如何将定理的数字放在括号里？

Question

我想要的是这样的：

（1.1）定理。等等……

我使用 ntheorem 包交换了定理的编号和名称。那么，如何将编号括起来？

\documentclass{book}
 \usepackage{amsmath}
 \usepackage[amsmath,thmmarks]{ntheorem}
  \theoremstyle{change}
  \theorembodyfont{\itshape}
   \newtheorem{thm}{Theorem}[section]

\begin{document}
 \chapter{A Chapter}
 \section{A section}
   \begin{thm}
     A theorem.
   \end{thm}
\end{document}

Answer 1

定义新的定理样式mychange

\makeatletter 
 \newtheoremstyle{mychange}%
  {\item[\hskip\labelsep \theorem@headerfont (##2)\ ##1\theorem@separator]}%
  {\item[\hskip\labelsep \theorem@headerfont (##2)\ ##1\ (##3)\theorem@separator]}
\makeatother

并使用

\theoremstyle{mychange}

平均能量损失

\documentclass{book}
 \usepackage{amsmath}
 \usepackage[amsmath,thmmarks]{ntheorem}

\makeatletter 
 \newtheoremstyle{mychange}%
  {\item[\hskip\labelsep \theorem@headerfont (##2)\ ##1\theorem@separator]}%
  {\item[\hskip\labelsep \theorem@headerfont (##2)\ ##1\ (##3)\theorem@separator]}
\makeatother

  \theoremstyle{mychange}
  \theorembodyfont{\itshape}
   \newtheorem{thm}{Theorem}[section]

\begin{document}
 \chapter{A Chapter}
 \section{A section}
   \begin{thm}
     A theorem.
   \end{thm}
\end{document}