No fast food for solving higher curvature gravity
  This paper is withdrawn because it was already known in the literature that the single function metric ansatz invalidates the effective action method. (Refs: gr-qc/0306114, gr-qc/0408067,gr-qc/0404120, gr-qc/0506014, 0705.1669, thanks to S. Deser for providing the information.) 
Liu Zhao
gr-qc