{"type":"ScholarlyArticle","title":"Inaccessible Worlds and Irrelevance: Preliminary Report","authors":[{"name":"Craig Boutilier","slug":"craig-boutilier","given":"Craig","family":"Boutilier","affiliation":""}],"abstract":"Recently, the relationship between several forms of default reasoning based on conditional defaults has been investigated. In particular, the systems based on £-semantics, preferential models, and (fragments of) modally-defined, conditional logics have been shown to be equivalent. These systems form a plausible core for default inference, but are too weak in general, failing to deal adequately with irrelevance. We propOse an extension of the (modal) conditional logics in which one can express the truth of sentences at inaccessible possible worlds and show how this logic can be used to axiomatize a simple preference relation on the modal structures of this logic. This preferential semantics is shown to be equivalent to !-entailment and rational closure. We suggest that many metalogical systems of default inference can be axiomatized within this logic, using the notion of inaccessible worlds.","doi":null,"url":"https://ijcai.org/proceedings/1991/62","pdf":"https://ijcai.org/proceedings/1991/0062.pdf","markdown":"https://ijcai.org/proceedings/1991/62.md","bibtex":"https://ijcai.org/proceedings/1991/bibtex/62","volume":{"slug":"1991","title":"Proceedings of the Twelfth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 1991","url":"https://ijcai.org/proceedings/1991/","year":1991,"location":"Sydney, New South Wales, Australia","dates":"24-30 August 1991","editors":"John Mylopoulos and Ray Reiter","isbn":"","publisher":"International Joint Conferences on Artificial Intelligence","doi_prefix":""},"section":"Knowledge Representation","track":"Knowledge Representation","number":62,"pages":{"first":413,"last":417},"keywords":[],"videos":[],"references":[],"license_note":"Copyright International Joint Conferences on Artificial Intelligence."}