1. Cartan, E.: Sur la connexion affine des surfaces. C.R. Acad. Sci. Paris178, 242?245 (1924)
2. Kobayashi, S., Nomizu, K.: Foundations of differential geometry, Vol. II. New York: John Wiley 1969
3. Kulkarni, R.S.: On the principle of uniformization. J. Differ. Geom.13, 109?138 (1978)
4. Nomizu, K.: On completeness in affine differential geometry. Geom. Dedicata20, 43?49 (1986)
5. Nomizu, K., Pinkall, U.: On a certain class of homogeneous projectively flat manifolds, SFB/MPI Preprint 85/44; to appear in T�hoku Math. J.