1. Horsky, J. (1968).Czechoslovak Journal of Physics,B18, 569?583.
2. Ipser, J., and Sikivie, P. (1984).Physical Review D,30, 712?719.
3. Ipser, J. (1984).Physical Review D,30, 2452?2456.
4. Kibble, T. W. B. (1976).Journal of Physics,A9, 1387?1398.
5. Kramer, D., Stephani, H., Herlt, E., and MacCallum, M. (1980).Exact solutions of Einstein's Field Equations, p. 161. Cambridge University Press, Cambridge, England.