References
- J. K. Beem, P. E. Ehrlich, and K. L. Easley, Global Lorentzian Geometry, Second edition. Monographs and Textbooks in Pure and Applied Mathematics, 202. Marcel Dekker, Inc., New York, 1996
- U-Hang Ki and J. S. Pak, Projective Geometry, Hak-Moon Sa Press, Seoul, 1982
- H. Nakagawa, J.-H. Kwon, and Y.-S. Pyo, Introduction to Semi-Riemannian geometry, Kyung Moon Publishers, Seoul, 2000
- B. O'Neill, Semi-Riemannian Geometry, Pure and Applied Mathematics, 103, Academic Press, Inc. [Harcourt Brace Jovanovich, Publishers], New York, 1983