\documentclass{amsart}\usepackage[all, ps]{xy}% Loading the XY-Pic package% Using postscript driver for smoother curves\usepackage{color}% For invisible frame\begin{document}\thispagestyle{empty}% No page numbers\SelectTips{eu}{}% Euler arrowheads (tips)\setlength{\fboxsep}{0pt}% Frame box margin{\color{white}\framebox{{\color{black}$$% Frame for margin\xymatrix@=6pt{&\{\pm1\}\ar@{^(->}@/_1pc/[ddl]\ar@{_(->}@/^1pc/[ddr]\\\\2\cdot A_n \ar@{->>}[dd]\ar@{^(->}[rr] &&\operatorname{Spin}(n-1)\ar@{->>}[dd]\\ &&\\ A_n \ar@{^(->}[rr] &&\operatorname{SO}(n-1)}$$}}}% end math, end frame\end{document}
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