For whatever reason, pomdp has been co-opted by the AI community, so the books are pretty lousy and show-offy, often using nonstandard terms and newfangled jargon to explain what is really plain old probability theory with some state space transitions.Thrun's Probabilistic Robotics is the best one I could find. Any math professor can run circles around the material if it were treated as part of math instead of bringing AI into the mix.