图书介绍：Books are individual and idiosyncratic. In trying to understand what makes a good book， there is a limited amount that one can learn from other books; but at least one can read their prefaces， in hope of help. Our own research shows that authors use prefaces for many different reasons. Prefaces can be explanations of the role and the contents of the book， as in Chung [49] or Revuz [223] or Nummelin [202]; this can be combined with what is almost an apology for bothering the reader， as in BiUings