Source:

%&latex
\documentclass{article}
 \usepackage[matrix,arrow,ps]{xy}
 \pagestyle{empty}

\begin{document}
 \[
 \xymatrix@C+2em{
 A \otimes A \otimes A \ar[r]^{\mu_A \otimes \mathrm{id}_A} \ar[d]_{\mathrm{id}_A \otimes \mu_A}  & 
 A \otimes A \ar[d]^{\mu_A} 
 \\
 A \otimes A \ar[r]^{\mu_A}  & 
 A
 }
 \]
\end{document}

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