Using todonotes in math-mode

Question

Is it possible to create notes via the package todonotes in a displayed math environment? Here is a minimal example where it fails:

\documentclass{minimal}

\usepackage{todonotes}

\begin{document}
\[
\todo{think about it twice}foo = bar
\]
\end{document}

Anyone an idea?

Answer 1

The todo note needs to be added to material in the vertical list that (La)TeX is building. You can use \vadjust to add such material when in other contexts. So the following produces the desired result:

\documentclass{article}

\usepackage{todonotes}

\begin{document}

\[
\vadjust{\todo{think about it twice}} x^2 = y^2 + z^2
\]

\end{document}

Note that this will not work with eqnarray nor the ams math environments, whose internals are rather different.