Hi I ve got this error message
Runaway argument?
\x@protect \[\protect \[ \@nil \@ifpackageloaded {amstex}{\def \@tempa \ETC.
Paragraph ended before \@tempa was complete.
<to be read again> \par
l.435 \newenvironment{proof}[1][\proofname]{\par
while compiling this in XeLaTex
\documentclass[12pt]{book}%thesis
\usepackage{polyglossia}
\setmainlanguage{english}
\usepackage[numbers]{natbib}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{makeidx}
\usepackage{graphicx}
\usepackage{epigraph}
\usepackage{pdfpages}
\usepackage{url}
\usepackage{breqn}
\usepackage{setspace}
\usepackage{dsfont}
\usepackage{eurosym}
\usepackage{epstopdf}
\usepackage{color}
\usepackage{setspace}
\usepackage{titling}
\begin{document}
bla
\end{document}
What seems to be the pbm?