Exploring the iterated update universe
Tomasz Sadzik

Abstract:
We investigate the asymptotic properties of the logical system for
information update developped by Baltag, Moss and Soleck. We build on
the idea of looking at update logics as dynamical systems. We show
that every epistemic formula either always holds or is always refuted
from certain moment on, in the course of update with factual epistemic
events, i.e. events with only propositional prerequisite formulas, or
signals. We characterize in terms of a pebble game the class of frames
such that iterated update with factual epistemic events built over
them gives rise only to finite sets of reachable states. The
characterization is nontrivial, and so the 'Finite Evolution
Conjecture' is refuted.  Finally, after giving some basic insights
into the dissipative nature of update with general, nonfactual
epistemic events, we show the distinctive stabilizing nature of
epistemically ordered multi-S5 events - events in which agents can be
ordered in terms of how much they know.