1. V. de Alfaro and A. T. Filippov, “Integrable low dimensional models for black holes and cosmologies from high dimensional theories,” hep-th/0504101 (2005).
2. D. Grumiller, W. Kummer, and D. Vassilevich, Phys. Rep., 369, 327 (2002); hep-th/0204253 (2002).
3. P. Szekeres, J. Math. Phys., 13, 286 (1972).
4. A. T. Filippov and V. G. Ivanov, Phys. Atomic Nuclei, 61, 1639 (1998); hep-th/9803059 (1998).
5. H. Bateman, The Mathematical Analysis of Electrical and Optical Wave-Motion on the Basis of Maxwell's Equations, Dover, New York (1955).