I have particularly benefited from the encouragement, suggestions, and adept criticisms of Dr. Bruno S. Frey, Professor at the Institute of Empirical Economic Studies at the University of Zurich, and his colleagues.

• 苏黎世大学实证经济研究所教授布鲁诺·S·弗雷博士和他的同事给予我的鼓励、建议和深刻的批评使我受益匪浅。