%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-2-19 on page II-484 in "natbib's approach to number-only references".
%%
%% 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{207.0pt}
% small headings for the example
\makeatletter
\renewcommand\section{\@startsection{section}{1}{\z@}%
                                    {-1.25ex \@plus-1ex \@minus-.2ex}%
                                    {.5ex}%
                                    {\normalfont\normalsize\bfseries}}
\makeatother
%StartShownPreambleCommands
\usepackage{natbib}
\bibliographystyle{plain}
%StopShownPreambleCommands

\begin{document}
\cite{Knuth:TB10-1-31},
\citep{Knuth:TB10-1-31},
\citet{Knuth:TB10-1-31}
\bibliography{tlc}
\end{document}