反向计数

Question

我想找到一个解决方案来生成像这样的反向计数的项目

4. 啦啦啦
5. 啦啦啦
6. 啦啦啦

Answer 1

也许像这样的事情可以解决问题——它至少需要两次编译才能解决：

\documentclass{article}
\usepackage[colorlinks=true]{hyperref}
\usepackage[user]{zref}

\makeatletter
\zref@newprop{ItemNo}{}%
\newcommand\my@caseselect[2]{#2}%
\newcommand\ItemNumberlabel[1]{%
  \bsphack
  \begingroup
  \let\my@caseselect=\@firstoftwo
  \zref@setcurrent{ItemNo}{\number\value{enum\romannumeral\@enumdepth}}%
  \zref@labelbyprops{#1}{ItemNo}%
  \endgroup
  \esphack
}%
\newcommand\revertcounting[2]{%
  \expandafter\@revertcounting
  \expandafter{\romannumeral\the\numexpr\@enumdepth+1\expandafter\relax\expandafter}%
  \expandafter{\romannumeral\the\@enumdepth}%
  {#1}{#2}%
  \ignorespaces
}%
\newcommand\@revertcounting[4]{%
  \@namedef{theenum#1}{%
    \my@caseselect{%
      \csname @#4\endcsname{\csname c@enum#1\endcsname}%
    }{%
      \zref@ifrefundefined{#3}%
                          {\csname @#4\endcsname{\csname c@enum#1\endcsname}}%
                          {%
                             \csname @#4\endcsname{%
                               \the\numexpr
                                  \zref@extractdefault{#3}{ItemNo}{0} - %
                                  \number\value{enum#1} + 1%
                                \relax
                             }%
                          }%
    }%
  }%
}%
\makeatother

\begin{document}

\null\par\kern-3cm

\begin{enumerate}
\item text A
\item text B
\item
\begin{enumerate}
\item text One
\item \label{itA}text Two
\item text Three
\item text Four
\end{enumerate}
\item text D
\end{enumerate}

\bigskip\hrule\bigskip

\begingroup
\revertcounting{lastitemA}{arabic}%
\begin{enumerate}
\item text A
\item text B
\item
\begingroup
\revertcounting{lastitemB}{alph}%
\begin{enumerate}
\item text One
\item \label{itB}text Two
\item text Three
\item \ItemNumberlabel{lastitemB}text Four
\end{enumerate}
\endgroup
\item \ItemNumberlabel{lastitemA}text D
\end{enumerate}
\endgroup

\bigskip\hrule\bigskip

\begingroup
\revertcounting{lastitemC}{arabic}%
\begin{enumerate}
\item text A
\item text B
\item
\begin{enumerate}
\item text One
\item \label{itC}text Two
\item text Three
\item text Four
\end{enumerate}
\item \ItemNumberlabel{lastitemC}text D
\end{enumerate}
\endgroup

\bigskip\hrule\bigskip

\begin{enumerate}
\item text A
\item text B
\item
\begingroup
\revertcounting{lastitemD}{alph}%
\begin{enumerate}
\item text One
\item \label{itD}text Two
\item text Three
\item \ItemNumberlabel{lastitemD}text Four
\end{enumerate}
\endgroup
\item text D
\end{enumerate}

Cross-referencing:

\verb|\ref{itA}|: \ref{itA}

\verb|\ref{itB}|: \ref{itB}

\verb|\ref{itC}|: \ref{itC}

\verb|\ref{itD}|: \ref{itD}

\end{document}