# [texhax] Strange interaction with revtex

Michael Barr barr at math.mcgill.ca
Sat Aug 14 21:47:00 CEST 2010

I got a query from someone trying to use my diagram macros in conjunction
with revtex.  Finally, I decided to try to track it down.  What follows is
really strange and I could not begin to imagine how it could be done.
Here is a sample file:

\documentclass{revtex4}
\newdimen\ul
\ul=.01em
\showthe\ul
\begin{document}
\end{document}

Try it; you get the message that \ul=0pt.  If you put it after the
\begin(document} you get the correct value.  How can this be done?  Lest
you answer that I should not be using \newdimen, I point out that the
diagram macros work fine with plain tex (and anything else I have tried
them with).  Of course, \ul is a basic dimension in them.

Can anyone explain what is going on?

Update: I tried changing \ul to \UL in the above file and the results were
the same.  If I changed em to ex, same result.

Michael