src/HOL/Algebra/document/root.tex

added lemma

\documentclass[11pt,a4paper]{article}
\usepackage{graphicx}
\usepackage{isabelle,isabellesym}
\usepackage{amssymb}
\usepackage{textcomp}
\usepackage[utf8]{inputenc}
\usepackage[only,bigsqcap]{stmaryrd}
%\usepackage{amsmath}

% this should be the last package used
\usepackage{pdfsetup}

\urlstyle{rm}
\isabellestyle{tt}
\pagestyle{myheadings}

\begin{document}

\title{The Isabelle/HOL Algebra Library}
\author{Clemens Ballarin (Editor)}
\date{With contributions by Jesús Aransay, Clemens Ballarin, Stephan Hohe,
  Florian Kammüller and Lawrence C Paulson \\
  \today}
\maketitle

\tableofcontents

\begin{center}
  \includegraphics[scale=0.5]{session_graph}
\end{center}

\clearpage

\parindent 0pt\parskip 0.5ex
\input{session}

\pagestyle{headings}
\bibliographystyle{abbrv}
\bibliography{root}

\end{document}