Logics for Information Update a tutor ia l for TARK Siena 2001

This tutorial presents an overview of update logics for communicative actions. The basic tool is: Hintikka-Kripke models for epistemic languages. The difficult questions axe twofold. First, what precise updates axe induced by various types of communicative action? One line in the literature has looked at examples of increasing complexity. Models and update procedures are simple for questions/answers, or public announcements, but they get much more complex as communication gets more 'private'. We follow one such line in current research, referring to work by Veltman, Groeneveld & Gerbrandy, and Baltag, Solecki & Moss on information update in conversation and games, whose current challenges include more complex linguistic expressions, defaults and cryptographic communication. This requires building sophisticated models in harmony with the observed phenomena. Our second topic concerns new logical issues in this setting. In a way, all relevant dynamics is contained in existing epistemic logics cure temporal models. But this observation is no more useful than saying we can do most of modern logic inside first-order logic, and all of it inside set theory. Instead, we survey new questions beyond the usual agenda. Examples are: (a) relating model-theoretic to syntactic views of update, (b) (non-)persistence of assertions under update, (c) calculi for short-term dynamic 'local inference', and connections with longer-term 'global inference'.