Creating duplicate numbering for theorems

Question

A conference I publish at has a strange requirement. In the first X pages (X is not important here), we are required to provide an extended abstract of the work, and then after that, we must attach a complete version of the paper with no page limit (the reason is so that reviewers can read the first X pages, and only peruse the rest if they see fit).

One solution is to prepare the full version, make a PDF, prepare the short version, and then use pdfpages to merge the two pdfs together. This is fine, except that if in the process of creating the short version I decided to remove a lemma, then the lemma numbers are not consistent between the short and long versions.

So my question is this: Is there any way to create the desired "double" version so that lemma numbers are consistent between short and long versions ?

We can assume that the lemmas/theorems in the short version are a subset of those in the long version for simplicity. I should note that "lemma" is a set denoting "lemma, theorem, conjecture, corollary, definition" and so on, so all such numberings should remain consistent.

Answer 1

Here is a proposal to solving your problem. The short-version of your article would have the same environments as in the long-version, with an additional optional argument. The optional argument is the long-version label (referenced as an external file via the xr package). This argument is assigned to the short-version environment counter to correct for removal of similar previous environments.

Consider, for example, this is your long-version article (called long-article.tex, say):

\documentclass{article}
\usepackage{lipsum,ntheorem}%
\newtheorem{theorem}{Theorem}% Theorems
\newtheorem{lemma}{Lemma}% Lemmas
\newtheorem{proposition}{Proposition}% Propositions
\begin{document}
  \section{Introduction} \lipsum[1]
    \begin{theorem} \lipsum[2] \label{thm:first} \end{theorem}
    \begin{lemma} \lipsum[3] \label{lem:first} \end{lemma}
  \section{Definitions} \lipsum[4]
    \begin{theorem} \lipsum[5] \label{thm:second} \end{theorem}
    \begin{proposition} \lipsum[6] \label{pro:first} \end{proposition}
  \section{Methodology} \lipsum[7]
    \begin{theorem} \lipsum[8] \label{thm:third} \end{theorem}
    \begin{proposition} \lipsum[9] \label{pro:second} \end{proposition}
    \lipsum[10]
    \begin{lemma} \lipsum[11] \label{lem:second} \end{lemma}
  \section{Conclusions} \lipsum[12]
    \begin{theorem} \lipsum[13] \label{thm:fourth} \end{theorem}
\end{document}

Now you create a short-version article (called short-article.tex, say):

\documentclass{article}
\usepackage{lipsum,ntheorem,xr,ifmtarg}

\newtheorem{shorttheorem}{Theorem}% Theorems
\newtheorem{shortlemma}{Lemma}% Lemmas
\newtheorem{shortproposition}{Proposition}% Propositions
\externaldocument[long-]{long-article}% Long-version article

% (SHORT) Theorem definitions
\makeatletter
\newenvironment{theorem}[1][]% Short-version theorems
  {\@ifnotmtarg{#1}{%
    \setcounter{shorttheorem}{\ref{#1}}%
    \addtocounter{shorttheorem}{-1} \vspace{-\baselineskip}}%
   \begin{shorttheorem}}%
  {\end{shorttheorem}}%
\newenvironment{lemma}[1][]% Short-version lemmas
  {\@ifnotmtarg{#1}{%
    \setcounter{shortlemma}{\ref{#1}}%
    \addtocounter{shortlemma}{-1} \vspace{-\baselineskip}}%
   \begin{shortlemma}}%
  {\end{shortlemma}}%
\newenvironment{proposition}[1][]% Short-version propositions
  {\@ifnotmtarg{#1}{%
    \setcounter{shortproposition}{\ref{#1}}%
    \addtocounter{shortproposition}{-1} \vspace{-\baselineskip}}%
   \begin{shortproposition}}%
  {\end{shortproposition}}%
\makeatother
\begin{document}
  \section{Introduction} \lipsum[1]
    \begin{theorem} \lipsum[2] \label{thm:first} \end{theorem}
    %\begin{lemma} \lipsum[3] \label{lem:first} \end{lemma}
  \section{Definitions} \lipsum[4]
    \begin{theorem} \lipsum[5] \label{thm:second} \end{theorem}
    \begin{proposition} \lipsum[6] \label{pro:first} \end{proposition}
  \section{Methodology} \lipsum[7]
    %\begin{theorem} \lipsum[8] \label{thm:third} \end{theorem}
    \begin{proposition} \lipsum[9] \label{pro:second} \end{proposition}
    \lipsum[10]
    \begin{lemma}[long-lem:second] \lipsum[11] \label{lem:second} \end{lemma}
  \section{Conclusions} \lipsum[12]
    \begin{theorem}[long-thm:fourth] \lipsum[13] \label{thm:fourth} \end{theorem}
\end{document}

You only need to add an optional reference argument to those environments following a removed one ('lemma' and 'theorem' in the above example).

I am not sure why additional (vertical) space was added after executing the \setcounter and \addtocounter commands. However, that's why a negative \baselineskip was added to correct for this behaviour.