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\begin{document}

\begin{table}[]
\begin{center}

\begin{tabular}{c||c|c}
 $ . $ & $ G $ & $ G_{u} $\\ \hline \hline 
$ G$ & $G\circ C$ &$ G \circ G_{u}$\\  \hline
$ G_{u}$ &$ G_{u} \circ G$ &$G_{u}oG_{u}$ 

\end{tabular}
\end{center}
\end{table}




\end{document}