The milk tea on the table was steaming, and outside the floor-to-ceiling window, a few clumps of green bamboo were swaying in the wind.

Lin Chaoxi stared at the milk tea cup for a while, and thought that the air conditioning in the library might be turned on too high. She blushed from the heat.

The pause was too long, and Lin Chaoxi coughed: "The plot of this movie is roughly like this... In the future, there is an organization that prevents crime, which subverts our current mechanism for punishing crimes that have already occurred..."

"Um."

"This agency uses some means to arrest people who want to commit crimes but have not yet committed crimes."

"How?"

"Through three 'prophets', um... three people who can sense criminal intent. They babble a lot of vague things every day... Then the crime prevention team can read their 'prophecies' and prevent crimes in advance..."

“How much has the crime rate dropped?”

"Felony crime rate is down 99.8%, with only one homicide in five years."

Pei Zhi pondered for a while and said, "It is indeed very metaphysical."

Lin Zhaoxi didn't know why she suddenly thought of this movie, but since she had started talking about it, she had to continue. She swallowed her saliva and asked tentatively: "Do you think that through mathematical calculations, is it possible to calculate what will happen in the future, just like what is said in this story?"

Holding up the milk tea, Lin Chaoxi was waiting for Pei Zhi.

"This is a big question." Pei Zhi thought about it seriously and answered her.

"Or to simplify the problem..." Lin Chaoxi paused, "For example..."

"Like what?"

"Hmm..." Pei Zhi was too smart, Lin Chaoxi suddenly decided to play tricks, "How about you give me an example, I can't think of one."

"For example, there is a criminal who we know has the intention to launch a terrorist attack, but we don't know the specific intention and location of the attack."

"Yeah, that's it. If we want to calculate it mathematically, what kind of knowledge do we need... should we start with calculus?"

"The order should be single variable calculus, linear algebra, probability theory, multivariate calculus..." Pei Zhi paused, "But single mathematics, I'm afraid it won't work."

"oh……"

"With the help of computers, there should still be hope."

Lin Zhaoxi's eyes lit up. Yes, she seemed to have been missing a great thing.

"A date on the first day of the new year?" Suddenly, a long sigh came from behind.

Lin Chaoxi turned her head suddenly and found Old Lin standing behind her. She was shocked and felt like she was caught in a premature love affair.

"We are discussing some issues." Pei Zhi said frankly.

"What's the problem?"

"You followed me!" Lin Chaoxi felt guilty and interrupted Pei Zhi and Lao Lin.

"Why do you say that?" Lao Lin laughed.

"You follow me to the library."

"How can you call me a follower?" Lao Lin dragged a chair and sat down casually at their table. "Besides, it was clearly Pei Zhi and I who made the appointment first."

Lin Chaoxi choked on a mouthful of milk tea: "Ahem!"

Pei Zhi handed over a tissue and Lin Chaoxi wiped his mouth: "Did you secretly open the stove without telling me on New Year's Day?"

"Master..." Pei Zhi said helplessly.

"I called her, but she said she had something to do and let me play alone," said Lao Lin.

Lin Chaoxi was stunned. It seemed like there was a moment when she and Lao Lin finished breakfast. Lao Lin asked her what plans she had for the day and whether she wanted to celebrate the holiday together...

She said: No, I have something to do...

"Then why did you ask us to come to the library to celebrate the holiday today?" Lin Chaoxi asked.

Lao Lin: "You are changing the subject so bluntly. Dad really can't answer you right now."

"..." Lin Zhaoxi, "I'm sorry."

"It doesn't matter."

Lin Zhaoxi: “…”

"I'm here to fulfill your New Year's wish," said Lao Lin.

Looking at Old Lin's face that said "Dad knows everything", Lin Chaoxi's heart skipped a beat nervously. She didn't know what she had exposed.

"What did you say?"

"Don't you want to listen carefully to your father's teachings in the new year? Don't you want to learn calculus?" Old Lin smiled and looked very proud.

Lin Chaoxi was stunned. She felt that she should be moved. She had asked Lao Lin too many questions before, and Lao Lin took them to heart. He discovered her thoughts through clues...

But now, she has a strange sense of fatalism.

"I will study hard." She said very seriously.

Lao Lin smacked his lips and turned to look at Pei Zhi: "Give her a few questions?"

Pei Zhi was stunned, not knowing what was going on.

"Give her a hard time."

After hearing this, Lin Chaoxi was still confused. But Pei Zhi understood. He nodded, took out a piece of white paper and a pencil from his schoolbag, and really started to ask questions.

Lin Chaoxi moved forward in fear, not knowing what Old Lin and Pei Zhi were doing. He could only peek at Pei Zhi as he was asking questions.

The first question was factoring, which was very basic. He got the answer by mental arithmetic, and Lin Chaoxi breathed a sigh of relief.

The second question is to find the roots of a quadratic equation, and the third question is an algebraic proof...

After the algebra-related part, Pei Zhi started to ask questions about functions, then geometry, trigonometric functions, and complex functions...

He held the pencil and wrote carefully and steadily. Lin Chaoxi watched him finish one sheet of paper, then took another one without any mercy.

"What do you think?" asked Lao Lin.

"This is..."

"Can you trick Dad into giving the answer by just drawing out the tone?"

Lin Zhaoxi: “…”

“Is this the basis?”

"Be more specific." said Lao Lin.

“The basics of secondary school mathematics that should be mastered before studying advanced mathematics.”

"Although the mathematics you learned in middle school and college..."

"It doesn't matter at all." Lin Zhaoxi added, "I will still be brave enough to answer the questions."

"But?" Lao Lin was about to turn around.

"But you have to understand why they are unrelated."

Pei Zhi raised his lips with great difficulty, probably because he felt that her answer was very much like Lao Lin's.

Lao Lin nodded nonchalantly and asked Pei Zhi to bring the questions.

Lin Chaoxi then realized that Pei Zhi had written three full pages of questions without realizing it.

There are proofs and analyses, as well as a very complicated function problem...

"This question is quite interesting." Pei Zhi explained.

Lin Zhaoxi: “…”

Being stared at by two people on both sides, Lin Chaoxi didn't even have the strength to resist.

The New Year's date was to do homework, and she thought it was normal. She picked up the pencil in front of Pei Zhi and said, "Give me some more blank paper."

——

For two whole hours, Lin Chaoxi sat on the small sofa in the café and wrote non-stop.

The questions asked by Pei Zhi were just like him, very organized and yet very profound. Some of the proof questions seemed simple, but actually involved a lot of knowledge application, so she also needed to think carefully.

Unconsciously, time passed by minute by minute, and Lin Chaoxi was immersed in it. The moment she put down her pen, she took a long breath and felt that the college entrance examination might be just like this.

She began to arrange the answer sheets on the glass table, read them all over, and then prepared to hand them in.

Lao Lin said, "Keep it for yourself. It's time to eat."

After saying that, Lao Lin took the lead, pushed the chair away and ran away.

Lin Chaoxi asked Pei Zhi in a low voice: "Master, what's wrong? Will you mark my paper?" She was ready to hand in her answer sheet sincerely and wait for inspection.

"Master is watching you while you do it."

"…So it's okay?"

"Um."

"Then why is he running?"

Pei Zhi continued helplessly: "I want to go to the toilet."

Lin Zhaoxi: “?”

Pei Zhi began to pack up. The heating in the small coffee shop was sufficient. Lin Chaoxi looked at the table and took a while to react. Finally, she understood: she was immersed in doing the questions just now, and Mr. Lin was actually looking at her nervously the whole time. He waited for as long as she did.

Perhaps for Lao Lin, this is the test that he values ​​the most. As it is a major test of all high school mathematics knowledge, coupled with the meaning of a new year and a new atmosphere, it is particularly important.

"Why didn't you say so earlier!" Lin Chaoxi rubbed her face. It was still scary when her father would make such surprise attacks. She was glad that she had done the questions seriously just now.

"Master said..."

"What?"

"I was afraid that you would cheat with the questions if you knew about it earlier..."

"Why am I such a person?!" There was still a large cup of milk tea left that Pei Zhi ordered. Lin Chaoxi picked it up with a distressed look, wanting to take a few more sips before leaving.

"It's cold, don't drink it." Pei Zhi said.