Available now online:
PhD Thesis: Reasoning about Time, Action and Knowledge in Multi-Agent Systems

This is a joint work with H. P. VAN DITMARSCH and R. VERBRUGGE.
PDF Download: Sum and Product in Dynamic Epistemic Logic
Abstract:
The Sum-and-Product riddle was first published in the reference H. Freudenthal (1969, Nieuw Archief voor Wiskunde 3, 152) [6].We provide an overview on the history of the dissemination of this riddle through the academic and [...]

This is a joint work with Professor Jan van Eijck(CWI, Netherlands), and Tomasz Sadzik(Stanford, USA). It was presented in Games, action and social software Workshop , 30 Oct – 3 Nov 2006 @ Lorentz Center, Leiden, the Netherlands.
A pre-publication version is open for download: Action Emulation.
Abstract:
The effects of public announcements, private communications, deceptive messages [...]

Authors: H.P. van Ditmarsch, J. Ruan, and W. van der Hoek
Abstract: We give a relation between a logic of knowledge and change, with a semantics on Kripke models, and a logic of knowledge and time, with a semantics on interpreted systems. More in particular, given an epistemic state (pointed multi-agent Kripke model where all accessibility [...]

Authors: Hans van Ditmarsch and Ji Ruan
Résumé :
Dans les puzzles épistémiques les annonces d’ignorance, ou des séquences de tels annonces, souvent résultent en connaissances. Nous présentons le puzzle ‘Quelle Somme ?’, et le modèlisent dans la logique des annonces publiques – un langage logique avec des opérateurs dynamiques et épistémiques. La solution du puzzle [...]

Authors: H. van Ditmarsch, J. Ruan, and L.C. Verbrugge
Abstract: We model the well-known Sum-and-Product problem in a modal logic, and verify its solution in a model checker. The modal logic is public announcement logic. The riddle is then implemented and its solution verified in the epistemic model checker DEMO.
Download: this paper in pdf.
BibTex (from DBLP):
@inproceedings{DBLP:conf/ausai/DitmarschRV05,
[...]