An Introduction to Einstein's General Relativity
James B. Hartle
Web Supplements are extensions of the exposition in various chapters in the text. They typically are concerned with technical developments or with ideas which are conceptually simple but require lengthy derivations whose inclusion in the text would have been a significant interruption in its flow. For instance, on p. 174 the text mentions that a general formula for the Christoffel symbols in terms of the metric (8.19) can be derived by working out Lagrange's equations for the Lagrangian (8.10) that summarizes the idea that a geodesic is a curve of extremal proper time. The first Web Supplement gives this derivation.