 The approach has been generalized to quantified modal logics (Rantala 1982b) and developed into a unified framework for epistemic logics (Wansing 1989, 1990). Wansing has shown that various logics for knowledge and belief developed in Artificial Intelligence can find equivalent models in structures including impossible worlds. Further equivalence results in this area have been obtained in Sillari 2008, where it is shown that impossible worlds structures using binary epistemic accessibility relations are equivalent to structures using Montague-Scott neighborhood semantics.