1. Burman, R. J.: 1971,Proc. Roy. Soc. New South Wales 104, 1.
2. Ellis, G. F. R.: 1973, in E. Schatzmann (ed.), ?Relativistic Cosmology?,Cargese Lectures in Physics, Gordon and Breach, New York.
3. Lyttleton, R. A. and Bondi, H.: 1959,Proc. Roy. Soc. London A 252, 313.
4. Nduka, A.: 1981,Acta Phys. Pol. B 12, 833.
5. Rao, J. R. and Panda, H. S.: 1975,J. Phys. A 8, 1413.