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SCOPE OF THE SERIESLogic is applied in an increasingly wide variety of disciplines, from the traditional subjects of philosophy and mathematics to the more recent disciplines of cognitive science, computer science, artificial intelligence, and linguistics, leading to new vigor in this ancient subject. Springer, through its Applied Logic Series, seeks to provide a home for outstanding books and research monographs in applied logic, and in doing so demonstrates the underlying unity and applicability of logic.

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Abstract. We extend the Description Logic ALC with a "typicality" operator T that allows us to reason about the prototypical properties and inheritance with exceptions. The resulting logic is called ALC + T. The typicality operator is intended to select the "most normal" or "most typical" instances of a concept. In our framework, knowledge bases may then contain, in addition to ordinary ABoxes and TBoxes, subsumption relations of the form "T(C) is subsumed by P ", expressing that typical C-members have the property P . The semantics of a typicality operator is defined by a set of postulates that are strongly related to KrausLehmann-Magidor axioms of preferential logic P. We first show that T enjoys a simple semantics provided by ordinary structures equipped by a preference relation. This allows us to obtain a modal interpretation of the typicality operator. Using such a modal interpretation, we present a tableau calculus for deciding satisfiability of ALC + T knowledge bases. Our calculus gives a nondeterministic-exponential time decision procedure for satisfiability of ALC + T. We then extend ALC + T knowledge bases by a nonmonotonic completion that allows inferring defeasible properties of specific concept instances 1 .

We present two embeddings of Lukasiewicz logic L into Meyer and Slaney's Abelian logic A, the logic of lattice-ordered Abelian groups. We give new analytic proof systems for A and use the embeddings to derive corresponding systems for L. These include hypersequent calculi, terminating hypersequent calculi, co-NP labeled sequent calculi, and unlabeled sequent calculi.

A uniform proof-theoretic reconstruction of the major nonmonotonic logics is introduced. It consists of analytic sequent calculi where the details of nonmonotonic assumption making are modelled by an axiomatic rejection method. Another distinctive feature of the calculi is the use of provability constraints that make reasoning largely independent of any specific derivation strategy. The resulting account of nonmonotonic inference is simple and flexible enough to be a promising playground for investigating and comparing proof strategies, and for describing the behavior of automated reasoning systems. We provide some preliminary evidence for this claim by introducing optimized calculi, and by simulating an existing tableaux-based method for circumscription. The calculi for skeptical reasoning support concise proofs that may depend on a strict subset of the given theory. This is a difficult task, given the nonmonotonic behavior of the logics.

In this paper we present a cut-free sequent calculus, called SeqS, for some standard conditional logics. The calculus uses labels and transition formulas and can be used to prove decidability and space complexity bounds for the respective logics. We also show that these calculi can be the base for uniform proof systems. Moreover, we present CondLean, a theorem prover in Prolog for these calculi. ACM Reference Format:Olivetti, N., Pozzato, G., and Schwind, C., 2007. A sequent calculus and a theorem prover for standard conditional logics. ACM Trans. Comput.Article 22 / 2 • N. Olivetti et al.

We extend the Description Logic ALC with a "typicality" operator T that allows us to reason about the prototypical properties and inheritance with exceptions. The resulting logic is called ALC + T. The typicality operator is intended to select the "most normal" or "most typical" instances of a concept. In our framework, knowledge bases may then contain, in addition to ordinary ABoxes and TBoxes, subsumption relations of the form "T(C) is subsumed by P ", expressing that typical C-members have the property P . The semantics of a typicality operator is defined by a set of postulates that are strongly related to Kraus-Lehmann-Magidor axioms of preferential logic P. We first show that T enjoys a simple semantics provided by ordinary structures equipped with a preference relation. This allows us to obtain a modal interpretation of the typicality operator. We show that the satisfiability of an ALC+T knowledge base is decidable and it is precisely EXPTIME. We then present a tableau calculus for deciding satisfiability of ALC + T knowledge bases. Our calculus gives a (suboptimal) nondeterministic-exponential time decision procedure for ALC + T. We finally discuss how to extend ALC + T in order to infer defeasible properties of (explicit or implicit) individuals. We propose two alternatives: (i) a nonmonotonic completion of a knowledge base; (ii) a "minimal model" semantics for ALC + T whose intuition is that minimal models are those that maximise typical instances of concepts.