 As we also saw in  §3.3,  CBF entails the principle N that everything (i.e., everything there happens to be) is necessarily identical to something. And, obviously, so too does the full necessitism principle \(\Box\textbf{N}\). But N is clearly invalid in KQML: because world domains can vary, an individual \(a\) in the actual world might not exist in another world, i.e., it might be that nothing is identical to \(a\) in some  worlds.[52]  Hence, since N is invalid in KQML, so are CBF and  \(\Box\textbf{N}\).[53]