Repeat an enumerate list in different order - an enumitem question

Question

I want an enumerate list be repeated in a different order (for example, a list of two statements and later a list of two proofs: first the second statement proof and then the first statement proof). I expected that the following code would do this, but in some reason it just produces a regular list with "0" strings.

Please help to find and correct my error.

\documentclass[english]{article}

\usepackage{enumitem}
\setlist[enumerate,1]{label=\arabic*$^\circ$.,ref=\arabic*$^\circ$}

\newlist{enumeratex}{enumerate}{5}
\setlist[enumeratex]%
{label=\arabic*$^\circ$.,%
before={\let\olditem=\item\renewcommand\item[1][]{\olditem[#1.]}},%
after={\let\item=\olditem}}

\begin{document}

\begin{enumerate}
  \item \label{a} a
  \item \label{b} b
\end{enumerate}

into

\begin{enumeratex}
  \item[\ref{b}] proof of b
  \item[\ref{a}] proof of a
\end{enumeratex}


\end{document}

The desired output is:

Optionally, I want the second list labels to be hyperlinks to first list labels.

Answer 1

Here is an adaptation of Optional argument to \item to appear in brackets after the counter for your case:

Notes:

• If you wish to redefine a macro that has optional parameters, you have to use \LetLtxMacro from the letltxmacro package . A detailed description of \LetLtxMacro can be found at this question at When to use \LetLtxMacro?.

Code:

\documentclass{article}

\usepackage{enumitem}
\usepackage{letltxmacro}


\setlist[enumerate,1]{label=\arabic*$^\circ$.,ref=\arabic*$^\circ$}

\LetLtxMacro{\OldItem}{\item}

\newcommand*{\LabelText}{}%
\newcommand*{\MyItem}[1][]{%
    \renewcommand{\LabelText}{#1}\OldItem\leavevmode%
}%

\newlist{enumeratex}{enumerate}{5}
\setlist[enumeratex]%
{label=\noexpand\LabelText.,%
before={\let\item\MyItem},%
after={\let\item\OldItem}}

\begin{document}

\begin{enumerate}
  \item \label{a} a
  \item \label{b} b
\end{enumerate}

into

\begin{enumeratex}
  \item[\ref{b}] proof of b
  \item[\ref{a}] proof of a
\end{enumeratex}

\end{document}