 The dizzying variety of proofs on offer, which can be roughly classified by how each answers these (and other related) questions, thus prompts the question: what is the relation among all the different principles actually derived by each proof? Do they represent the same physical principle as it manifests itself in different regimes, and as it is viewed from different perspectives? Again, the answer one gives to this question will depend sensitively on, inter alia, one's views on inter-theoretic relations. Indeed, because different answers to these questions can lead to “proofs” that have, respectively, contradictory assumptions, one may well worry that the derived principle, if it is to be the same in all cases, will turn out to be a tautology! 