只需支撑即可array
。
\documentclass{article}
\usepackage[all,cmtip]{xy}
\begin{document}
\xymatrix{
{\begin{array}{@{}c@{}}K_0(M_p\oplus M_q)\oplus{}\\ K_0(C([0,1]),M_p\oplus M_q))\end{array}}
\ar[r] & \\
K_0(Z_{pq}) \ar[u]^{K_0(\pi_1)\oplus K_0(\pi_2) } \\
\ar[u]
}
\end{document}