\documentclass{article}
\usepackage{xy}
\xyoption{all}
\begin{document}
\pagestyle{empty}
\[
\xymatrix{
B \otimes B \ar[r]^\nabla \ar[d]_{\Delta \otimes \Delta} & B \ar[r]^\Delta & B \otimes B \\
B \otimes B \otimes B \otimes B \ar[rr]^{\mbox{id} \otimes \tau \otimes \mbox{id}} & & B \otimes B \otimes B \otimes B \ar[u]_{\nabla \otimes \nabla}
}
\]
\end{document}
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This image is a derivative work of the following images:
2006-07-28T09:36:40Z Secular mind 426x103 (2584 Bytes) {{Information| |Description= == Summary == Created by Dave Rosoff using LaTeX2e and textogif. |Source= |Date= |Author=User [[:en:User:Alodyne|Alodyne]] on [http://en.wikipedia.org en.wikipedia] |Permission={{PD-self}} |other_
{{Information |Description=== {{int:filedesc}} == Created by Dave Rosoff using LaTeX2e and textogif. |Source=*File:Bialgebra2.png |Date=2010-08-23 06:09 (UTC) |Author=*File:Bialgebra2.png: User Alodyne on [http://en.wikipe