# Interior of a set notation

I'm trying to match this:

$A^0$
$A^o$
$A^\circ$


None of these match the above image however.

• Welcome to TeX.SX! It could be $A^{\mathrm{o}}$. Can you add a source for such a notation? Feb 24, 2016 at 0:01
• Unfortunately with that the circle is too low, but definitely matches it better than the others (but not perfectly). As for a source, the image was taken from a scan. (I would like to confirm that I am user99133 but had somehow managed to post under a guest account) Feb 24, 2016 at 0:05
• font differences are to be expected, but what is the intended meaning, is that an index 0 or a superscipt O when taken in context? Feb 24, 2016 at 0:07
• It's the interior of the set A, usually seen in topology. The index is much closer to an o rather than a 0. As for font differences, I understand that but would like to match it as close as possible. Feb 24, 2016 at 0:10
• wikipedia suggests that it is ^o with a lowercase o en.wikipedia.org/wiki/Interior_%28topology%29 Feb 24, 2016 at 0:10

The symbol seems to be an upright “o”; in order to raise it more than it would be with $A^{\mathrm{o}}$, you can define a macro.

\documentclass{article}

\newcommand{\interior}[1]{%
{\kern0pt#1}^{\mathrm{o}}%
}

\begin{document}

$\interior{A} \interior{B}$

\end{document}


• This is perfect, thank you very much! I would choose this as the answer if I could but I have no idea how to get back into the guest account. So instead, take an upvote. Feb 24, 2016 at 0:25
• @IrregularUser See stackoverflow.com/help/merging-accounts Feb 24, 2016 at 10:11
• @egreg. Why has the 0pt kern the effect of raising the exponent? I can't understand.
– User
Mar 2, 2016 at 17:56
• @User In this case TeX ignores the metric information of A and just looks at the height of the box, because the nucleus of the math atom is not a single math character. Mar 2, 2016 at 18:37

The latex kernel contains the \mathring accent for that:

Edit :

You might prefer to use the \ring command from mathabx. Here is a code to use it without replacing all maths fonts: it defines the \abxring mathaccent.

\DeclareFontFamily{U}{mathb}{\hyphenchar\font45}
\DeclareFontShape{U}{mathb}{m}{n}{ <-6> matha5 <6-7> matha6 <7-8>
mathb7 <8-9> mathb8 <9-10> mathb9 <10-12> mathb10 <12-> mathb12 }{}
\DeclareSymbolFont{mathb}{U}{mathb}{m}{n}

\DeclareMathAccent{\abxring}{0}{mathb}{"38}

\DeclareFontFamily{U}{mathb}{\hyphenchar\font45}
\DeclareFontShape{U}{mathb}{m}{n}{ <-6> matha5 <6-7> matha6 <7-8>
mathb7 <8-9> mathb8 <9-10> mathb9 <10-12> mathb10 <12-> mathb12 }{}
\DeclareSymbolFont{mathb}{U}{mathb}{m}{n}


I'd use the first, but take your pick:-)

\documentclass{article}

\begin{document}

$A^\mathrm{o} \quad A\strut^\mathrm{o} \quad A\mkern-1mu\vrule width0pt height 1em^\mathrm{o} \quad A\mkern-1mu{\vrule width0pt height 2ex}^\mathrm{o}$

\end{document}


Above all, use a macro, that way you can change it later (or even provide it with a few intelligence), here's a basic version

\newcommand*\interior[1]{#1^{\mathsf{o}}}


You can let \interior be intelligent, and do (#1)^{\mathsf{o}} in case there are a few symbols inside, or even some parenthesis above the whole expression like some notations do.

A bit late to the game, but I’m surprised no one suggested \circ:

\documentclass{article}

\pagestyle{empty}

\newcommand\interior[1]{{#1}^{\circ}}

\begin{document}
$\interior{A}$
\end{document}


If you want bold symbols for sets, you might try \mathbfit from isomath or \symbfit from unicode-math.