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\begin{equation*}
I_S(a,b)=\left\{
\begin{array}{lr}
0& \text{اگر}\ a\neq 0\ \text{\rl{و}}\ \exists a_0\in(0,a]\ \ \Gamma(a_0,a,b)=\emptyset,\\
a\rightarrow_s b& \text{\rl{در غیر این صورت}}
\end{array}\right.
\end{equation*}

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