方程标签未在投影仪覆盖（简单列表环境）中解析

Question

将方程式 \label{} 放入列表 \item 中，其中项目将作为覆盖物选择性地显示，似乎会导致 LaTeX 隐藏其自身的引用。这是一个最小工作示例：

\documentclass{beamer}
\begin{document}
\begin{frame}[fragile]
\fontsize{6pt}{7.2}\selectfont
Outside of the \texttt{list} environment (with overlays), there is no
  problem resolving equation number references, e.g.
\texttt{\textbackslash ref\{eq:eq1\}} resolves to eq \ref{eq:eq1}:
\begin{equation}
    x=1
\label{eq:eq1}
\end{equation}
However within a simple list, where an \texttt{\textbackslash item} appears
within an overlay: equation reference labels are not accessible (even
within the overlay itself). See below:
\begin{list}{}{}
\only<1>{\item Item 1: Not very interesting.}
\only<2>{\item Item 2:
\begin{equation}
    x=2
\label{eq:eq2}
\end{equation}
The reference \texttt{\textbackslash ref\{eq:eq2\}} appears unresolved as
eq \ref{eq:eq2}, although eq \ref{eq:eq1} (outside the list) is still
resolved OK.}
\end{list}
\end{frame}
\end{document}

粘贴上述代码并在其上运行 pdflatex，我得到如下输出：

多次重新运行 latex 仍无法解决缺少的引用：日志文件包含：

LaTeX Warning: There were undefined references.

 )pdfTeX warning (dest): name{eq:eq2} has been referenced but does not exist, replaced by a fixed one

还能给我指点一下如何显示这些引用吗？

Answer 1

两种可能性：

1. 正如已经说过的@gernot那样\label<2>{eq:eq2}

2. list首先，您使用有什么特殊原因吗？ Beamer 对itemize环境有很好的支持，即使您不想要 itemize 符号，您也可以这样做：

---

\documentclass{beamer}
\begin{document}
\begin{frame}[fragile]

\begin{equation}
    x=1
\label{eq:eq1}
\end{equation}

\begin{itemize}[<+->]
    \item[] Item 1: Not very interesting.
    \item[] Item 2:
            \begin{equation}
                x=2
            \label{eq:eq2}
            \end{equation}
            \ref{eq:eq2} \ref{eq:eq1}
\end{itemize}

\end{frame}
\end{document}