考虑遵循 MWE：
\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}
得出
如你所见，定义名称
[{Banana, as found in the book \cite[chapter 31]{ref1}}]
包含引文，因此{}为了避免错误，将整个名称放在中间。结果发现出现了悬垂。有没有一种直接的方法可以在这里获得换行符？
更新
我希望该定理的第一行是合理的文本。
在这种情况下，是否可以在引用内部进行拆分？
...................................[1，
第 31 章。香蕉是
答案1
amsmath不涉及定理定义，但 AMS 包amsthm确实提供了允许在此处换行的扩展定理声明。
\documentclass{article}
\usepackage{amsmath}
\usepackage{amsthm}
\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}