I dedicate this book to my wife Sigrid and to my ten-year-old son Wolfgang, who helped me to write the computer program producing Fig. 7.1.

• 谨以此书献给我的妻子西格丽德，和我十岁的儿子沃尔夫冈，他帮助我写了描绘插图7.；1的计算机程序。