Multi-agent dynamic-epistemic logic
Johan van Benthem · Cambridge University Press eBooks · 2011
The public announcements or observations !P studied in Chapter 3 are an easily described way of conveying information. The only difficulty may be finding good static epistemic models for the initial situation where updates start. But information flow gets much more challenging once we give up the uniformity in this scenario. In conversation, in games, or at work, agents need not have the same access to the events currently taking place. When I take a new card from the stack in our current game, I see which one I get, but you do not. When I overhear what you are telling your friend, you may not know that I am getting that information. At the website of your bank, you have an encrypted private conversation which as few people as possible should learn about. The most enjoyable games are all about different information for different players, and so on. In all these cases, the dynamics itself poses a challenge, and elimination of worlds is definitely not the right mechanism. This chapter is about a significant extension of PAL that can deal with partially private information, reflecting different observational access of agents to the event taking place. We will present motivating examples, develop the system DEL , and explore some of its technical properties. As usual, the chapter ends with a number of further directions and open problems, from practical and philosophical to more mathematical. DEL is the true paradigm of dynamic-epistemic logic, and its ideas will return over and over again in this book.