我正在尝试创建一个定理环境，我可以使用它来重复书中先前陈述的定理，但将其编号与第一个实例相同。我找到了某种解决方案：
\documentclass{article}
\usepackage{amsthm}
\newtheorem{theorem}{Theorem}
\newcounter{thmC}
\newtheorem{rethm}[thmC]{Theorem}
\newenvironment{retheorem}[1]%
{\setcounter{thmC}{#1}%
\addtocounter{thmC}{-1}%
\begin{rethm}}%
{\end{rethm}\ignorespacesafterend}
\begin{document}
\begin{theorem}\label{theorem:Hi}
Hi this is my theorem.
\end{theorem}
\begin{theorem}\label{theorem:another}
Another theorem.
\end{theorem}
\begin{theorem}\label{theorem:third}
third theorem
\end{theorem}
\begin{retheorem}{\ref{theorem:third}}
third theorem
\end{retheorem}
\begin{retheorem}{\ref{theorem:another}}
Another theorem.
\end{retheorem}
\begin{retheorem}{\ref{theorem:Hi}}
Hi this is my theorem.
\end{retheorem}
\end{document}
它几乎可以工作，但是存在间距问题。
我进一步担心的是，这种方法是否适用于标有以下部分的定理
\numberwithin{theoremC}{section}
\newtheorem{theorem}[theoremC]{Theorem}
答案1
restatable此功能已由环境提供thmtools包；该包还提供了一个continues密钥，它在两种情况下处理定理计数器从属于另一个定理计数器的情况：
\documentclass{article}
\usepackage{amsthm}
\usepackage{thmtools,thm-restate}
\declaretheorem[numberwithin=section]{theorem}
\begin{document}
\section{Test section one}
\begin{theorem}[label=thm:key]
This is a theorem that will be continued later.
\end{theorem}
\begin{restatable}{theorem}{Hi}
This is my first restatable theorem.
\end{restatable}
\begin{restatable}{theorem}{another}
This is my second restatable theorem.
\end{restatable}
\section{Test section two}
\begin{restatable}{theorem}{third}
This is my third restatable theorem.
\end{restatable}
\section{Test section three}
\third*
\another*
\Hi*
\begin{theorem}[continues=thm:key]
And here I expand my theorem.
\end{theorem}
\end{document}
然而，可重述定理和标准定理在垂直间距上仍然存在一些差异。