src/HOL/Number_Theory/document/root.tex

proper syntax;

\documentclass[11pt,a4paper]{article}
\usepackage{graphicx}
\usepackage{isabelle,isabellesym}
\usepackage{pdfsetup}

\urlstyle{rm}
\isabellestyle{it}


\begin{document}

\title{Various results of number theory}
\maketitle

\tableofcontents

\begin{center}
  \includegraphics[width=\textwidth,height=\textheight,keepaspectratio]{session_graph}
\end{center}

\newpage

\parindent 0pt\parskip 0.5ex

\input{session}

\end{document}