superimosing {\circ} on {\sum} in {math-mode}

Question

Possible Duplicate:
\subseteq + \circ as a single symbol (“open subset”)

Is it possible to superimpose a variable size \circ on \sum to compose a symbol just like \oint?

Answer 1

LuaTeX/XeTeX with XITS Math

The symbol ⨊ is Unicode character U+2a0a Modulo two sum. It can be used directly with LuaTeX or XeTeX if the glyph is supported by the used fonts. Example:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{XITS Math}
\begin{document}
\[ ⨊ \] % or \modtwosum
\end{document}

Package fdsymbol

Another font that directly provides the symbol is fdsymbol:

\documentclass{article}
\usepackage{fdsymbol}
\begin{document}
\[ \modtwosum \]
\end{document}

Superimposing

It is also possible to superimpose the symbols, for example:

\documentclass{article}

\makeatletter
\newcommand*{\modtwosum}[1][.4]{%
  \mathop{%
    \mathpalette\@modtwosum{#1}%
  }%
}
\newcommand*{\@modtwosum}[2]{%
  \sbox0{$\m@th#1\sum$}%
  \rlap{%
    \hbox to \wd0{%
      \hspace{0pt plus #2fil}%
      $\m@th#1\circ$%
      \hspace{0pt plus 1fil}%
      \hspace{0pt plus -#2fil}%
    }%
  }%
  {#1\sum}%
}
\makeatother

\begin{document}
\[ \modtwosum \]
\[
  \def\test#1{\modtwosum[#1]_{#1}}
  \test{0}\test{0.2}\test{0.4}\test{0.6}\test{0.8}\test{1}
\]
\end{document}