%% 
%%  An UIT Edition example
%% 
%%  Example 10-06-1 on page 208.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{201.70511pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\usepackage{amsmath}
\let\dst\displaystyle
\StopShownPreambleCommands
\begin{document}
\begin{align*}
\prod_{k\ge0}\dfrac{1}{(1-q^kz)} &=
  \dfrac{\dst\sum_{n\ge0}z^n}
        {\dst\prod_{1\le k\le n}(1-q^k)}
\end{align*}
\end{document}