Mr Chongyi Yuan retired as a professor from School of Information Science, Peking University 2005. He worked for more than 28 years, at Institute of Mathematics, Chinese Academy of Sciences since his graduation from the Department of Mathematics, Nanjing University in 1964. He was transferred to the Department of Computer Science, Peking University in 1993, where he taught two master courses based on his research interests: Petri nets and formal semantics. As a visiting scholar, he spent more than 2 years at Toronto University and Waterloo University, Canada; and more than 3 years at GMD, Bonn (west) Germany. Prof. Chongyi Yuan has published four books on Petri nets in Chinese and one book on theory of programming in English.