（这是这个。
考虑下面的代码：
\documentclass{article}
\usepackage{amsmath}
\newtheorem{fruit}{Definition of a kind of fruit}
\begin{document}
Let's define some fruits. But first some text to reach till the right margin and even a little further.
\begin{fruit}[Banana, as found in the book \\ {\cite[chapter 31]{ref1}}]
A banana is a yellow fruit that grows on a tree.
\end{fruit}
\begin{thebibliography}{9}
\bibitem{ref1} O. Outan. The big book of bananas. Fruit Editions Ltd.
\end{thebibliography}
\end{document}
这使：
标题里为什么没有换行符？