Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
Ehlers, J., & Kundt, W. (1962). Exact solutions of the Gravitational Field Equations. In L., Witten (Ed.), The Theory of Gravitation (pp. 49-101). New York and London: John Wiley & Sons, Inc.
