We are happy to announce that the LUCI Lab seminar series 2026 will host
Thomas Ågotnes
(University of Bergen) via Teams on Wednesday
March 11th
, starting from
2:30
pm CET.
- Title
Anonymous Public Announcements
Joint work with Rustam Galimullin, Ken Satoh, and Satoshi Tojo.
Abstract:
We formalise the notion of an anonymous public announcement in the tradition of public announcement logic. Such announcements can be seen as in-between a public announcement from “the outside” (an announcement of phi) and a public announcement by one of the agents (an announcement of K_a phi): we get more information than just phi, but not (necessarily) about exactly who made it.
Even if such an announcement is prima facie anonymous, depending on the background knowledge of the agents it might reveal the identity of the announcer: if I post something on a message board, the information might reveal who I am even if I don’t sign my name. Furthermore, like in the Russian Cards puzzle, if we assume that the announcer’s intention was to stay anonymous, that in fact might reveal more information.
In this paper we first look at the case when no assumption about intentions are made, in which case the logic with an anonymous public announcement operator is reducible to epistemic logic. We then look at the case when we assume common knowledge of the intention to stay anonymous, which is both more complex and more interesting: in several ways it boils down to the notion of a “safe” announcement (again, similarly to Russian Cards).
Main results include formal expressivity results and axiomatic completeness for key logical languages.