Duan Yun originally thought that Guo Haitao would give him some strange questions, but when he got this piece of paper full of test questions, he was stunned for a moment.

There are four questions on this A4 sheet.

In Duan Yun's opinion, the first question is surprisingly simple, it is completely a college entrance examination-type math problem, and for a person like Duan Yun who is proficient in mathematics, there is no challenge at all.

The second question is also not very difficult, but when solving this question, it takes a university to get in touch with advanced mathematics knowledge, and there is no challenge to Duan Yun.

"Teacher Guo, do you have a pen?" Duan Yun asked with a smile.

"Here!" Guo Haitao handed Duan Yun a carbon pen that had already been prepared, and said with a smile: "This kind of question is not difficult for you, right?"

"It's okay. After Duan Yun took the pen, he quickly answered the first two questions almost without thinking.

This kind of topic is obviously a topic that Guo Haitao intends to test his mathematical foundation, as long as he has studied relevant university mathematical theories, he can make it.

In Duan Yun's opinion, Guo Haitao came up with these two questions just to see how far Duan Yun's mathematical foundation had reached, after all, when Duan Yun won the national championship this time, he had only just entered the first year of high school.

Sure enough, seeing that Duan Yun easily answered the first two questions, Guo Haitao's face suddenly showed a satisfied smile.

If Duan Yun had already mastered the knowledge of mathematics in college, he would indeed be able to save Guo Haitao a lot of time to cultivate.

However, when Duan Yun saw the third question, his brows suddenly furrowed slightly.

Compared with the first two questions, the difficulty of the third question has increased significantly by more than one level, and it seems to be the same Olympiad type of question, but the algorithm involved obviously requires the advanced mathematics knowledge of the university.

Even in Duan Yun's opinion, the difficulty of this question is even more difficult than any test question he has been exposed to before, even including the last most difficult question in the last National Mathematics Olympiad competition!

"Don't worry, take your time, I'll cook for you later, let's drink a little less together in the evening." Guo Haitao said with a smile on the side. 、

Seeing Duan Yun falling into contemplation at this time, this was also something Guo Haitao expected.

As Duan Yun had guessed before, the first two questions given to him by Guo Haitao were indeed only used to find out Duan Yun's mathematical foundation, and they were not much difficult in themselves.

But the third question on this piece of paper is the real test for Duan Yun.

Guo Haitao has been working part-time for the National Mathematics Olympiad all year round to formulate exam papers, and has very rich experience in propositions, but in the past, it was basically a difficult test question for junior high and high school, but this time, it is a difficult Olympiad test question for college!

This problem involves a lot of college math knowledge, including functional analysis, topology, and complex functions.

At the beginning, for this test question, Guo Haitao spent three days of spare time before finally coming up with it.

In Guo Haitao's opinion, the difficulty of this kind of problem, even if it is handed over to those students of the Department of Mathematics of Huaqing University, there should not be many solutions that can be solved, which shows how difficult this problem is!

However, what Guo Haitao didn't expect was that Duan Yun had already come up with a solution at this moment, but he still wanted to do the same as before, trying to streamline the steps of solving the problem.

Today's Duan Yun is no longer the high school student who relies on the Olympiad to win scholarships and guaranteed qualifications, he does this problem out of his love for mathematics and entertainment.

Duan Yun really chose to be proficient in mathematics just because he wanted to make money from the Olympiad competition, but when Duan Yun really became a master of mathematics, he had already begun to have a natural love for mathematics.

Just like a person who plays chess, when his level is getting higher and higher, he will become more and more enthusiastic about playing chess.

And Duan Yun was willing to meet Guo Haitao this time and accept the invitation to come to Huaqing as a guest, which was also because of his love for mathematics.

Obviously, Duan Yun has begun to use mathematics as a form of leisure.

"I'll go boil some water first, don't rush, take your time......"

After another moment, Guo Haitao saw that Duan Yun still hadn't answered the third question, and a faint disappointment flashed in his eyes, but he still smiled and encouraged Duan Yun.

Then, Guo Haitao got up and walked to the kitchen.

Duan Yun didn't know about Guo Haitao's departure at all.

After another moment, Duan Yun finally took a blank piece of paper and began to write and answer.

Guo Haitao in the kitchen seemed to be on the phone, and his tone was quite relaxed, as if he was on the phone with his family.

And during this time, Duan Yun had already solved half of this problem.

"Huh?" After half a ring, when Guo Haitao returned to the living room, he saw that Duan Yun had already written out half a piece of paper for the answer, he was stunned at first, and then walked over with a happy face.

However, when Guo Haitao saw the answer written by Duan Yun, a touch of disappointment suddenly flashed on his face again.

Guo Haitao's question involves several mathematical knowledge points that are fixed, but judging from the answers Duan Yun has written so far, it is obviously very different from the standard answer in his heart, so in Guo Haitao's opinion, this kind of answer is fundamentally wrong!

"Duan Yun, you ......" Guo Haitao sat next to Duan Yun again, and when he was about to give him a little reminder, his eyes instantly froze.

Because he suddenly found that Duan Yun's way of solving the problem was correct! And the final answer was exactly the same as Guo Haitao's setting!

What shocked Guo Haitao the most was that Duan Yun actually succeeded in shortening the solution step of his problem by two steps this time!

Although it is only two steps shortened, it requires a high level of mathematical attainment, and it is even more difficult than most people think!

"Mr. Guo, do you see that I have the right answer to this question?" At this time, Duan Yun handed the written answer to Guo Haitao and said with a smile.

"Yes, that's right!" Guo Haitao's hand holding the answer paper trembled slightly, and his face showed an unconcealable excitement.

Based on this question alone, Guo Haitao can conclude that Duan Yun's mathematics level has completely reached the level of top students in the Department of Mathematics of Huaqing University, and even higher than the level of these students.

Originally, Guo Haitao wanted to train Duan Yun for a period of time and let him learn some basic college mathematics knowledge, after all, Duan Yun was only a high school student before, and no matter how talented he was, he also needed to learn basic college knowledge.

But now it seems that there is no need to make up for the courses that have been studied!

"Duan Yun, will you come to Kyoto often in the future?" After a while, Guo Haitao suddenly asked Duan Yun.

"Yes. Duan Yun replied casually, but then focused on the fourth question.

And seeing the last question on this piece of paper, Duan Yun couldn't help but be stunned for a moment.