LIRa session: Alexandru Baltag

[ A recording of this talk is available here. ]

Speaker: Alexandru Baltag

Date and Time: Thursday, February 27th 2020, 16:30-18:00

Venue: ILLC Seminar Room F1.15, Science Park 107.

Title:  Tell Us All You Know


I analyze the notion of “epistemic superiority” between agents or groups (e.g. “She knows all they know”), by adding epistemic comparison statements to standard epistemic logic. I show the connection of this notion with the logic of local dependence between variables (as axiomatized in my joint paper¬† with van Benthem, recently presented at LIRa). On the dynamic side, I introduce actions by which epistemic superiority can be acquired: “sharing all one knows” (by e.g. giving access to one’s information database to all or some of the other agents), or “reading a knowledge base” (i.e. gaining such access to another’s information database, regardless of whether or not gave permission). I show that distributed knowledge is necessary to `pre-encode’ what happens to individual knowledge after such actions. As for dealing with common knowledge after these actions, we need to introduce a further generalization: the concept of “common distributed knowledge” (described for the first time in my student’s Suzanne van Wijk’s MoL thesis). I give an axiomatization of the logic of epistemic comparisons and common distributed knowledge, and I use it as a static base to axiomatize the dynamic logic of public and semi-public sharing/reading events. I move on to more complex such events involving privacy (e.g. hacking), and use an analogue of event models to describe and axiomatize them. I end with some related open questions. This is joint work with Sonja Smets.