How to refer to the number of an item in an enumerate environment inside a theorem

Question

I have something that looks like this:

\usepackage{amsmath}
\begin{document}
\begin{thm}
The following are true:
\begin{enumerate}
\item \label{foo} Foo
\item \label{bar} Bar
\item \label{baz} Baz
\end{enumerate}
\end{thm}

Refer to Theorem \ref{bar}

\end{document}

Right now, the reference to bar shows up as Theorem 1. I want it to show up as Theorem 1.2. Is there any way to do that? To give a sub-numbering to each label within a theorem?

Answer 1

I agree with Jubobs comment: using "Theorem 1.2" is very likely to be confusing.

Here's how one might do:

\documentclass{article}
\usepackage{enumitem}
\newenvironment{thmenum}
 {\begin{enumerate}[label=\upshape(\arabic),ref=\thethm(\arabic)]}
 {\end{enumerate}}
\newtheorem{thm}{Theorem}
\begin{document}
\begin{thm}
The following are true:
\begin{thmenum}
\item \label{foo} Foo
\item \label{bar} Bar
\item \label{baz} Baz
\end{thmenum}
\end{thm}
Refer to Theorem \ref{bar}
\end{document}

I'd give the items a distinctive numbering, so that it will be clearer that "Theorem 1(2)" refers to statement 2 in theorem 1.

Edit for feature request

\documentclass{article}
\usepackage{amsthm}
\usepackage{enumitem}
\NewDocumentCommand{\refprefix}{m}{%
  \ifinproofref\else #1\fi
 }
\newif\ifinproofref
\newcommand{\proofref}[1]{\begingroup\inproofreftrue\ref{#1}\endgroup}
\newenvironment{thmenum}
 {\begin{enumerate}[label=\upshape(\arabic),ref=\refprefix{\thethm}(\arabic)]}
 {\end{enumerate}}
\newtheorem{thm}{Theorem}
\begin{document}
\begin{thm}
The following are true:
\begin{thmenum}
\item \label{foo} Foo
\item \label{bar} Bar
\item \label{baz} Baz
\end{thmenum}
\end{thm}
\begin{proof}
\proofref{foo} is easy. \proofref{bar} is not difficult and 
immediately proves also~\proofref{baz}.
\end{proof}
Refer to Theorem~\ref{bar}
\end{document}

The format of the ref is made so \thethm can be omitted. You have to use \proofref when referring to the item.