Autumn Semester HS2026

Unless stated otherwise, all talks will take place in room ExWi 228 of the Exakte Wissenschaft Building (ExWi) at the University of Bern.

Schedule

Abstracts

A well-studied phenomenon in network theory since the 1970s are optimal schedules to distribute information by one-to-one communication between nodes that are connected in the network. One can take these communicative actions to be telephone calls, and protocols to spread information this way are known as gossip protocols or epidemic protocols. A common abstraction is to call the information of each agent its secret, and that the goal of information dissemination is that all agents know all secrets: that is the termination condition of gossip protocols. Following investigations assuming a global scheduler, it is now typically assumed that gossip protocols are distributed in some way, where the only role of the environment is to ensure randomization. Statistical approaches to gossip have taken a large flight since then, wherein network topology is an important parameter.
In epistemic gossip protocols, an agent (node) will call another agent not because it is so instructed by a scheduler, or at random, but based on its knowledge or ignorance of the distribution of secrets over the network and of other agents’ knowledge or ignorance of that. One such protocol requires that an agent may only call another agent if it does not know the other agent’s secret. Epistemic features of gossip protocols may affect their termination, the (order of complexity) expectation of termination, their reachability (what distributions of secrets may occur before all agents know all secrets), and so on. Variations involve agents exchanging telephone numbers in addition to agents exchanging secrets (which results in network expansion), agents exchanging knowledge about secrets, common knowledge of the protocol, agents communicating by full information protocols, and gossip protocols with errors and error correction. We present a survey of distributed epistemic gossip protocols.
'Reasoning about Gossip' is also the title of a textbook that will appear January 2027 as volume 64 of Cambridge Tracts in Theoretical Computer Science published by Cambridge University Press. A website for the book is reasoningaboutgossip.eu.

BIO
Hans van Ditmarsch is emeritus senior researcher (directeur de recherche) at CNRS in France, and visiting professor at IIT (Indian Institute for Technology) Kanpur in India. He lives in the Netherlands. He is visiting Thomas Studer's group at University Bern in the months of September and October 2026.