At the end of all the work needed for the publication of this book, I owe my thanks to all those who helped me revisit my ideas and improve their presentation: Claude Amar, Jean-Marc Bret, Alain Roy, Patrick van Leynseele and Adeline Guilhen.

My wife, Leslie Lemons, deserves special thanks for having accepted the invasion of most of our free time the past four years while working on this project as well as accepting to proofread the English version. Moreover she kept encouraging me and even showed enthusiasm when reading it. I wish everyone who undertakes to write a book would receive such wonderful support.