1. Cartan, E.: Sur une classe remarquable d’espaces de Riemann. Bull. Soc. Math. France 54, 214–264 (1926)
2. Szaó, Z. I.: Structure theorems on Riemannian spaces satisfying $$R(X, Y).R= 0$$. Geometriae Dedicata. 19, 65–108 (1985)
3. Sen, R.N., Chaki, M.C.: On curvature restrictions of a certain kind of conformally flat Riemannian space of class one. Proc. Nat. Inst. Sci. India 33, 100–102 (1967)
4. Chaki, M. C.: On pseudo symmetric manifolds. An. Stiint. Univ. Al. I. Cuza Iasi Sect. I a Mat. 33, 53–58 (1987)
5. Chaki, M.C.: On pseudo Ricci symmetric manifolds. Bulg. J. Phys. 15, 526–531 (1988)