%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-2-11 on page 475.
%%
%% 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{207.0pt}

\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{gather}
  D(a,r) \equiv \{ z \in \mathbf{C}
         \colon |z - a| < r \}    \notag \\
  \operatorname{seg} (a, r) \equiv
    \{ z \in \mathbf{C} \colon
      \Im z < \Im a, \ |z - a| < r \}    \\
    C (E, \theta, r) \equiv
    \bigcup_{e \in E} c (e, \theta, r)
\end{gather}
\end{document}
