Math & Science ⇒ citation in maths mode

[latex_fun]

Hi Stefan,
If I try to put a citation in maths mode I get an error:
! LaTeX Error: Command \upshape invalid in math mode

How can I do this correctly?
Kind regards

MWE:

Code: Select all

 
 \documentclass{amsart}
\usepackage{amsfonts}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}
\usepackage{soul}
\usepackage[autostyle]{csquotes}

\title{Let's help Sister Mary}
\author{John Bellushi}
% These will be typeset in italics
\newtheorem{Theorem}{Theorem}[section]
\newtheorem{Corollary}[Theorem]{Corollary}
\newtheorem{Hypothesis}[Theorem]{Hypothesis}
\newtheorem{Proposition}[Theorem]{Proposition}
\newtheorem{Lemma}[Theorem]{Lemma}
% These will be typeset in Roman
\theoremstyle{definition}
\newtheorem{Definition}[Theorem]{Definition}
\newtheorem{Example}[Theorem]{Example}
\newtheorem{Fact}[Theorem]{Fact}
\newtheorem{Remark}[Theorem]{Remark}
\begin{document}
%\pagenumbering{gobble}
\begin{abstract}
 Save the orphans!
\end{abstract}

\maketitle 

%\newpage
\pagenumbering{arabic}
\section{Introduction}
yep
\section{The number}
It adds up:
\begin{equation*}
      55+2\ \cite{dopey}
\end{equation*}



\begin{thebibliography}{1}

\bibitem{dopey}
  Dope, The, ``I'm so sleepy''
\end{thebibliography}
\end{document}