diff --git a/thys/Group-Ring-Module/document/root.tex b/thys/Group-Ring-Module/document/root.tex
--- a/thys/Group-Ring-Module/document/root.tex
+++ b/thys/Group-Ring-Module/document/root.tex
@@ -1,34 +1,35 @@
 \documentclass[11pt,a4paper]{report}
 \usepackage{isabelle,isabellesym}
 \usepackage{amssymb}
 \usepackage[english]{babel}
 \usepackage[utf8]{inputenc}
+\usepackage{textcomp}
 
 % this should be the last package used
 \usepackage{pdfsetup}
 
 % urls in roman style, theory text in math-similar italics
 \urlstyle{rm}
 \isabellestyle{it}
 
 
 \begin{document}
 
 \title{Group Ring Module}
 \author{Hidetsune Kobayashi, L. Chen, H. Murao}
 \maketitle
 
 \begin{abstract}
 The theory of groups, rings and modules is developed to a great depth. Group
 theory results include Zassenhaus's theorem and the Jordan-Hoelder
 theorem. The ring theory development includes ideals, quotient rings and the
 Chinese remainder theorem. The module development includes the Nakayama lemma,
 exact sequences and Tensor products.
 \end{abstract}
 
 \tableofcontents
 
 % include generated text of all theories
 \input{session}
 
 \end{document}