Unicode char \u8:χ not set up for use with LaTeX: Solution (made easy with Emacs)

For years I regularly stumbled over LaTeX-Errors in the form of Unicode char \u8:χ not set up for use with LaTeX. I always took the chickens path and replaced the unicode characters with the tex-escapes in the file. That was easy, but it made my files needlessly unreadable. Today I decided to FIX the problem once and for all. And it worked. Easily.

Firstoff: The problem I’m facing is that my keyboard layout [1] makes it effortless for me to input characters like ℂ Σ and χ. But LaTeX cannot cope with them out-of-the-box. Org-mode [2] already catches most of these problems, so I can write things like x² instead of x^2, but occasionally it stumbles.

The solution to that is actually pretty simple: I only need to declare the escapes-sequences LaTeX should use when it sees one of the characters (to be used before \begin{document}!):

\DeclareUnicodeCharacter{03C7}{\chi}

Or in org-mode:

#+LaTeX_HEADER: \DeclareUnicodeCharacter{03C7}{\chi}

To do this more easily, you can use the uniinput.ins [3] and uniinput.dtx [4] from the neo-layout project [1]. Run latex uniinput.ins to generate uniinput.sty which you can put next to your latex files and use with \usepackage{uniinput} (instructions in German [5]).

Thanks go to Wikibooks:LaTeX [6] for this. Their solution suggests then to read several Unicode definition documents for tracking down the codepoint of the character. But we can make that easier with Emacs [7] (almost everything is easier with Emacs ☺).

Instead of browsing huge documents manually, we simply rely on the unicode-definitions in Emacs: Move the cursor over the char and execute M-x describe-char.

When used with χ, this shows the following output:

             position: 672 of 35513 (2%), column: 0
            character: χ (displayed as χ) (codepoint 967, #o1707, #x3c7)
    preferred charset: unicode-bmp (Unicode Basic Multilingual Plane (U+0000..U+FFFF))
code point in charset: 0x03C7
… (and a bit more) …

What we need is code point in charset: Just leave out the 0x and you have the codepoint.

For the document I currently write, I now use the following definitions:

#+LaTeX_HEADER: \DeclareUnicodeCharacter{03C7}{\chi}
#+LaTeX_HEADER: \DeclareUnicodeCharacter{B2}{^{2}}

And that makes χ² work.

Happy Hacking - and have fun with Emacs Org-Mode!