更改描述环境缩进

Question 1

所提出的要求一点也不明确：如果人们只是想将description环境的标签排版为环境的一部分enumerate，那么为什么要使用description？显然，这个问题缺少一些基本信息。一种可能的解释是，这里真正想要的是排版一个常规的description样式标签，并在边距中粘贴一个数字，其对齐方式与的标签类似enumerate。以下示例阐明了我的意思。

\documentclass[a4paper]{amsbook}
\usepackage[T1]{fontenc}
\usepackage{enumitem} % actually redundant, in this example

\newenvironment*{descriptionThatMimicksItemize}{%
  \list{}{\let\makelabel\descriptionTMIlabel}%
}{\endlist}
\newcommand*{\descriptionTMIlabel}[1]{\hss\llap{\upshape #1}}
\makeatletter
  \@ifdefinable\origLabelWidth{\newdimen\origLabelWidth}
  \@ifdefinable\origLabelSep  {\newdimen\origLabelSep}
\makeatother
\newcommand*{\myNumericLabel}[1]{%
  \makebox[\origLabelWidth][r]{#1}\hspace{\origLabelSep}%
}

\begin{document}

\origLabelWidth = \labelwidth
\origLabelSep   = \labelsep
% This is an over-simplification, but for now we can accept it.

The \texttt{enumerate} environment:
\begin{enumerate}
  \item \label{a}
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
  \item \label{b}
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
\end{enumerate}

The first solution:
\begin{descriptionThatMimicksItemize}
  \item[(\ref{a}) Is it this what you want?]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
  \item[(\ref{b}) I wouldn't say so.]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
\end{descriptionThatMimicksItemize}

The second one:
\begin{description}
  \item[\myNumericLabel{(\ref{a})}I'd rather say it's this]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
  \item[\myNumericLabel{(\ref{b})}A label is needed, though]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
\end{description}

\end{document}

输出：产生的输出

如果这是真正的问题，则它涉及将提供的标签分成两个部分，因此超出了设置边距和标签宽度的简单问题。

总之，我认为，在明确具体的要求之前，不可能完全回答这个问题。

添加

我开始怀疑这是否只是我们真正想要的：

\documentclass[a4paper]{amsbook} % or whatever
\usepackage[T1]{fontenc}
\usepackage{hyperref}

\begin{document}

Let \( f\colon A\to B \) be a function.  The following are equivalent:
\begin{enumerate}
  \item\label{a}  $f$ is both injective and surjective;
  \item\label{b}  $f$ is invertible.
\end{enumerate}
Proof:
\begin{enumerate}
  \item[$\ref{a}\Rightarrow\ref{b}$:]
    Pick an element \( b\in B \), and let \( a\in A \) be the unique element 
    that is sent into~$b$ by~$f$\ldots
  \item[$\ref{b}\Rightarrow\ref{a}$:]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
\end{enumerate}

\end{document}

输出：添加代码的输出

当然，超链接按预期工作。

但事实上，这不值得悬赏……

第二次添加

还有一种可能性：

\documentclass[a4paper]{amsbook} % or whatever
\usepackage[T1]{fontenc}
\usepackage{enumitem}
\usepackage{hyperref}

\setlist[enumerate,1]
  {align=left, labelindent=.5em, labelwidth=1.5em}

\begin{document}

Let \( f\colon A\to B \) be a function.  The following are equivalent:
\begin{enumerate}
  \item\label{a}  $f$ is both injective and surjective;
  \item\label{b}  $f$ is invertible.
\end{enumerate}
Proof:
\begin{enumerate}
  \item[$\mbox{(\ref{a})}\Rightarrow\mbox{(\ref{b})}$:]
    Pick an element \( b\in B \), and let \( a\in A \) be the unique element 
    that is sent into~$b$ by~$f$\ldots
  \item[$\mbox{(\ref{a})}\Rightarrow\mbox{(\ref{b})}$:]
    Lorem ipsum dolor sit amet consectetur adipisci elit iam 
    fugiaet enim duscula.  Reprivit ursula tum donec.
\end{enumerate}

\end{document}

这是输出 #3：第三个示例代码的输出

Answer