 All the technical material required to delve more deeply into the subject of this entry can be found in any of a number of excellent classic and recent sources, including: Hawking and Ellis (1973); Geroch and Horowitz (1979); Wald (1984, 1994); Brout et al (1995); Malament (2007, 2012); and Manchak (2013). The reader unfamiliar with general relativity may find it helpful to review the Hole Argument entry's  Beginner's Guide to Modern Spacetime Theories,  which presents a brief and accessible introduction to the concepts of a spacetime manifold, a metric, and a worldline. 