Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
335144.pdf (Publisher version), 3MB
Ehlers, J., & Schild, A. (1973). Geometry in a manifold with projective structure. Communications in Mathematical Physics, 32(2), 119-146. doi:10.1007/BF01645651.