Distilling a Greenberger-Horne-Zeilinger State From an Arbitrary Pure   State of Three Qubits
  We present a general algorithm to achieve local operators which can produce the GHZ state for an arbitrary given three-qubit state. Thus the distillation process of the state can be realized optimally. The algorithm is shown to be sufficient for the three-qubit state on account of the fact that any state for which this distillation algorithm is invalid cannot be distilled to the GHZ state by any local actions. Moreover, an analytical result of distillation operations is achieved for the general state of three qubits. 
Li-Xiang Cen, Shun-Jin Wang