# [texhax] Theorem numbering

Uwe Lueck uwe.lueck at web.de
Mon Sep 13 21:57:11 CEST 2010

This may be one of the rather serious contributions of mine:

Barbara Beeton <bnb at ams.org>, 04.06.2010 15:34:59:
> stefan witzel asks for the ability to
> "re-use" a theorem with the same number
> as the original.
[...]
> re-using the theorem text is
> left as an exercise for the reader.

Actually doing the exercise:

I thought of the extract' package (ctan.org/pkg/extract) or some
verbatimwrite' (ctan.org/pkg/moreverb,
quite a few packages have similar functions)—difficult
to learn—more easy instead (although not tested, sorry):
Type theorem body code in an extra file, say, thm-outs.tex.
To typeset the theorem at its "proper" place, type

\begin{thm}\label{thm:outs}
\input{thm-outs}
\end{thm}

Barbara’s xrefthm is enlightening,
yet I would prefer the following generalization
(in the document preamble—once I desired to have this!
e.g.: Thm. 2* an “analogue” of Thm. 2 for a different setting):

\newenvironment*{var-id-thm}[1]{%
\def\thethmid{#1}%
\begin{the-var-id-thm}%
}{%
\end{the-var-id-thm}%
}
\newtheorem*{the-var-id-thm}{Theorem \thethmid}

To be used like this:

\begin{var-id-thm}{\ref{thm:outs}}
\input{thm-outs}
\end{var-id-thm}

I prepared the previous as HTML (looks finer) at

http://www.webdesign-bu.de/uwe_lueck/texhax.htm#reuse-thm

(you may find an older version with some mistakes).

Cheers,

Uwe.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[OP:]
>    I'm using the amsthm-Package and number my theorem within sections, i.e.
>
>    \newtheorem{thm}{Theorem}[section]
>
>    Now I would like to quote a theorem from the end of the paper in the
>    introduction with its original number (which is 9.1 in my case).
>    Of course I could do so by manually setting the counters:
>
>    \setcounter{section}{9}
>    \setcounter{thm}{0}
>    \begin{thm}
>    ...
>    \end{thm}
>    \setcounter{section}{1}
>    \setcounter{thm}{0}
>
>    but this destroys the idea of automatic numbering, because if my
>    theorem becomes Theorem 9.2 because it is preceded by Lemma 9.1, it
>    has the wrong number in the introduction.
>    When I once had the problem of quoting a theorem *after* it had been
>    stated, I used the following makros the save and recover the counters:
>
>    [...]
>
>    But how can I can obtain the number before the actual statement (using
>    the \label)? I imagine there should exist solutions to this, but I did
>    not find them on the web (and I don't know enough about
>    makro-programming, to extract the necessary information from the
>    \label-data myself). Many thanks in advance!
>
>the test file attached below uses \label
>to identify the theorem number, and also
>allows for multiple "re-used" theorem
>numbers.  re-using the theorem text is
>left as an exercise for the reader.
>						-- bb
>
>			--------------------
>
>\documentclass{article}
>\usepackage{amsthm}
>
>\newtheorem{thm}{Theorem}[section]
>\newenvironment{xrefthm}[1]{%
>  \def\thexref{\ref{#1}}
>  \begin{thexrefthm}
>}{%
>  \end{thexrefthm}
>}
>\newtheorem*{thexrefthm}{Theorem \thexref}
>
>\begin{document}
>
>\section{Introduction}
>In this section we have two theorems.
>
>\begin{thm}
>The first is an ordinary theorem.
>\end{thm}
>
>\begin{xrefthm}{laterthm}
>The other is a duplicate of a theorem in a later
>section, with its original number.
>\end{xrefthm}
>
>\section{Next}
>Here we have a different forward referenced'' theorem.
>
>\begin{xrefthm}{another}
>This theorem also has a number from a later section.
>\end{xrefthm}
>
>\setcounter{section}{8}
>\section{Ninth}
>
>In this section we have three theorems.
>
>\begin{thm}
>The first is an ordinary theorem.
>\end{thm}
>
>\begin{thm}\label{laterthm}
>But this one will be referenced earlier in the
>paper with the theorem number from here.
>\end{thm}
>
>\begin{thm}\label{another}
>And this one will also be referenced earlier
>with its own number.
>\end{thm}
>
>\end{document}
>_______________________________________________