 At least as interesting, from both a physical and a philosophical point of view, is the fact that the Generalized Second Law in fact admits a wide variety of different ways of being proven (Wall 2009). Some of those ways are more mathematically rigorous than others, some more physically perspicuous and intuitive, some more general, and almost all have their respective validity in different regimes than the others, using different types of physical systems, different approximations and idealizations, and different physical and mathematical starting points. “Proofs” have been given, for example, in the classical, hydrodynamic, semiclassical, and full quantum gravity regimes of black holes. 