 We shall say that a set of facts \(G\) characterizes a set of worlds \(V\) iff \(\CES(G) = V\), and that a fact \(x\) characterizes a set of worlds \(V\) iff \(\ES(x) = V\) (no confusion should arise from the ambiguity of ‘characterize’). At this very early point some work can already be done.