proper type-setting of cartouches (requires T1);
\usepackage[T1]{fontenc} is default for mkroot;
\usepackage[utf8]{inputenc} is obsolete in lualatex;
\documentclass[10pt,a4paper,twoside]{article}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{latexsym,theorem}
\usepackage{isabelle,isabellesym}
\usepackage{pdfsetup}\urlstyle{rm}
\begin{document}
\pagestyle{headings}
\pagenumbering{arabic}
\title{Verification of The SET Protocol}
\author{Giampaolo Bella, Fabio Massacci, Lawrence C. Paulson et al.}
\maketitle
\tableofcontents
\begin{center}
\includegraphics[scale=0.5]{session_graph}
\end{center}
\newpage
\parindent 0pt\parskip 0.5ex
\input{session}
\end{document}