%% 
%%  An UIT Edition example
%% 
%%  Example 06-12-8 on page 111.
%% 
%%  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{177.70511pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{66}
\renewcommand\theequation{6.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\delimitershortfall=-1pt % fits parenthesis
\begin{align}
\rule[2.5pt]{1cm}{0.2pt} % math axis
\left[ \begin{array}{@{}c@{}}
 \displaystyle\sum_{\substack{%
  1\le i\le p\\1\le j\le q\\1\le k\le r}}
  a_{ij}b_{jk}c_{ki}
\end{array} \right] = A
\rule[2.5pt]{1cm}{0.2pt} % math axis
\end{align}
\end{document}
