%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 3-3-21 on page 142.
%%
%% 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{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{111.0pt}

\addtolength\textwidth{-2pt}     % for the example in the book

\StartShownPreambleCommands
\usepackage{ragged2e,amsthm}
\newtheoremstyle{break}%
  {9pt}{9pt}%              Space above and below
  {\itshape\RaggedRight}%  Body style
  {-12pt}%                 Heading indent amount
  {\sffamily\bfseries}{:}% Heading font and punctuation after it
  {\newline}%         Space after heading (\newline = linebreak)
  {}%                 Head spec (empty = same as `plain' style)
\theoremstyle{break}
\newtheorem{exa}{Exercise}
\StopShownPreambleCommands
\begin{document}
\begin{exa}[Active author]
   Find the author responsible for the largest number of
   packages  described in The \LaTeX{} Companion.
\end{exa}
\end{document}