1. M. Barros -B. Y. Chen -F. Urbano,Quaternion CR-submanifolds of quaternion manifolds, Kodai Math. J.,4 (1981), pp. 399–417.
2. M.Berger,Sur les variétés compactes, C. R. III Réunion Math. Expression Latine, Namur, (1965), pp. 35–55.
3. W. M. Boothby,An introduction to differentiable manifolds and Riemannian geometry. Academic Press, New York, 1975.
4. E. Cartan,Sur des familles remarquables d'hypersurfaces isoparametriques dans les espaces sphériques, Math. Zeit.,45 (1939), pp. 335–367.
5. T. E. Cecil -P. J. Ryan,Focal sets and real hypersurfaces in complexprojective space, Trans. Amer. Math. Soc.,269 (1982), pp. 481–499.