Zhang Yu, a famous teacher, Dr. Ai Qihang, a national expert in mathematics counseling for postgraduate entrance examination, a backbone teacher in the construction of national excellent courses of the Ministry of Education, the author of the national best-selling Lecture on Advanced Mathematics 18 and the classic on the origin of postgraduate entrance examination mathematics 1000, and one of the editors of the national unified examination reference book (outline analysis) of higher education press.

Zhang Yu has the titles of "Yu Ge" and "Shen Yu" among the students who take the postgraduate entrance examination, and has a humorous personality. "Give up the postgraduate entrance examination immediately" is a sentence he often involves when talking about some difficult problems in his lectures. Many students are already a little annoyed when they hear the problem. Brother Yu's sentence is both funny and can rekindle students' interest.