Modal logic & all that

As some of you know I recently began working on my PhD thesis. I have a lot of fun (really!) reading about new (to me) stuff such as modal logic, epistemic logic, common knowledge and μ-calculus. I already did some work in the field of logic, but this was mainly classical mathematical logic and proof theory and had only some basic knowledge in fields mentioned above. As I see now, I should have looked at them earlier, they are lots of fun for several reasons. First of all: epistemic logic has various (natural!) connections to lots of different fields: philosophy, game theory, mathematics and computer science. Second: This is the first time in my mathematical career that I'm able to explain at least some basic ideas to my non-mathematical friends (if they'd only ask...). Third: there are all this funny riddles, like the wise men puzzle (although I prefer this solution), the muddy children puzzle (which is the less violent version of what is called Josephine's puzzle in the first source to the wise men puzzle) or the mind tingling surprise test paradox.

Interested? I'll try to keep you up to date on this topic, but in the meantime I recommend the excellent book Reasoning about Knowledge by Fagin, Halpern, Moses and Vardi. For a start you might also spend some thoughts on Plato's famous tripartite definition of knowledge as justified true belief.