# Error when using \bm in *numbered* section title, when hyperref is loaded

I am getting an error when I use the command \bm in a section title that is numbered, when the package hyperref is loaded. Here is the error:

ERROR: TeX capacity exceeded, sorry [input stack size=5000].

--- TeX said --- to be read again>
{ l.10 ...ction{A proof of convexity in $p,\bm{w}$}

and here is the MWE

\documentclass{article}
\usepackage{bm}
\usepackage[bookmarks]{hyperref}

\begin{document}
\section{A proof of convexity in  $p,\bm{w}$}
\end{document}


Note that I can get avoid the error if I do any of the following

• use \section* instead of \section (and this really intrigues me!)
• remove the \bm{} from the title
• remove the package hyperref

I noticed there is a question similar to mine (such as this) but the solution seems not to be related to my problem.

Does anyone know how to solve this?

-
You don't know how to use backticks? –  Who is crazy first Mar 16 '12 at 5:48
@DamienWalters no... I have no idea what you are talking about... Can you explain? –  Vivi Mar 16 '12 at 5:52
Inline codes each should be sandwiched by a pair of backticks. –  Who is crazy first Mar 16 '12 at 6:00
@DamienWalters oh, I see. Yes, I know that... I thought you were referring to some latex backticking. I should have done that, but forgot. Thanks :) –  Vivi Mar 16 '12 at 6:45

The PDF bookmarks can not have formatting, so you can either

1. Use \texorpdfstring within the \section command to provide the alternate text to be used for the bookmakrs:

\section{A proof of convexity in  \texorpdfstring{$p,\bm{w}$}{$p,w$}}

2. Or use \pdfstringdefDisableCommands to disable the macros (thanks to Stephan Lehmke for pointing this out):

\pdfstringdefDisableCommands{%
\renewcommand*{\bm}[1]{#1}%
% any other necessary redefinitions
}


I prefer this approach as it does not clutter up your main text.

## Code: \texorpdfstring:

\documentclass{article}
\usepackage{bm}
\usepackage[bookmarks]{hyperref}

\begin{document}
\section{A proof of convexity in  \texorpdfstring{$p,\bm{w}$}{$p,w$}}
\end{document}


## Code: \pdfstringdefDisableCommands:

\documentclass{article}
\usepackage{bm}
\usepackage[bookmarks]{hyperref}

\pdfstringdefDisableCommands{%
\renewcommand*{\bm}[1]{#1}%
% any other necessary redefinitions
}

\begin{document}
\section{A proof of convexity in  $p,\bm{w}$}
\end{document}

-
That's the second time the solution to my problem is to use \texorpdfstring{}{}! See my other question related to beamer title here: tex.stackexchange.com/q/45938/14 That solves my problem and I am happy, but out of curiosity, do you know why removing the numbering (using \section*) solves the problem? –  Vivi Mar 16 '12 at 5:51
I assume that when you use \section*, then that section is not only not numbered, but it is also not added to the TOC (unless you use \phatomsection), so there is no issue. –  Peter Grill Mar 16 '12 at 5:53