[Tex/LaTex] Interior of a set notation

Question

I'm trying to match this:

I've already tried (in amsmath)

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

None of these match the above image however.

Answer 1

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}