%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-3-9 on page I-339 in "lineno --- Numbering lines of text".
%%
%% 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}
\setlength\marginparsep{20pt}
\addtolength\textwidth{-30pt}
\usepackage{microtype} % improve h&j
\tolerance=4000
%StartShownPreambleCommands
\usepackage{lipsum,lineno} \linenumbers
\newenvironment{numarrows}
{\par\renewcommand\makeLineNumber
{\llap{\LineNumber$\to$ }}}{\par}
\newenvironment{arrows}
{\par\renewcommand\makeLineNumber
{\rlap{\hspace{\textwidth} $\gets$}}}{\par}
%StopShownPreambleCommands
\begin{document}
\begin{numarrows} \lipsum[1][1] \end{numarrows}
\begin{arrows} \lipsum[2][1] \end{arrows}
\textbf{This paragraph has normal numbering.}
\begin{numarrows} \lipsum[3][1] \end{numarrows}
\end{document}
