\documentclass{article}
\usepackage{graphics}
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\begin{document}

\begin{equation}
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\put(11,11){\makebox(0,0){\includegraphics{a.eps}}}
\put(11,11){\makebox(0,0){$\times$}}
\end{picture}}
+
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+
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+
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\put(11,11){\makebox(0,0){\includegraphics{a.eps}}}
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\end{equation}

\end{document}