新环境中的空间

Question

我观察到我自制的环境存在不良行为。以下代码有时会在环境头后创建空格，有时则不会。

\documentclass[a4paper]{article}

\usepackage[utf8]{inputenc}
\usepackage{ifthen}

\newenvironment{Theorem}[1][]{%
    \medskip%
    \par%
    \noindent%
    \textbf{Theorem.}%
    \ifthenelse{ \equal{#1}{} }{}{ (#1)}%
    \it%
    }%
    {%
    \smallskip\par%
    }

\newenvironment{Theorem2}{%
    \medskip%
    \par%
    \noindent%
    \textbf{Theorem.}%
    \it%
    }%
    {%
    \smallskip\par%
    }

\begin{document}

\begin{Theorem}
That is a cool Theorem
\end{Theorem}

\begin{Theorem}[of some famous guy]
    That is a cool Theorem
\end{Theorem}

\begin{Theorem2}
another cool theorem
\end{Theorem2}

\begin{Theorem2}%
another cool theorem
\end{Theorem2}

\end{document}

结果是：

有没有办法强制 LaTeX 忽略环境定义中的所有正常空格，这样我只能通过添加空格\space？

我可以在环境定义中添加一些内容，使其忽略环境调用后直接出现的所有空格和 par，以便

\begin{Theorem2}
some text
\end{Theorem2}

产生的结果与

\begin{Theorem2}%
some text
\end{Theorem2}

？

Answer 1

\ignorespaces是的！在第一个参数的末尾使用\newenvironment

\documentclass{article}
\newenvironment{Theorem2}{%
    \medskip%
    \par%
    \noindent%
    \textbf{Theorem.}%
    \itshape\ignorespaces%
    }%
    {%
    \smallskip\par%
    }
\begin{document}
  \begin{Theorem2}
  some text
  \end{Theorem2}
\end{document}

\ignorespaces是一个忽略下一个空格直到需要输出文本的原语。例如，当您执行此操作时，将生成\newenvironment{thm}{}{}一个宏\thm，而该宏又是该\begin{thm}命令执行的最后一个宏。

Answer 2

是的，有：使用xparse和利用在空间范围内\ExplSyntaxOn被忽略的空间；可以用来~插入一个真正的空间。

\documentclass[a4paper]{article}

\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentEnvironment{Theorem}{o}
 {
  \par\addvspace{\medskipamount}
  \noindent
  \normalfont
  \textbf{Theorem.~}
  \IfValueT{#1}{(#1)~}
  \itshape\ignorespaces
 }
 {
  \par\addvspace{\smallskipamount}
 }
\ExplSyntaxOff

\begin{document}

Some text before the theorem to see the vertical spacing
in context.

\begin{Theorem}
That is a cool Theorem
\end{Theorem}

Some text after and before the theorem to see the vertical spacing
in context.

\begin{Theorem}[of some famous guy]
    That is a cool Theorem
\end{Theorem}

Some text after the theorem to see the vertical spacing
in context.

\end{document}

我做了一些调整：\medskip和\smallskip在这种情况下是错误的。但是，\smallskipamount如图所示，肯定太小了。\addvspace垂直空间不会累积；使用您的代码，两个连续的定理将被一个小跳跃加上一个中等跳跃分开。

另一方面，\newtheorem*fromamsthm要简单得多。

\documentclass[a4paper]{article}

\usepackage{amsthm}

\newtheorem*{Theorem}{Theorem}

\begin{document}

Some text before the theorem to see the vertical spacing
in context.

\begin{Theorem}
That is a cool Theorem
\end{Theorem}

Some text after and before the theorem to see the vertical spacing
in context.

\begin{Theorem}[of some famous guy]
    That is a cool Theorem
\end{Theorem}

Some text after the theorem to see the vertical spacing
in context.

\end{document}