%%
%% The LaTeX Companion, 3ed
%%
%% Example 2-4-21 on page I-95 in "showkeys, refcheck --- Displaying \& checking reference keys".
%%
%% 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{231.0pt}
% small headings for the example
\makeatletter
\renewcommand\section{\@startsection{section}{1}{\z@}%
{-1.25ex \@plus-1ex \@minus-.2ex}%
{.5ex}%
{\normalfont\large\bfseries}}
\renewcommand\subsection{\@startsection {subsection}{2}{\z@}%
{-1.ex \@plus -.5ex \@minus -.2ex}%
{.3ex}%
{\normalfont\bfseries}}
\makeatother
% to account for the use of the margin
\addtolength\textwidth{-80pt}
%StartShownPreambleCommands
\usepackage{amsmath,refcheck}
%StopShownPreambleCommands
\begin{document}
\section{An example}\label{sec}
\subsection{A subsection}\label{unused}
Section~\ref{sec} shows the use of the
\texttt{refcheck} package with a
reference to equation~(\ref{eq}).
\begin{align} a &= b \label{eq} \\
a &< b \label{eq2} \\
a &> b \end{align}
\end{document}
