Logics have, for many years, laid claim to providing a formal basis for the study and development of applications and systems in arti?cial intelligence. With the depth and maturity of formalisms, methodologies and logic-based systems - day, this claim is stronger than ever. The European Conference on Logics in Arti?cial Intelligence (or Journ ees Europ eennes sur la Logique en Intelligence Arti?cielle, JELIA) began back in 1988, as a workshop, in response to the need for a European forum for the discussion of emerging work in this ?eld. Since then, JELIA has been organized biennially, with English as its o?cial language, previous meetings taking place in Rosco?, France (1988), Amsterdam, Nether- lands (1990), Berlin, Germany (1992), York, UK (1994), Evora, Portugal (1996), Dagstuhl,Germany(1998),M alaga,Spain(2000)andCosenza,Italy(2002). The increasinginterestinthisforum,itsinternationallevelwithgrowingparticipation from researchers outside Europe, and the overall technical quality have turned JELIA into a major biennial forum for the discussion of logic-based approaches to arti?cial intelligence. The 9th European Conference on Logics in AI, JELIA 2004, took place in Lisbon, Portugal, between the 27th and the 30th of September 2004, and was hosted by the Universidade Nova de Lisboa. Its technical program comprised 3 invited talks, by Francesca Rossi, Franz Baader, and Bernhard Nebel, and the presentationof52refereedtechnicalarticlesselectedbytheProgramCommittee among the 144 that were submitted, a number which in our opinion clearly indicates that the research area of logics in AI is one with a great and increasing interest.

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Inhalt
Invited Talks.- Representing and Reasoning with Preferences.- Engineering of Logics for the Content-Based Representation of Information.- Formal Methods in Robotics.- Multi-agent Systems.- Games for Cognitive Agents.- Knowledge-Theoretic Properties of Strategic Voting.- The CIFF Proof Procedure for Abductive Logic Programming with Constraints.- Hierarchical Decision Making by Autonomous Agents.- Verifying Communicating Agents by Model Checking in a Temporal Action Logic.- Qualitative Action Theory.- Practical Reasoning for Uncertain Agents.- Modelling Communicating Agents in Timed Reasoning Logics.- Logic Programming and Nonmonotonic Reasoning.- On the Relation Between ID-Logic and Answer Set Programming.- An Implementation of Statistical Default Logic.- Capturing Parallel Circumscription with Disjunctive Logic Programs.- Towards a First Order Equilibrium Logic for Nonmonotonic Reasoning.- Characterizations for Relativized Notions of Equivalence in Answer Set Programming.- Equivalence of Logic Programs Under Updates.- Cardinality Constraint Programs.- Recursive Aggregates in Disjunctive Logic Programs: Semantics and Complexity.- Reasoning Under Uncertainty.- A Logic for Reasoning About Coherent Conditional Probability: A Modal Fuzzy Logic Approach.- A Logic with Conditional Probabilities.- Reasoning About Quantum Systems.- Sorted Multi-adjoint Logic Programs: Termination Results and Applications.- Logic Programming.- The Modal Logic Programming System MProlog.- Soundness and Completeness of an Efficient Negation for Prolog.- Logic Programs with Functions and Default Values.- Actions and Causation.- Parallel Encodings of Classical Planning as Satisfiability.- Relational Markov Games.- On the Logic of 'Being Motivated to Achieve ?, Before ?'.- ComplexityIssues.- Representation and Complexity in Boolean Games.- Complexity in Value-Based Argument Systems.- A Polynomial Translation from the Two-Variable Guarded Fragment with Number Restrictions to the Guarded Fragment.- Description Logics.- Transforming Fuzzy Description Logics into Classical Description Logics.- Computing the Least Common Subsumer w.r.t. a Background Terminology.- Explaining Subsumption by Optimal Interpolation.- Belief Revision.- Two Approaches to Merging Knowledge Bases.- An Algebraic Approach to Belief Contraction and Nonmonotonic Entailment.- Logical Connectives for Nonmonotonicity: A Choice Function-Based Approach.- On Sceptical Versus Credulous Acceptance for Abstract Argument Systems.- Modal, Spacial, and Temporal Logics.- Line-Based Affine Reasoning in Euclidean Plane.- Measure Logics for Spatial Reasoning.- Only Knowing with Confidence Levels: Reductions and Complexity.- Time Granularities and Ultimately Periodic Automata.- Theorem Proving.- Polynomial Approximations of Full Propositional Logic via Limited Bivalence.- Some Techniques for Branch-Saturation in Free-Variable Tableaux.- Semantic Knowledge Partitioning.- Negative Hyper-resolution as Procedural Semantics of Disjunctive Logic Programs.- Applications.- Discovering Anomalies in Evidential Knowledge by Logic Programming.- Logic Programming Infrastructure for Inferences on FrameNet.- An Answer Set Programming Encoding of Prioritized Removed Sets Revision: Application to GIS.- Automatic Compilation of Protocol Insecurity Problems into Logic Programming.- Exploiting Functional Dependencies in Declarative Problem Specifications.- Combining Decision Procedures for Sorted Theories.- Meta-level Verification of the Quality of Medical Guidelines Using Interactive Theorem Proving.- Towards a Logical Analysis of Biochemical Pathways.- Systems Session.- Abductive Logic Programming with CIFF: System Description.- The DALI Logic Programming Agent-Oriented Language.- Qsmodels: ASP Planning in Interactive Gaming Environment.- A System with Template Answer Set Programs.- New DLV Features for Data Integration.- Profiling Answer Set Programming: The Visualization Component of the noMoRe System.- The PLP System.- The MyYapDB Deductive Database System.- InterProlog: Towards a Declarative Embedding of Logic Programming in Java.- IndLog Induction in Logic.- OLEX A Reasoning-Based Text Classifier.- Verdi: An Automated Tool for Web Sites Verification.- SATMC: A SAT-Based Model Checker for Security Protocols.- tabeql: A Tableau Based Suite for Equilibrium Logic.- tascpl: TAS Solver for Classical Propositional Logic.