1. D.V.Anosov, Geodesic flow on closed Riemannian manifolds with negative curvature, Proc. Steklov Inst. Math. 90, 1967 (Amer. Math. Soc. translation, 1969).
2. M. Berger andD. �bin, Some decomposition of the space of symmetric tensors on a Riemannian manifold,J. Diff. Geom. 3 (1969), 379?392.
3. D.E. Blair, Contact manifolds in Riemannian geometry, Lect. Notes in Math.,509, Springer-Verlag, Berlin and New York, 1976.
4. D.E. Blair andH. Chen, A classification of 3-dimensional contact metric manifolds withQ? =?Q, II, Bull. Inst. Math. Acad. Sinica 20 (1992), 379?383.
5. D.E.Blair, Special Directions on Contact metric manifolds of negative ?-sectional curvature,Ann. Fac. Sc. de Toulouse, to appear.