Acknowledgments We are very grateful to all our students and colleagues who contributed to the cre- ons and useful com Sariel Har-Peled,Johan Hastad,Rani Hod,Mihyun Kang,Michael Krivelevich, Eyal Lubetzky,Russell Lyons,Nabil Mustafa,Nathan Linial,Yuval Peres,Xue Rui, Alexander Sapozhenko,Asaf Shapira,Aravind Srinivasan,Benny Sudakov,Prasad Tetali and William Wu,who pointed out various inaccuracies and misprints,and suggested improvements in the presentation as well as in the results.Needless to say,the responsibility for the remaining mistakes,as well as the responsibility for It is a pleasure to tha help in the preparation of the final manuscript for this book.Acknowledgments We are very grateful to all our students and colleagues who contributed to the cre￾ation of this third edition by joint research, helpful discussions and useful com￾ments. These include Miklos Bona, Andrzej Dudek, Mathieu Dutour, Juliana Freiré, Sariel Har-Peled, Johan Hastad, Rani Hod, Mihyun Kang, Michael Krivelevich, Eyal Lubetzky, Russell Lyons, Nabil Mustafa, Nathan Linial, Yuval Peres, Xue Rui, Alexander Sapozhenko, Asaf Shapira, Aravind Srinivasan, Benny Sudakov, Prasad Tetali and William Wu, who pointed out various inaccuracies and misprints, and suggested improvements in the presentation as well as in the results. Needless to say, the responsibility for the remaining mistakes, as well as the responsibility for the (hopefully not many) new ones, is solely ours. It is a pleasure to thank Rani Hod and Eyal Lubetzky for their great technical help in the preparation of the final manuscript for this book. xv