1. Seljak U., Zaldarriaga M.: Astrophys. J. 469, 437 (1996)
2. Seljak U., Sugiyama N., White M., Zaldarriaga M.: Phys. Rev. D68, 083507 (2003)
3. Hinshaw, G., et al.: submitted to Astrophys. J. Suppl. Ser. (2008). arXiv:0803.0732 (2008)
4. Ellis G.F.R.: Nature 452, 158 (2008)
5. Ehlers J., Geren P., Sachs R.K.: J. Math. Phys. 9, 1344 (1968)