# Why does $\overbrace{\star\star}^{m}$ cause a double superscript error?

In part of my HW paper I have:

$\overbrace{\star\star}^{m}$


This causes the following error:

! Double superscript.
\star ->^
*
l.153          $\overbrace{\star\star} ^{m}$


If I change the line to $\overbrace{\star}^{m}$ it works fine. Why does the double \star\star cause the double superscript error, and how to fix it?!

FYI, This is what I'm trying to recreate:

• Did you forget a begin{document} before it? – Jesse Aug 31 '13 at 2:21
• Nope...The template file that I'm using was given to us by the professor, so all the boilerplate is there. These are the packages that are being used: \usepackage{fullpage} \usepackage{amsmath,amsfonts,enumerate,amsthm} \usepackage{zed-csp}. – rishimaharaj Aug 31 '13 at 2:24
• The problem is with the zed-csp package. It defines \star as ^* – A.Ellett Aug 31 '13 at 2:26
• By the way, the symbol in your image is \ast, not \star. – Gonzalo Medina Aug 31 '13 at 2:28

Your problem is arising because of the zed-csp file which redefines \star as

\def\star{^*}


If you feel you must use the zed-csp package, then before calling this package you can write:

\usepackage{amsmath}
\let\oldstar\star
\usepackage{zed-csp}


Then later you should be able to write

$\overbrace{\oldstar\oldstar}^{m}$


However, it seems from the image you've posted it is \ast that you want to use instead of \star.

If you decide you do not intend to use the redefined \star from the zed-csp package you can do something like the following:

\documentclass{article}
\usepackage{amsmath,amssymb}
\let\oldstar\star
\usepackage{zed-csp}
\let\zedstar\star
\let\star\oldstar

\begin{document}

$\overbrace{\star\star}^{m}$

\end{document}

• Awesome! I think in future classes we will need zed-csp, so I just replaced all \star with \ast and everything is perfect. I will accept this as the answer when the system allows me to. – rishimaharaj Aug 31 '13 at 2:39