%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-2-23 on page 481.
%%
%% Copyright (C) 2004 Frank Mittelbach, Michel Goossens,
%%    Johannes Braams, David Carlisle, and Chris Rowley
%%
%% 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{ttctexamargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{183.0pt}

\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
Empty line before display:

\[  a \neq b   \]

In both cases, too much space before! \ldots

\begin{equation} a \neq b \end{equation}

\ldots\ and not a lot of space after!
\end{document}