 We then define the domain \(F_w\) of world \(w\) to be the set of all facts \(w\) contains. Thus the union of all the domains is the set of all facts. Clearly, each world belongs to its own domain and to it only: \(\ES(w) = \{w\}\). So (as we previously pointed out) No Twins and W2 hold, and Modal Criterion is ensured if we accept the principle according to which two facts are identical provided that they are contained in the very same worlds.