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In my paper I need a letter $\mathbb{R}$ with a small circle above it. Currently I'm using the following command:
\newcommand{\obbR}{{\mbox{\kern1.4pt \raisebox{7pt} {\scriptsize$\circ$} \kern-9.1pt}\mathbb{R}}}
But unfortunately it works only with standard font size. The question is how to make a command for this "composed letter", which works with all font sizes.

Actually, I have two problems with writing of this "universal" command.
1. I don't know, how can one make values font-dependent.
2. I don't know, how can one make the small circle, I should put above R, smaller, than \scriptsize\circ.

share|improve this question
One thing that you asked about which wasn't answered is your question 1. I think the problem is that you're specifying lengths and sizes it terms of pt. Maybe if you use em units your commands will scale with the current font context. Can somebody answer this part of his question directly? I think it's interesting. – Geoff Aug 30 '10 at 12:17
up vote 9 down vote accepted

I think you are looking for the \mathring accent. $\mathring{\mathbb{R}}$ should do what you want.

share|improve this answer
Also have a look at tex.stackexchange.com/questions/14/how-to-look-up-a-math-symbol for how to easily find a particular symbol. – Caramdir Aug 28 '10 at 11:07
Thank you, Willie Wong, it works. I will use it. The only problem I see is that this ring, produced with \mathring seems to be a bit too small. But, I believe, it's ok. Thank you, Caramdir, there are useful links there. – fiktor Aug 28 '10 at 11:45

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