Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
3375.pdf (Preprint), 352KB
Ehlers, J., & Newman, E. T. (2000). The Theory of Caustics and Wave Front Singularities with Physical Applications. Journal of Mathematical Physics, 41, 3344-3378.