如何更改宏以将 \begin{theorem} ... \end{theorem} 替换为 \theorem？

Question

为了陈述一个定理，我们通常会这样做：

\begin{theorem}

... (statement) ...

\end{theorem}

我想更改宏以便能够使用\theorem如下方法\section：

\theorem

... (statement) ...

有可能做到吗？我们可以使用定义/引理/命题来代替定理（我使用 amsclass documentclass）。

Answer 1

用不同的名字定义你的定理：

\newtheorem{theoremx}{Theorem}

然后做

\newcommand{\theorem}[1]{\begin{theoremx}#1\end{theoremx}}

现在比较

\begin{theoremx}
This is the statement.
\end{theoremx}

和

\theorem{This is the statement.}

并决定这是否值得付出努力。

如果你决定采用这种策略（我绝对不推荐），你可以这样做

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\newargumenttheorem}{momo}
 {
  \NewDocumentCommand{#1}{om}
   {
    \IfValueTF{##1}
     {
      \begin{\cs_to_str:N #1-inner}[##1] ##2 \end{\cs_to_str:N #1-inner}
     }
     {
      \begin{\cs_to_str:N #1-inner} ##2 \end{\cs_to_str:N #1-inner}
     }
   }
  \IfValueTF{#2}
   {
    \newtheorem{\cs_to_str:N #1-inner}[#2-inner]{#3}
   }
   {
    \IfValueTF{#4}
     {
      \newtheorem{\cs_to_str:N #1-inner}{#3}[#4]
     }
     {
      \newtheorem{\cs_to_str:N #1-inner}{#3}
     }
   }
 }
\ExplSyntaxOff

\newargumenttheorem{\theorem}{Theorem}[section]
\newargumenttheorem{\lemma}[theorem]{Lemma}
\newargumenttheorem{\definition}{Definition}

\begin{document}

\section{Test}

\definition{This is a definition.}

\lemma{This is a lemma.}

\theorem[Important]{\label{important}This is a theorem.}

Theorem \ref{important} is very important.

\end{document}

Answer 2

该theorem环境与许多其他 LaTeX 环境一样，已经具有宏\theorem。

\documentclass{article}
\newtheorem{theorem}{Theorem}

\begin{document}
\section{Introduction}
Theorems can easily be defined

\theorem {
Let $f$ be a function whose derivative exists in every point, then $f$ 
is a continuous function.
}

\end{document}

编辑：

避免@PhelypeOleinik 指出的问题的另一种选择：

\documentclass{article}
\newtheorem{theorem}{Theorem}

\let\oldtheorem\theorem
\let\endoldtheorem\endtheorem
\renewcommand\theorem[1]{\begin{oldtheorem}#1\end{oldtheorem}}

\begin{document}
\section{Introduction}
Theorems can easily be defined

\theorem {
Let $f$ be a function whose derivative exists in every point, then $f$ 
is a continuous function.
} 

Let $f$ be a function whose derivative exists in every point, then $f$ 
is a continuous function

\end{document}

Answer 3

要回答您在评论中提到的版本，您可以简单地这样做：

\newcommand{\mytheorem}[1]{\begin{theorem}#1\end{theorem}}

这样就行了。不过还没有测试过。