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When using LaTeX for numbered theorems (or other numbered environments for that matter), if you have a theorem, and then you want to give a reformulation of the theorem, is there anyway to get LaTeX to number your first theorem, say Theorem 5, and your reformulation as say Theorem 5'?

To obtain numbered theorems, I am not using any package, just using the command

\newtheorem{theorem}{Theorem}

in my preamble.

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1 Answer 1

up vote 3 down vote accepted

For a one-off use, perhaps the simplest is to say

\addtocounter{theorem}{-1}% so next theorem will be 5 again then
\begingroup% local redefinition of theorem counter printing
\renewcommand\thetheorem{\arabic{theorem}'}
\begin{theorem}...
\end{theorem}
\endgroup

Or for example wrap it in an environment such as

\newenvironment{alttheorem}
{%
 \addtocounter{theorem}{-1}%
 \renewcommand\thetheorem{\arabic{theorem}'}%
 \theorem}
{\endtheorem}

then use an alttheorem environment after a theorem one.

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Thanks for that. Would there be any way to incorporate this into a newly defined environment? –  David Ward Sep 3 '12 at 13:04
    
yes sure (I'll put it in the answer as code formatting in comments is rubish) –  David Carlisle Sep 3 '12 at 13:05
    
Thanks for that. –  David Ward Sep 3 '12 at 13:24
    
Wouldn't it be safer to use \label, \ref just in case the restated theorem is not exactly after the original one? –  Gonzalo Medina Sep 3 '12 at 13:58
1  
@GonzaloMedina It might be although it's a bit harder as by default \ref doesn't necessarily return something locally reusable as \thetheorem (and if you poke at \ref internals you have to be careful not to trip over hyperref which changes them) –  David Carlisle Sep 3 '12 at 14:14

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