Perlick, Volker Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
3367.pdf (Preprint), 297KB
Chrobok, T., & Perlick, V. (2001). Classification of image distortions in terms of Petrov types. Classical and Quantum Gravity, 18(15), 3059-3079.