ABSTRACT
The reader is just opening this book, slowly reading the first lines a~ld starting to build up an impression of what may be contained in the following pages. How can we give this reader an idea of the book's importance for us, and what has driven us to devote energy to writing it over a long period of time (which we could easily have spent on easier jobs)? These are the wistful thoughts of many authors sitting in front of a manuscript which has achieved a certain status - or at least size - through being written, rewritten and finally polished. It is now to be given the last finishing touch: the introduction, which will introduce some key ideas and whet the reader's appetite to read on.
