Book Acknowledgements
Some colleagues have read and commented on parts of the book. So it is a great pleasure to thank Federico Corberi, Joachim Krug and Alessandro Sarracino. Discussions with many colleagues helped us to clarify several questions. We are especially grateful to Franco Bagnoli, Filippo Colomo, Peter Grassberger and Ruggero Vaia. Filippo Cherubini is acknowledged for having produced many figures of the book. PP thanks the Alexander von Humboldt Foundation for financial support, allowing him to spend a month at the Institute for Theoretical Physics of the University of Cologne to work on the present edition of this book.