%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-3-13 on page II-493 in "The basic syntax".
%%
%% 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{87.0pt}

%% Do not show the bibliography itself in the example,
%% so put it on a separate page:
\AtEndDocument{\newpage \bibliography{tlc}}
\setlength\parindent{0pt}

%StartShownPreambleCommands
\usepackage{natbib}
\bibliographystyle{agsm}
\newcommand\possessivecite[1]{\citeauthor{#1}'s \citeyearpar{#1}}
%StopShownPreambleCommands

\begin{document}
\citeauthor{Knuth-CT-a}'s \citeyearpar{Knuth-CT-a} \\
\possessivecite{Knuth-CT-a}
\end{document}
