Two line entry in xymatrix

Question

I would like to create a two-lined entry in my xymatrix. In the attached picture, I want to split the direct sum into two lines.

I tried array but this didn't work.

Thanks !

Answer 1

Just brace the 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}