The purpose of this paper is to study the fundamental mechanism humans use in argumentation and its role in different major approaches to commonsense reasoning in AI and logic programming. We present three novel results: We develop a theory for argumentation in which the acceptability of arguments is precisely defined. We show that logic programming and nonmonotonic reasoning in AI are different forms of argumentation. We show that argumentation can be viewed as a special form of logic programming with negation as failure. This result introduces a general method for generating metainterpreters for argumentation systems. 1.

this paper is devoted to an analysis of a specific problem area, which is not only of interest descriptively, but which also presents an interesting theoretical challenge. The descriptive area is that of the interaction between indefinites, pronouns, and epistemic modalities, a subject renowned for the many puzzles it creates, including questions concerning identity of individuals, specificity of reference, and rigidity of names. Obviously, not all of these long-standing problems can be studied in depth within the span of a single paper. The aim is merely to show that the dynamic perspective suggests interesting new solutions to some of them. The paper provides a dynamic semantics for a language of first order modal predicate logic. This system is meant to combine the dynamic semantics for predicate logic developed in Groenendijk and Stokhof 1991 with the update semantics for modal expressions of Veltman to appear. This combination is not a straightforward fusion of two distinct systems, but poses some interesting technical problems. Various people have studied this issue (see van Eijck and Cepparello to appear; Dekker 1992), and the present paper builds on their work. It tries to solve the problems in a different way, by slightly adapting the original definition of existential quantification in dynamic predicate logic, and making use of the notion of a referent system, originally developed in Vermeulen to appear b. Natural language is not the primary target of the analyses provided below. However, it is a main source of inspiration, and the paper claims that the dynamic approach which is exemplified here using a logical language, can be applied fruitfully to natural language, too. The long term aim is to come up with a logical system which may function as a tool in the...

We present a computational theory of the paragraph. Within it we formally define coherence, give semantics to the adversative conjunction "but " and to the Gricean maxim of quantity, and present some new methods for anaphora resolution. The theory precisely characterizes the relationship between the content of the paragraph and background knowledge needed for its understanding. This is achieved by introducing a new type of logical theory consisting of an object level, corresponding to the content of the paragraph, a referential level, which is a new logical level encoding background knowledge, and a metalevel containing constraints on models of discourse (e.g. a formal version of Gricean maxims). We propose also specific mechanisms of interaction between these levels, resembling both classical provability and abduction. Paragraphs are then represented by a class of structures called p-models. 1.

This thesis describes a system capable of modelling agents engaged in planning and plan recognition in a world containing multiple independent agents. It uses a database of formulae representing propositions about its domain, and a reason maintenance system to represent interdependencies between them. The system has been developed from recent ideas in domain-independent single-agent planners, but the planning process is controlled by rules that form a model of rational thought. Agents are modelled as having beliefs and goals, reasoning, acting and perceiving actions. They reason about each other's reasoning using the same model of rationality as the system uses to model them.

We analyze IF/hyper-classical games by bringing together two viewpoints from Jaakko Hintikka's work: game semantics, and epistemic logic. In the process, we link up between logic and game theory.

Dynamic logic, broadly conceived, is the logic that analyses change by decomposing actions into their basic building blocks and by describing the results of performing actions in given states of the world. The actions studied by dynamic logic can be of various kinds: actions on the memory state of a computer, actions of a moving robot in a closed world, interactions between cognitive agents performing given communication protocols, actions that change the common ground between speaker and hearer in a conversation, actions that change the contextually available referents in a conversation, and so on. In each of these application areas, dynamic logics can be used to model the states involved and the transitions that occur between them. Dynamic logic is a tool for both state description and action description. Formulae describe states, while actions or programs express state change. The levels of state descriptions and transition characterisations are connected by suitable operations that allow reasoning about pre- and postconditions of particular changes.

Proof animation is a way of executing proofs to find errors in the formalization of proofs. It is intended to be "testing in proof engineering". Although the realizability interpretation as well as the functional interpretation based on limit-computations were introduced as means for proof animation, they were unrealistic as an architectural basis for actual proof animation tools. We have found game theoretical semantics corresponding to these interpretations, which is likely to be the right architectural basis for proof animation.

We develop a variant of Least Fixed Point logic based on First Order logic with a relaxed version of guarded quantification. We develop a Game Theoretic Semantics of this logic, and find that under reasonable conditions, guarding quantification does not reduce the expressibility of Least Fixed Point logic. But guarding quantification increases worst-case time complexity.

Abstract. The study of multi-agent systems is proving to be an exciting and active research field within computer science. Communication is an important aspect of multi-agent systems, and the protocols that are used to provide a shared definition of what agents can say to each other, along with the meaning of what agents say, receive much attention from researchers. At present, there are a number of well-defined protocols, agent communication languages, and protocol specification languages available, yet, there is no formal mathematical theory of agent interaction protocols. The authors believe that such a theory would be beneficial to the field of agent communication and multi-agent systems in general. In this paper, we present an application of the mature field

As a language for exchanging computer-"understandable" representations of mathematical formulas and concepts, OpenMath has a fairly standard syntactic structure for most