 Each world \(w\) has its set \(\textrm{T}_w\) of true propositions, and we call \(\TS(p)\) (the truth-set of \(p\)) the set of all worlds at which \(p\) is true. Where \(p\) is a proposition, let \(\ES(p)\) (the existence-set of \(p\)) be the set of all worlds at which it exists.