\documentclass{ppex}
\nonstopmode
\usepackage {mathptm}
\pagestyle{empty}

\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {mathptm}
The default math mode font is $math\ italic$. This should not be
confused with ordinary \emph{text italic}.
\verb|\mathbf| produces $\mathbf{bold-face\ roman}$ letters.
Greek is available in upper and lower case:
\(\alpha,\beta, \Gamma, \Delta \dots \omega, \Omega\)
There is also a calligraphic font for upper-case letters;
these are produced by the \verb|\mathcal| command:
\( \mathcal{ABCDE} \)


\begin{equation}
 \phi(t)=\frac{1}{\sqrt{2\pi}}
 \int^t_0 e^{-x^2/2} dx
\end{equation}

\begin{equation}
 \prod_{j\geq 0}
 \left(\sum_{k\geq 0}a_{jk} z^k\right)
= \sum_{k\geq 0} z^n
 \left( \sum_{{k_0,k_1,\ldots\geq 0}
         \atop{k_0+k_1+\ldots=n}    }
       a{_0k_0}a_{1k_1}\ldots  \right)
\end{equation}

\begin{equation}
\pi(n) = \sum_{m=2}^{n}
 \left\lfloor \left(\sum_{k=1}^{m-1}
      \lfloor(m/k)/\lceil m/k\rceil
      \rfloor \right)^{-1}
 \right\rfloor
\end{equation}

\begin{equation}
\{\underbrace{%
   \overbrace{\mathstrut a,\ldots,a}^{k\ a's},
   \overbrace{\mathstrut b,\ldots,b}^{l\ b's}}
 _{k+1\ \mathrm{elements}}                   \}
\end{equation}
\end{document}