Logics for Epistemic Actions: Completeness, Decidability, Expressivity
Abstract
We consider dynamic versions of epistemic logic as formulated in Baltag and Moss "Logics for epistemic programs" (2004). That paper proposed a logical language (actually families of languages parameterized by action signatures) for dynamic epistemic logic. It had been shown that validity in the language is Pi-1-1-complete, so there are no recursively axiomatized complete logical systems for it. In contrast, this paper proves a weak completeness result for the fragment without action iteration, and a strong completeness result for the fragment without action iteration and common knowledge. Our work involves a detour into term rewriting theory. The argument uses modal filtration, and thus we obtain the finite model property and hence decidability. We also give a translation of our largest language into PDL, thereby obtaining a second proof of decidability. The paper closes with some results on expressive power. These are mostly concerned with comparing the action-iteration-free language with modal logic augmented by transitive closure operators. We answer a natural question about the languages we obtain by varying the action signature: we prove that a logical language with operators for private announcements is more expressive than one for public announcements.
Cite
@article{arxiv.2203.06744,
title = {Logics for Epistemic Actions: Completeness, Decidability, Expressivity},
author = {Alexandru Baltag and Lawrence S. Moss and Slawomir Solecki},
journal= {arXiv preprint arXiv:2203.06744},
year = {2022}
}
Comments
This paper was intended to be the "journal" version of our 1998 paper "The logic of common knowledge, public announcements,and private suspicions." It was mainly written in 2004, with a few bibliographic additions coming a few years later