Kerr-Schild metrics revisited II. The complete vacuum solution
  The complete solution of Einstein's gravitational equations with a vacuum-vacuum Kerr-Schild pencil of metrics $g_{ab}+V l_al_b$ is obtained. Our result generalizes the solution of the Kerr-Schild problem with a flat metric $g_{ab}$ (represented by the Kerr theorem) to the case when $g_{ab}$ is the metric of a curved space-time. 
L\'aszl\'o \'A. Gergely, Zolt\'an Perj\'es