I really don't want to lie down and win

I'll ask later.

The professor started to solve Xu Mang's problem by himself, but soon he discovered the problem. Although it was an algebra problem, he couldn't find a breakthrough.

after that,

The professor tried a complicated solution, and finally spent 7 minutes, and then reversed the answer based on the answer to get a relatively simple process, and it happened to be the end of class at noon.

Seeing that Xu Mang was about to leave, the professor hurriedly stopped him.

"classmate!"

"Wait a minute!" the professor shouted at Xu Mang, "Are you still coming this afternoon?"

"Uh..."

"Come on!" Xu Mang nodded, and said with a smile, "The professor unlocked it?"

"Untangled."

"But I want to know what your answer is. Let's talk about it this afternoon," said the professor.

"Oh."

...

noon,

Xu Mang and Yang Xiaoman were eating in the school cafeteria. The five of them were curious about the conversation between Xu Mang and the professor, but no matter how they asked, Xu Mang kept smiling and didn't tell anyone about the conversation with the professor. things, including Yang Xiaoman.

For this,

Yang Xiaoman was very unhappy, a little emotional.

The main reason is that it's a bit embarrassing...it's my boyfriend, but I keep it a secret from myself...in front of so many people.

at the nearby Starbucks,

Yang Xiaoman ordered a cup of hot fruit tea, and sat on the chair without saying a word, with three large characters of unhappiness written all over her face.

Yang Xiaoman: #￣￣#

"..."

"What?" Xu Mang was playing with his phone, looked up and saw this scene, and asked strangely, "Who bullied you? Tell me... beat him into a pig's head!"

Yang Xiaoman glanced at it, and said angrily: "Then you can beat yourself."

"..."

"So it's me?" Xu Mang suddenly realized, and said helplessly, "I'm pretty honest today..."

"Humph!"

"You make me unable to step down in front of others." Yang Xiaoman said angrily.

Xu Mang frowned, counting the days... Today seems to be the day when Xiaoman comes to relatives, so I can't afford to mess with him... Last time I suffered a big loss.

In the face of a woman who comes to relatives, the best solution is to not speak and endure her little emotions silently, because at this time, no matter what you do is wrong, there is no way... there will always be so many times a month. God is irritable.

After crackling and complaining, Xiaoman got emotional release.

"Xiaoman?"

"Uh?"

"Did you... visit relatives?" Xu Mang asked cautiously.

"..."

"It seems that he came here in the middle of the night last night. I was scared to death this morning." Yang Xiaoman suddenly asked mysteriously: "By the way, how do you count my life so clearly? Do you have any bad intentions?"

"no!"

"Hehe... drink tea, drink tea."

quickly,

It's afternoon time.

Xu Mang rushed to the front and happily came to the training classroom, only to find that the professor was already there.

"Hello Professor."

"Come here?" Seeing Xu Mang coming, the professor nodded and said, "Come and see my problem-solving process, right?"

"Oh..."

Xu Mang picked up the professor's problem-solving process and read it carefully. There were basically no mistakes, and then he said seriously: "Professor...you are worthy of being a master in the field of mathematics. You are completely correct and there are no mistakes."

"At first I couldn't solve it, then I went around a big circle, and finally reversed it, and got the simplest process." The professor looked at Xu Mang and said seriously, "Your ability to come up with questions impresses me!"

"Hehe..." Xu Mang smiled, "I'm just a student."

"By the way, what's your name..."

Halfway through the professor's speech, Yang Xiaoman and others came to the classroom. Immediately, the professor stopped talking, and said silently: "Let the contestants do the problem first, and then you can help them analyze the process and solve the problem yourself."

"Oh."

Xu Mang returned to his seat in the last row and lay down on the table.

"Cough cough!"

"I'll give you an hour to solve a math problem!"

words fell,

The professor wrote down the topic on the blackboard.

Use Z to express the set of all integers, and find all functions f: ZZ, satisfying that for any integer a and b, there is f2a2fbffab

at this time,

Everyone present was stunned, including Yang Xiaoman.

This...

What function is this?