# omicron not working in LaTeX

I find out that \omicron is not working in LaTeX, at least for the latest MacTeX I installed.

MWE:

\documentclass{article}
\begin{document}
$$\omicron$$
\end{document}


From List of Mathematical Symbols in Wikibooks there is such command. But from AMS Short Math Guide it says

In the list of lowercase letters there is no omicron because it would be identical in appearance to Latin o.

My question would NOT be why there isn't such command, how I can get it work, etc.

But rather, why things like this documented in many places (the wikibook is not the only place listing that command), but almost no one seems to mention it doesn't work (the AMS guide is the few example saying it).

• You could use \newcommand\omicron{o} but I don't understand the question, by default there is no \omicron command, how can documentation document commands that don't exist. It looks to be simply an error in the wiki you reference – David Carlisle Mar 15 '15 at 18:09
• As it often happens, people drag information from one place to another without checking the facts or using a simple cite statement to blame the guilty. Pity. – Johannes_B Mar 15 '15 at 18:16
• The information on that Wikibooks page is rather disputable in several parts. See for example the treatment of binomial coefficients, which is ridiculous. The advice regarding \dd is similarly hilarious. Happily somebody has already removed the reference to \omicron. – egreg Mar 15 '15 at 19:03
• Thanks everyone. I was thinking that command was there and got deleted in a newer version of LaTeX. But I was surprised the wrong information is propagating for so long. As I said many of the search results of tables of LaTeX symbols would actually has that. I asked such question because when I test those tables, the code resulted in errors. In this case I think may be because no one is really using the \omicron code so even if they put it there, no one will notice it is wrong. And people just copy and paste things "irresponsibly". – Kolen Cheung Mar 23 '15 at 22:45

\omicron is not mentioned in most latex guides as there is no such command by default. The mention of it in the wikibook was an error that has apparently been corrected since you asked the question.

You could use

 \newcommand\omicron{o}


if you are using classic TeX fonts that do not have a full Greek math alphabet.

If you are using xelatex or lualatex you could use unicode based math fonts that do have full math alphabets and an omicron that is distinct from o.

The unicode-math offers \upomicron for upright omicron, and \mitomicron for math italic omicron, and defines \omicron as an alias for \mitomicron.

• \omicron is defined by the unicode-math package (tested with 2015/09/24 v0.8c version). – asr Jun 4 '16 at 16:14
• @asr sorry my mistake (I looked before begin{document} , even though in principle I know the package delays the setup:-) I'll edit, thanks – David Carlisle Jun 4 '16 at 20:22