1. C.W. Misner, K.S. Thorne, J.A. Wheeler, Gravitation (W. H. Freeman and Company, New York, 1973)
2. R. D’Inverno, Introducing Einstein’s Relativity (Oxford University Press, Oxford, 1998)
3. A.R. Liddle, An Introduction to Modern Cosmology (Wiley & Sons, Chichester, 2015)
4. A.R. Liddle, D.H. Lyth, Cosmological Inflation and Large-Scale Structure (Cambridge University Press, Cambridge, 2000)
5. See for instance: C.W. Misner, Astrophys. J. 151, p. 431 (1968)