# How to write non-english characters in the math mode?

I'd like to have the Danish letter ø in my text. It's very simple when I mean plain text: {\o}. How can I achieve the same result in the math mode? If I add {\o} to my formulas, this character isn't printed.

I believe that my question isn't a dupplicate of any of these: 1 or 2, because I don't want to be able to write ø in the math mode. On the contrary, I'd like to use the command {\o} as I do in the text mode (it is more convenient for me since I'm not used to the Danish keyboard).

• Exactly what do you need ø for in math? If it is as an index, use R_{\textup{sø}} or similar. ø (and \o)is generally not allowed in math mode. – daleif Jul 11 '16 at 11:30
• @daleif, as an index. Thank you, it works:) – user2738748 Jul 11 '16 at 12:17
• I've added it as an answer – daleif Jul 11 '16 at 12:26

Generally non-ascii letters are not allowed in math mode, there are various methods to allow them, but generally non-english letters are only used in two cases within math

1. As a part of an index. Here it is recommended to use _{\textup{sø}} or _{\textnormal{sø}} as this switches back to the (upright) text font where non-english letters are allowed

2. The other is textual comments in a displayed formula. Here \text{....} is recommended.

$f(x)>0 \qquad \text{for all x>0}$


as this also switch to the context correct font.

Note that it is not recommended to use \text for 1. as textual indices should be upright and \text{text} will be italic in an italic context.

Note this shortcut (due to @egreg)

\newcommand\tsub[1]{_{\textup{#1}}}


Then use $R\tsub{sø}$ a bit faster to write, and also easier to change if you later on want to change \textup into \textnormal