1. I. D. Novikov, ?Analysis of the operation of a time machine,? Zh. Éksp. Teor. Fiz.,95, No. 3, 769?776 (1989).
2. D. Cramer, H. Stefani, E. Herlt, and M. MacCullum (eds.), Exact Solutions of the Einstein Equations [Russian translation], Energoizdat, Moscow (1982), p. 96.
3. N. Tarig and B. O. J. Tupper, ?Einstein-Maxwell metrics admitting dual interpretation,? J. Math. Phys.,17, 292?296 (1976).
4. A. V. Levichev, ?Methods of investigating the causal structure of homogeneous Lorentz manifolds,? Sib. Mat. Zh.,31, No. 3, 39?54 (1990).
5. M. A. Ulanovskii, ?Homogeneous Lorentz spaces. I,? Ukr. Geom. Sb (Kharkov), No. 30, 116?122 (1987).