3. We prove an upper bound, suggested in [3], on the free energy of a connected static black hole in terms of the genus of the horizon, cf. Equation (VIII.5) below.When Λ is positive we review the argument of [2] (compare [4]), that the identity mentioned above provides a simple proof of an upper bound for entropy of horizons, Equation (IX.10) below. This upper bound has been rediscovered in [5,6], with different proofs.This work can be thought-of as a continuation of [7]. It reviews, in a slightly different manner, some results from [7] and considers further applications. Similar ideas have been independently pursued in [8].
II. THE EQUATIONSWe consider the vacuum Einstein equations with a cosmological constant Λ for a static spacetime metric which we denote byḡ:ḡ(II.1)We always assume that V ≡ 0 and that (M, g) is complete, possibly with boundary. We shall say that (M, g, V ) is strictly static if V > 0 on M .