\documentclass{report}

\input{../preamble}

\newcommand{\lean}[2]{\leanref{../#1.html\##2}{#2}}
\newcommand{\leanPretty}[3]{\leanref{../#1.html\##2}{#3}}

\begin{document}

\header
  {A Mathematical Introduction to Logic}
  {Herbert B. Enderton}

\tableofcontents

% Sets first chapter to `0` to match Enderton book.
\setcounter{chapter}{0}
\addtocounter{chapter}{-1}

\chapter{Useful Facts About Sets}%
\label{chap:useful-facts-about-sets}

\section{\unverified{Lemma 0A}}%
\label{sec:lemma-0a}

Assume that $\langle x_1, \ldots, x_m \rangle =
  \langle y_1, \ldots, y_m, \ldots, y_{m+k} \rangle$.
Then $x_1 = \langle y_1, \ldots, y_{k+1} \rangle$.

\begin{proof}

  \lean{Bookshelf/Enderton/Chapter\_0}{Enderton.Chapter\_0.lemma\_0a}

\end{proof}

\end{document}