Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
336807.pdf (Publisher version), 404KB
Ehlers, J., Rindler, W., & Penrose, R. (1965). Energy Conservation as the Basis of Relativistic Mechanics. II. American Journal of Physics, 33(12), 995-997. doi:10.1119/1.1971205.