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\Delta \psi + \frac{1}{8} \psi^{-7} \hat{K}_{i j}\hat{K}^{i j} = 0.  \end{equation}  Bowen-York data relates very neatly to the ADM quantities, but has two main disadvantages: (a) the Hamiltonian constraint (\ref{eq:by_ham_const}) must be solved explicitly to obtain a solution of the Einstein equations, and (b) even once solved, the data does {\it not} describe a ``clean'' black hole -- there's always some radiation on top of the hole, which will radiate away to infinity, or into the hole, over time. In contrast, Kerr-Schild data (subsection \ref{sec:ks_general}) represents both spinning and boosted black holes very cleanly.     The real advantage of conformal data like Bowen-York is its convenient extension to multiple black holes. Since the momentum constraint is linear in the extrinsic curvature, the exact B-Y solutions (\ref{eq:by_K_P_S}) can be repeated -- with different $S$ and/or $P$, and centred at a different point in coordinate space -- to represent multiple holes. The number of holes present doesn't affect the only numerical problem, that of solving the Hamiltonian constraint (\ref{eq:by_ham_const}).