%% 
%%  \protect \LaTeX  -Referenz, 1. Auf"|lage 2007
%% 
%%  Example 5-1-1 on page 62.
%% 
%%  Copyright (C) 2007 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.
%% 

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{177.7051pt}
\StartShownPreambleCommands
\usepackage{amsmath}
\newcommand*\dx{\,\mathrm{d}x}
\StopShownPreambleCommands
\begin{document}
\begin{align*}
  \int\limits_1^\infty          \frac{1}{x^2}\dx &= 1\\
  \int\limits_1^\infty\mkern-3mu\frac{1}{x^2}\dx &= 1
\end{align*}
\end{document}