Automated reasoning about actions

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Lee, Joohyung

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The study of reasoning about a tions is an important subarea of the theory of ommonsense reasoning. It is on erned with developing appropriate systems of logi for des ribing a tions and their e e ts on the world. In spite of the fa t that this reasoning is based on ommon sense and does not involve any spe ialized knowledge, attempts to formalize it using lassi al logi en ountered serious diÆ ulties, whi h have led to the emergen e of a new eld, nonmonotoni logi s. In parti ular, M Cain and Turner introdu ed the ausal logi in whi h the notions of \being aused" and \being true" are distinguished. Based on their logi , Giun higlia and Lifs hitz proposed a high level a tion language C, whi h is a formal model of parts of natural language that are used for des ribing properties of a tions. The ausal logi and C, along with the on ept of satis ability planning, provided us with a widely appli able and eÆ ient method of automated reasoning about a tions, whi h led to the reation of the Causal Cal ulator (CCal ). vii In this dissertation, we have identi ed several essential limitations of the M Cain{Turner ausal logi and a tion language C. To over ome these limitations, we de ned an extension of the ausal logi to multi-valued formulas and a new a tion language C+. Language C+ an represent non-propositional uents, de ned

uents, additive uents, rigid onstants, and defeasible ausal laws. Se ond, we have redesigned and reimplemented CCal to a

ount for these extensions, and tested the new CCal and the underlying theory by applying them to several new, more diÆ ult examples of ommonsense reasoning. The input language of the new CCal is more elaboration tolerant than the old version. Last, we have shown how to turn ausal logi into propositional logi based on the idea of \loop formulas" that originated from logi programming under the answer set semanti s.