* Gravitation, ISBN 0-7167-0344-0 §31.2 The nonsingularity of the gravitational radius, and following sections; §34 Global Techniques, Horizons, and Singularity Theorems | * Gravitation, ISBN 0-7167-0344-0 §31.2 The nonsingularity of the gravitational radius, and following sections; §34 Global Techniques, Horizons, and Singularity Theorems |