The so-called worldwide mathematical problems are generally difficult to solve in the exponential field, and the Department of Mathematics of Tsinghua University of Peking University is naturally included in the "Department of World Mathematics". In fact, if we only talk about mathematics, there are many universities in the world that are better than Peking University and Tsinghua. Imagine that even so many mathematicians in Princeton and Stanford University can't solve problems, and doctors in the Department of Mathematics of Tsinghua University in Peking University can't overcome them. What's so strange about it?