Raymond Smullyan and Logic

I am posting now on Raymond Smullyan, who most of you have probably never heard of.  However, in my opinion, he is one of the most brilliant people in our age.  He is 88-89, and is a logician.   He has written numerous books, all using recreational logic in puzzles.  Many of his puzzles involve Knights, who always tell the truth, and Knaves, who always lie.  Each will make a statement about the other, or the other's statement, or both, which allows you to figure out who's a Knight, and who's a Knave.  He is famous for having created "The hardest logic puzzle ever".  In the land in which it is set, there are humans and vampires.  Sane humans and insane vampires always tell the truth, while insane humans and sane vampires always lie.  In addition, each uses a word ("da" or "bal") for yes or no, but you don't know which is which.  You need to figure out which is yes and which is no, and whether the speaker is a sane or insane human, or a sane or insane vampire.  I highly enjoy his books (even though I never solved the hardest logic puzzle ever) and hope you will look in your library system for some of them as well.