\documentclass{book}
\usepackage{amsmath}
\begin{document}
\begin{displaymath}
\binom{n}{k}\qquad\mathrm{C}_n^k
\end{displaymath}
\begin{displaymath}
\int f_N(x) \stackrel{!}{=} 1
\end{displaymath}
\begin{displaymath}
\sum_{i=1}^{n} \qquad
\int_{0}^{\frac{\pi}{2}} \qquad
\prod_\epsilon
\end{displaymath}
\end{document}
http://s13/middle/6c9ce165tbcff41ad632c&690

-----------------------------------------------------------

\documentclass{book}
\usepackage{amsmath}
\begin{document}
\begin{displaymath}
\sum_{\substack{0<i<n \\ 1<j<m}}
P(i,j) =
\sum_{\begin{subarray}{l}
i\in I\\
1<j<m
\end{subarray}} Q(i,j)
\end{displaymath}
\end{document}

http://s7/middle/6c9ce165tbcff56cf3c46&690