\documentclass{amsart} \usepackage{amsmath,amssymb,nopageno} \usepackage[all]{xy} \begin{document}  \begin{equation*}   \xymatrix@R+2em@C-1em{    & N \ar[dl]_*{\psi_X} \ar[dr]^*{\psi_Y} & \\    F(X) \ar[rr]_*{F(f)} & & F(Y)   }  \end{equation*} \end{document} 

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