# [Xy-pic] Really strange behavior

Michael Barr barr at math.mcgill.ca
Mon Jul 28 17:05:43 CEST 2014

Can anyone explain this behavior?  Compile this:

\documentclass{article}
\pdfoutput1
\usepackage[all]{xy}
\begin{document}
$$\xy \POS(0,0)*+!!<0ex,0ex>{A}\ar^{f}(20,20)*+!!<0ex,0ex>{B}{} \POS(0,0)*+!!<0ex,0ex>{A}\ar^{f}(20,20)*+!!<0ex,0ex>{B} \endxy$$

This doesn't happen if you remove the pair of braces at the end of the
first line.
\end{document}