%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-8-4 on page II-575 in "bibunits --- Bibliographies for arbitrary units".
%%
%% 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{124.20126pt}

\setlength\textheight{12\baselineskip}
% Small headings for the example
\makeatletter
\renewcommand\section{\@startsection{section}{1}{\z@}%
                                    {-1.25ex \@plus-1ex \@minus-.2ex}%
                                    {.8ex}%
                                    {\large\bfseries}}
\makeatother
% Do not process top-level aux file with BibTeX

%StartShownPreambleCommands
\usepackage{bibunits}
\defaultbibliographystyle{alpha}
\defaultbibliography{tlc-ex}
%StopShownPreambleCommands

\begin{document}
\section{First one}
\begin{bibunit}[plain]
 \cite{GNUMake} was used to
 produce \cite{Knuth:TB10-1-31}.
 \putbib[tlc]
\end{bibunit}
\section{Another one}
\begin{bibunit}% default used
 As described by \cite{book1}
 \ldots
 \putbib       % default used
\end{bibunit}
\end{document}