\begin{equation}
D(T_d(I_e,Exp_1, Exp_2))=
\left\{ \begin{array}{ll}
             1, & \text{if $Exp_1$ is superior} \\
             2, & \text{if $Exp_2$ is superior} \\
           \end{array} \right.
\label{eq:4}
\end{equation}
