1. Belkhelfa, M.: Differential Geometry of Semi-Riemannian Manifolds and Submanifolds. PhD thesis K.U. Leuven (2001)
2. Belkhelfa, M., Deszcz, R., Glogowska, M., Hotloś, M., Kowalczyk, D., Verstraelen, L.: On some type of curvature conditions. In: Banach Center Publ., vol. 57, pp. 179–194, Inst. Math., Polish Acad. Sci. (2002)
3. Belkhelfa M., Deszcz R., Verstraelen L.: Symmetry properties of Sasakian space-forms. Soochow J. Math. 31(4), 611–616 (2005)
4. Blair D.E.: Geometry of manifolds with structural groups $${U(n)\times O(s)}$$ U ( n ) × O ( s ) . J. Differ. Geom. 4, 155–167 (1970)
5. Blair D.E.: On a generalisation of the Hopf fibration. An. Ştiinţ. Univ. Al. I. Cuza laşi. Mat. (N.S.) XVII, 171–177 (1971)