Guiding light: An essay for Professor Lincheng Zhao on the occasion of his 80th birthday

Lincheng Zhao was admitted to the Department of Applied Mathematics of the University of Science and Technology of China (USTC) in 1960, three years before me, and then took a year off due to illness and transferred to the entering class of 1961. We were both not good at socializing, so although we had been classmates for three years, we didn’t know each other. In 1978, when we were both admitted to the Department of Mathematics for graduate studies, we got to know each other. Since then, we have known each other, made friends, and helped each other in all aspects of research and life, and we have become good mentors and friends with each other. On the occasion of Professor Zhao’s 80th birthday, I would like to recall a little of the past events of our acquaintance and friendship to express my gratitude to Academic Elder Brother Zhao.