标记并引用代表语句的符号？

Question

例如，假设A \iff B \iff C。有什么方法可以为每个符号加上数字（如方程式编号）\iff，并给它们贴上标签，以后再分别引用它们？

Answer 1

更新：经过一番探索后，它现在可以与旧的\ref兼容hyperref（避免在标签内使用，equation因为\refstepcounter弄乱了标签计数器）

\documentclass{article}
\usepackage{mathtools}
\usepackage{hyperref}

\makeatletter
\newcounter{iffcount}
\@ifpackageloaded{hyperref}{
    \newcommand{\liff}[1]{
        \refstepcounter{iffcount}
        \def\Hy@AnchorName{iff.\theiffcount}
        \underset{(\theiffcount)}{\iff}
        \newcounter{#1}
        \setcounter{#1}{\theiffcount}
        \@bsphack    
        \protected@write\@auxout{}{%
            \string\newlabel{#1}{{\theiffcount}{\thepage}{}{\Hy@AnchorName}{}}%
        }%
        \@esphack
        \hyper@@anchor{\Hy@AnchorName}{\relax}%
    }
}{
    \newcommand{\liff}[1]{
        \refstepcounter{iffcount}
        \underset{(\theiffcount)}{\iff}
        \newcounter{#1}
        \setcounter{#1}{\theiffcount}
        \@bsphack
        \protected@write\@auxout{}%
            {\string\newlabel{#1}{{\@currentlabel}{\thepage}}}%
        \@esphack
    }
}
\makeatother

\begin{document}
I claim that \[A\liff{iff:1} B\liff{iff:2} C.\]

I am going to prove \ref{iff:1} here, and prove \ref{iff:2} there.

I also claim that \[C\liff{iff:3} D\liff{iff:4} E.\]

I am going to prove \ref{iff:3} here, and prove \ref{iff:4} there.
\end{document}

结果：

---

旧版本： 这是一个粗略的做法......（不支持hyperref！）

\documentclass{article}
\usepackage{mathtools}

\newcounter{iffcount}
\setcounter{iffcount}{1}
\newcommand{\liff}[1]{
    \underset{(\theiffcount)}{\iff}
    \newcounter{#1}
    \setcounter{#1}{\theiffcount}
    \stepcounter{iffcount}
}
\newcommand{\riff}[1]{\arabic{#1}}

\begin{document}
I claim that \[A\liff{iff:1} B\liff{iff:2} C.\]

I am going to prove \riff{iff:1} here, and prove \riff{iff:2} there.

I also claim that \[C\liff{iff:3} D\liff{iff:4} E.\]

I am going to prove \riff{iff:3} here, and prove \riff{iff:4} there.
\end{document}

结果：