The Schedule

Common Distributed Knowledge and the Majority Agreement task

Jérémy Ledent

Tool-Supported Action Model Synthesis for Truly Private Model Updates

Thomas Schlögl

How groups communicate - variations in (a)synchronicity and models

Clara Lerouvillois and Hans van Ditmarsch

Hypergraph Semantics for Modal Logics: Axiomatizations and Limitations

Valentin Müller

Implementability of Concurrent Objects from a Topological Perspective

Armando Castañeda

A guided tour of probabilistic dynamic epistemic logic

Barteld Kooi

Asynchronous DEL for Pure Exchange Events

Alexandru Baltag

 Lunch  - (outside room 3052)

Declarative specification of distributed algorithms: shorter, faster, higher-level

Murdoch James Gabbay

I will outline ideas on how to compactly represent distributed algorithms as axiomatic theories in three-valued logic.  The talk will be based on the following papers: 1. "Declarative distributed algorithms as axiomatic theories in three-valued modal logic over semitopologies" https://arxiv.org/abs/2512.21137 (in press with the Journal of Applied Logics) 2. "A declarative approach to specifying distributed algorithms using three-valued modal logic" https://arxiv.org/abs/2502.00892 (submitted)

Direct FMP for Distributed Knowledge and its Extensions

Alexandru Baltag

The usual proof of completeness and decidability for the logic of Distributed Knowledge and its extensions proceeds in two steps: 

(1) construct a finite (Kripke) pseudo-model (by modal filtration: essentially, a quotient of the canonical pseudo-model) in which group relations do NOT satisfy the Intersection Property;  (2) unravel this into an infinite tree-model, and redefine the epistemic relations to make it into a standard model. 

However, this method does NOT prove that the logic has Finite Model Property. To do this, people usually appeal to higher-level Combinatorial results, or techniques from Automata Theory.

In this talk, I present a direct and intuitive proof of FMP (and completeness ) for the logic of Distributed Knowledge and its extensions (including Common Distributed Knowledge and other fixed-point modalities). I show how the proof can be best understood when stated in terms of local states (vertices of a simplicial complex). Essentially. it provides a Representation Theorem for finite (Kripke) pseudo-models as a p-morphic image of a finite simplicial complex.