%% 
%%  An UIT Edition example
%% 
%%  Example 06-12-12 on page 112.
%% 
%%  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{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{70}
\renewcommand\theequation{6.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{align}
\prod_{j\ge0}
\raisebox{-.8ex}{$\displaystyle
  \left(\begin{array}{@{}c@{}}\displaystyle\sum_{k\ge0}a_{jk}z^k\end{array}
  \right)$} = \sum_{n\ge0}z^n\,
\raisebox{-1.75ex}{$\displaystyle
  \left(\begin{array}{@{}c@{}}\displaystyle\sum_{\scriptstyle k_0,k_1,\ldots
    \ge0\atop\scriptstyle k_0+k_1+\cdots=n}
    \kern-.8em a_{0k_0}a_{1k_1}\ldots\end{array}\,\right)$}
\end{align}
\end{document}