\xymatrix@!0{ & \lambda \omega \ar@{-}[rr] \ar@{-}[dd]|!{[dl];[dr]}\hole && \lambda C \ar@{-}[dd] \\ \lambda 2 \ar@{-}[ur] \ar@{-}[rr] \ar@{-}[dd] && \lambda P2 \ar@{-}[ur]\ar@{-}[dd] \\ & \lambda \underline\omega \ar@{-}[rr]|!{[ur];[dr]}\hole && \lambda P \underline\omega \\ \lambda{\to} \ar@{-}[rr] \ar@{-}[ur] && \lambda P \ar@{-}[ur] }