%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-1-43 on page I-288 in "thmtools --- Advanced theorem declarations".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{141.0pt}

  \usepackage{microtype}

  \addtolength\textwidth{-12pt}     % for the example in the book

%StartShownPreambleCommands
\usepackage{amsthm,thmtools}
\declaretheoremstyle[spaceabove=9pt, spacebelow=9pt,
    headindent=-12pt, headfont=\sffamily\bfseries,
    headpunct=:, bodyfont=\itshape, break]{breakstyle}
\declaretheorem[style=breakstyle,title=Exercise]{exa}
%StopShownPreambleCommands

\begin{document}
\begin{exa}[Most Active Author]
  Find the author responsible for the largest number of
  packages described in The \LaTeX\ Companion 3rd edition.
\end{exa}
\end{document}