1. K. Amur, Y. B. Maralabhavi, On quasi-conformally flat spaces, Tensor (N.S.) 31 (1977) 194-198.
2. A. Bhattacharyya, T. De, D. Debnath, Spacetime with generalized covariant recurrent energy momentum tensor, Tamsui Oxford Journal of Mathematical Sciences 25(3) (2009) 269-276.
3. A. L. Besse, Einstein manifolds, Ergeb. Math. Grenzgeb. 3. Folge, Bd. 10. Berlin, Heidelberg, New York: Springer-Verlag (1987).
4. J. K. Beem, P. E. Ehrlich, Global Lorentzian geometry (Marcel Dekker, New York 1981).
5. K. Chattopadhyay, D. Debnath, A. Bhattacharyya, A study of spacetimes with vanishing M-projective curvature tensor, Journal of The Tensor Society of India 12 (2018) 23-31.