In this talk I give a short introduction into theory and applications of action languages - simple logical formalisms for modeling dynamic system. A theory (action description) of an action language defines a transition diagram containing all possible trajectories of the system. Due to the size of the diagram, the problem of finding its concise specification is not trivial and has been a subject of research for a comparatively long time. Its solution requires the good understanding of the nature of causal effects of actions in the presence of complex interrelations between fluents (propositions whose truth value may depend on the state of the system). An additional level of complexity is added by the need to specify what is not changed by actions. The latter, known as the frame problem, is often reduced to the problem of finding a concise and accurate representation of the inertia axiom, a default which says that things normally stay as they are. The search for such a presentation substantially influenced AI research during the last twenty years. In this talk, I present the syntax and semantics of an action language, called AL, give the relationship between AL and the language of logic programs under the answer set/stable model semantics, and explain how this relationship can be used for building intelligent agents capable of planning, diagnostics, and other interesting types of reasoning.

Joseph Y. Halpern, Computer Science Department, Cornell UniversityItacha, NY, USA ABSTRACT Nash equilibrium is the most commonly-used notion of equilibrium in game theory. However, it suffers from numerous problems. Some are well known in the game theory community; for example, the Nash equilibrium of repeated prisoner's dilemma is neither normatively nor descriptively reasonable. However, new problems arise when considering Nash equilibrium from a computer science perspective: for example, Nash equilibrium is not robust (it does not tolerate "faulty" or "unexpected" behavior), it does not deal with coalitions, it does not take computation cost into account, and it does not deal with cases where players are not aware of all aspects of the game. In this talk, I discuss solution concepts that try to address these shortcomings of Nash equilibrium.

I concetti della filosofia appaiono spesso vaghi ed elusivi agli occhi dello scienziato. La scienza si avvale tuttavia di tecniche in cui si possono talvolta riconoscere pensieri che appartengono alle origini più remote del discorso filosofico. D’altra parte ci sono pure concetti intuitivi, nel ragionamento scientifico, che richiedono ancora di essere chiariti, e per i quali potrebbe essere utile tener conto della terminologia filosofica. Questo sembra accadere, in modo sorprendente, nella teoria matematica della calcolabilità, sia per gli aspetti teorico-fondazionali, sia per gli aspetti più applicativi pertinenti alla scienza del calcolo.