1. BLAIR D.E.:Contact Manifolds in Riemannian Geometry, Lect. Notes Math. 509, Berlin, Springer, 1976.
2. BLAIR D.E.:When is the tangent sphere bundle locally symmetric?, Geometry and Topology, World Scientific, Singapore, 1989, 15?30.
3. CARPENTER P., GRAY A., WILLMORE T. J.:The curvature of Einstein symmetric spaces, Quart. J. Math. Oxford (2),33 (1982), 45?64.
4. CARTAN E.:Geometry of Riemannian Spaces, Math. Sci. Press, Brookline Mass., 1983.
5. CHEN B.Y., VANHECKE L.:Differential geometry of geodesic spheres, J. Reine Angew Math.325 (1981), 28?67.