the superuser privileges or do not want to set the variable globally, you can also add the following line to your ~/.xinitrc or ~/.xprofile:

  setxkbmap -option "compose:lwin"

You can now set your own mappings in the ~/.XCompose file. If the pre-defined mappings (include "%S/en_US.UTF-8/Compose") are not enough, here is a comprehensive example. The syntax of these mappings is rather intuitive, and it is easy to extend your ~/.XCompose to your own needs e.g.,

 <Multi_key> <b> <n> : "ℕ" U2115 # MATHBB N
 <Multi_key> <b> <z> : "ℤ" U2124 # MATHBB Z

Some GTK and Qt applications (e.g., Firefox or Konqueror) try to redefine their own multi-key input sequences. To make them use your ~/.XCompose instead, add the following lines to your initialization profile (~/.bash_profile, ~/.profile, depending on your shell and display manager):

  export GTK_IM_MODULE=xim
  export QT_IM_MODULE=xim

Sample XCompose configuration file

It is actually possible to use XCompose without the compose key. Below is a setup which utilizes shortcuts similar to LaTeX, i.e. typing \forall inserts . Note that to insert \ you have to type \\ (the author of the file below is unsure how exactly this works, see line 3). Note that it is problematic if you have a shortcut which is a prefix of another shortcut in this case, you won't be able to insert the prefix shortcut. There is a workaround which involves appending <space> to your prefix shortcut, e.g. you type \top to insert and \to to insert (note the spaces after). include "%L" includes your default XCompose configuration file (on Arch Linux, this is /usr/share/X11/locale/en_US.UTF-8/Compose when using the specified keyboard layout).

The Wiki does not like Unicode in preformatted texts, making me link to it instead: https://github.com/osense/dotfiles/blob/master/.XCompose (alternate link: http://lpaste.net/169816).

Some of the shortcuts deviate from LaTeX shortcuts. The reasoning behind them may be unclear; I will try to explain some of them. \impl, short for implication, inserts . \impr inserts implication in the opposite direction, l in \impl now standing for left and r in \impr standing for right. Finally, \impb inserts an implication in both directions: . There are also times when LaTeX shortcuts are too wordy, e.g. \circledast for . I have elected to use Agda-like shortcuts in these situations, \O* in this case.

This configuration file is also missing many more advanced Unicode characters.