\begin{definition}[Definition:Contour Integral/Complex/Closed]
Let $C$ be a closed contour in $\C$.
Then the symbol $\ds \oint$ is used for the '''contour integral''' on $C$.
The definition remains the same:
:$\ds \oint_C \map f z \rd z := \sum_{i \mathop = 1}^n \int_{a_i}^{b_i} \map f {\map {\gamma_i} t} \map {\gamma_i'} t \rd t$
\end{definition}