 It is clear that any world which contains G-chains rather than H-chains does not show the same inconsistency as Mellor’s G&amp;H-world does. If it can be proved that causal loops in such worlds are consistent with the adopted definition, then causal loops are possible. In other words, if we set up a consistent model in which \(A\) increases the probability of \(B\), and \(B\) increases the probability of \(A\), we have then proven that causal loops are possible and that Mellor’s argument is invalid. The claim is therefore that both