Prof. Olivier Danvy is editor in chief of the Higher Order for Symbolic Computation journal, and is also editor for two books in the LNCS series. This book is written for Dr. Robert (Bob) Paige. Bob Paige, a professor of computer science and a leading researcher in the area of programming languages and transformational programming. Dr. Paige was the author of many research papers, covering related topics in programming languages, compilers, algorithms, and database design. An invited speaker at conferences and university seminars around the world, he also served regularly as a reviewer of research projects for major government agencies. He was a devoted mentor of PhD students who today hold research positions at leading universities and research centers.