Personalized enumerate working with \label and \ref

Question

Thanks everyone in advance for your help.

I want to create a list of axioms. I want to use labels of the form (An), where n=4 at the beginning and then it increase at each new item. I also want to be able to use \label and \ref to refer back to certain specific axioms. I can get the labels right (but only by brute force). I cannot make \label and \ref working properly though.

It would be great if the result is compatible with \hyperref.

This is the best I could do.

\documentclass[11pt,twoside,a4paper]{article}

\usepackage{enumerate}

\usepackage{hyperref}

\begin{document}

\begin{enumerate}

\item[(A4)]\label{a4} axiom 4

\item[(A5)]\label{a5} axiom 5

\end{enumerate}

\ref{a4}

\end{document}

The problems with this are:

(1) I have to manually insert (A4), etc. at each new item

(2) \ref{a4} does not give (A4).

Thanks again.

Answer 1

There is a way with enumitem:

\documentclass[11pt,twoside,a4paper]{article}

\usepackage{enumitem}

\usepackage[colorlinks]{hyperref}

\begin{document}

\begin{enumerate}[label=\emph{(A\arabic*)}, start=4]

\item\label{a4} axiom 4

\item\label{a5} axiom 5

\end{enumerate}

\ref{a4}

\end{document}

The formatting command \emph can be removed from the reference by option ref:

\begin{enumerate}[
  label=\emph{(A\arabic*)},
  ref=(A\arabic*),
  start=4]