1. Besse, A. L.: Manifolds all of Whose Geodesics are Closed. Berlin-Heidelberg-New York: Springer. 1978.
2. Chen, B. Y.: Geometry of Submanifolds. New York: Marcel Dekker. 1973.
3. Chen, B. Y., Vanhecke, L.: Differential geometry of geodesic spheres. J. Reine Angew. Math.325, 28?67 (1981).
4. Djori?, M., Vanhecke, L.: Almost Hermitian geometry, geodesic spheres and symmetries. To appear.
5. Ledger, A. J., Vanhecke, L.: Symmetries and locallys-regular manifolds. Ann. Global Anal. Geom.5, 151?160 (1987).