1. Misner, C.W. and Wheeler, J.A. (1957). Classical Physics as Geometry,Ann. Phys.,2, 525?603; (reprinted in: Wheeler, J.A. (1962).Geometrodynamics, (Academic Press, New York).
2. Misner, C.W., Thorne, K.S. and Wheeler, J.A. (1973).Gravitation, (W.H. Freeman and Company, San Francisco).
3. Landau, L.D. and Lifshitz, E.M. (1962).The Classical Theory of Fields, (transl. Hamermesh, M.), (Addison-Wesley, Reading, Massachusetts).
4. Veblen, O. (1927).Invariants of Quadratic Differential Forms, (Cambridge Tracts, No.24), (Cambridge University Press, Cambridge).
5. Israel, W. (1968). Event Horizons in Static Electrovac SpaceTimes,Commun. Math. Phys.,8, 245?260.