At eight in the morning, Jiang Yubai appeared punctually. When he saw Lin Zhixia, he naturally took her hand and told her, “I dreamed about you last night.”

“What was I doing in your dream?” Lin Zhixia asked curiously.

Jiang Yubai avoided answering. He asked about Lin Zhixia’s research progress, and Lin Zhixia exposed him: “Are you changing the subject?”

He admitted: “Yes.”

Lin Zhixia held onto his arm and continued to investigate: “What did you dream about? Tell me quickly.”

Jiang Yubai began to stall: “Let’s talk about it when we get to my house.”

And so, Lin Zhixia followed him home.

They walked through a corridor, passing a music hall where a grand piano stood. Lin Zhixia glanced around, and Jiang Yubai pushed open the side door of the music hall.

Lin Zhixia followed him step by step, like a small tail that wouldn’t shake off. She said, “I want to hear ‘Autumn Whispers,’ play it for me.”

Jiang Yubai began to play “Autumn Whispers.” He hadn’t touched the piano for more than two months and was trying to find his touch. He didn’t open the grand piano’s huge lid, making the melody sound deep and gentle.

Lin Zhixia stood beside him, observing.

His piano playing suddenly stopped.

He wrapped his arms around Lin Zhixia’s waist and, with a slight effort, lifted her. Her feet were suspended in the air, she felt a bit scared, but didn’t struggle, only asking him: “What are you trying to do?”

Jiang Yubai let her sit on the piano lid. She asked in return: “Won’t I break your piano by sitting on it?”

“You’re so light,” Jiang Yubai said, “it’s impossible to break it.”

Lin Zhixia thought: I weigh over forty kilograms.

In front of the floor-to-ceiling window, trees flourished, and the thin gauze curtains filtered down tiny bits of green shadows, coincidentally projecting them onto the pure black piano lid.

Jiang Yubai sat back on the piano bench, playing the interrupted melody with only his right hand. His left hand grabbed Lin Zhixia’s wrist. She watched him lower his head, kiss the back of her hand, and then kiss her fingertips.

He said, “This was my dream last night.”

In this moment, he gripped her fingers tightly, and his emotions ran deeper.

Lin Zhixia did not give any response.

She jumped down from the piano lid, her hand numb, her legs weak, her thoughts confused. She suddenly realized that many things simply couldn’t be simulated through imagination alone. For instance, she had read famous literary works from ancient to modern times, both Chinese and foreign, but she had never understood why intelligent and clever protagonists often stumbled badly on the path of pursuing love.

Now, she tasted that peculiar flavor of being beyond her control.

Lin Zhixia’s heart was beating as fast as a drum.

Jiang Yubai thought she would say something, but she was very quiet. He suspected that his actions were still somewhat abrupt. To break the silent atmosphere, he suggested: “Let’s go to the study to learn.”

Lin Zhixia hurriedly agreed: “Alright.”

Jiang Yubai extended a hand to her. She immediately took it, their fingers intertwined, and they went to the study.

The study had excellent lighting, with row upon row of towering bookshelves, like a small library. The carpet on the floor was embroidered with intricate patterns, and a black ebony desk by the window held a computer and a stack of papers. Beside the desk were two ergonomic chairs with adjusted heights—clearly seats for Jiang Yubai and Lin Zhixia.

Lin Zhixia sat down slowly, saying with authority: “You sit too. From now on, I’m the teacher you’ve hired.”

“Teacher Lin,” Jiang Yubai recited.

Lin Zhixia nodded: “Yes, we need to look like we’re studying when we study. While I’m tutoring you, call me Teacher Lin, don’t change your form of address.”

Jiang Yubai pushed the edge of the desk, the chair’s wheels sliding, bringing him closer to Lin Zhixia: “Teacher Lin, have you taught other students before?”

“Yes,” Lin Zhixia opened a textbook, “don’t worry, I have extensive teaching experience.”

The more Lin Zhixia tried to maintain a strictly professional demeanor, the more Jiang Yubai wanted to cross the safety line of the “tutor and student” relationship. He said, “The students you taught before were probably your classmates, and their foundations were all better than mine.”

Lin Zhixia stared at him suspiciously.

In fourth grade, he often compared grades with her.

After entering university, he claimed, “Your classmates’ foundations are better than mine.”

Was Jiang Yubai coming to her for tutoring, or was he playing a role-playing game with her?

One of Lin Zhixia’s greatest hobbies was role-playing. She was excited and patiently cooperated: “Don’t rush, each course has limited key points, and your potential is unlimited.”

Jiang Yubai took out a course material and placed it in front of Lin Zhixia.

Lin Zhixia casually flipped through it and saw that the last page’s index listed the mathematical foundations needed for this course, including linear algebra, advanced mathematics, probability theory, and statistical methods. Each category was annotated with specific knowledge points; for example, the probability theory section included “Expectation and Regression Function,” “Law of Large Numbers and Central Limit Theorem,” and a lot of other content.

Lin Zhixia asked very responsibly: “First, tell me which parts you don’t understand?”

Jiang Yubai picked up a pen: “I’m not sure what I don’t understand.”

Lin Zhixia and Jiang Yubai had been deskmates for a full four years. She had taught him many times and had written a problem-solving notebook for him. Since graduating from middle school, she had never tutored him hands-on again.

She missed those days.

She said more seriously: “Alright, explain it to me once, starting from the first knowledge point…”

Jiang Yubai started from “regression function,” and when he got to “central limit theorem,” his pen fell on the desk. So he paused and, pointing to that line of English, asked softly: “Teacher Lin, what is the central limit theorem?”

He didn’t understand the “central limit theorem”?

Lin Zhixia summarized simply: “This paper uses the most common expression of the central limit theorem. Suppose you have a distribution containing independent random variables, the number of random variables is finite, the average is M, the variance is D, you extract multiple sets of samples from this distribution, each set takes an average value a, after standardization, a1, a2….an will converge to a normal distribution.”

She glanced at him: “The central limit theorem is one of the most important theories in ‘Probability Theory,’ and we can continue to expand on it. You’ll find that samples from the Cauchy distribution don’t apply to this theorem. Why is that?”

Jiang Yubai’s right index finger lightly tapped the desktop: “Teacher Lin.”

“What is it?” Lin Zhixia blinked.

Jiang Yubai’s voice was particularly pleasant: “Could you…”

“Hmm?”

“Sit on my lap.”

Hearing his request, Lin Zhixia was stunned for a second.

Jiang Yubai gave his reasons. He said Lin Zhixia would be closer to him, and he could hear more clearly. When he wrote in his notebook, Lin Zhixia could add content beside it, making their error-checking more efficient.

Lin Zhixia remembered how she once used a feather to tease Jiang Yubai’s little cat. At this moment, all of Jiang Yubai’s words turned into a feather, falling on her heart.

She held his shoulders, stood up, and sat on his lap.

Before Lin Zhixia was settled, Jiang Yubai’s left arm wrapped around her waist, his right hand still holding a pen. He politely reminded her: “We were just talking about the Cauchy distribution, Teacher Lin.”

Teacher Lin’s breathing was irregular: “Yes, I remember.” Then said: “I’ll give you a problem. If you answer correctly…”

“Is there a reward?” Jiang Yubai asked with her ear.

“I’ll give you a kiss,” Lin Zhixia declared.

*

Last night, Jiang Yubai had a dream.

He not only dreamed of the scene in the piano room but also dreamed of Lin Zhixia sitting on his lap. So far, his dream had come true. Lin Zhixia not only showed no rejection but was willing to play the “if you answer correctly, I’ll kiss you” game with him.

Jiang Yubai laid out a draft paper and politely asked Teacher Lin to pose a question.

There was only one pen on the desk, held by Jiang Yubai. Lin Zhixia touched his index finger, gently scratching it, and he immediately gave her the pen. If one ignored his left arm around her waist, he was a cultured and well-mannered student.

Lin Zhixia wrote the probability density function of the Cauchy distribution in the paper. Before she finished writing, Jiang Yubai asked her: “Are you still teaching me the central limit theorem?”

“Yes,” Lin Zhixia released the pen.

This was her first time teaching while sitting on Jiang Yubai’s lap. Her mind was filled with many thoughts and fantasies, but how could she calm down to explain problems to him?

She asked a very simple question: “You’ll find that samples from the Cauchy distribution don’t apply to this theorem. Why is that?”

If Jiang Yubai answered correctly, Lin Zhixia would kiss him. She hadn’t set detailed rules, nor had she mentioned an upper limit on rewards, meaning Jiang Yubai could continuously ask for kisses—what would happen after that? He feared he wouldn’t be able to control himself.

Jiang Yubai pondered for a moment, killing all improper thoughts in their budding state. He replied: “I’m sorry, Teacher Lin, I’ve never studied the Cauchy distribution.”

He said this very sincerely.

Lin Zhixia believed him.

She hadn’t expected Jiang Yubai’s mathematical foundation to be so weak.

She meticulously explained the Cauchy distribution, mentioning that one of the constraints of the central limit theorem is that the probability density function’s mean and variance exist and are finite, therefore, the Cauchy distribution doesn’t apply to the central limit theorem.

Lin Zhixia added further explanation: “The result of grouped sampling from the Cauchy distribution after mean normalization…”

Jiang Yubai continued: “The result is not a Gaussian distribution, it’s a Cauchy distribution.”

“Correct!” Lin Zhixia was pleasantly surprised.

Lin Zhixia thought her teaching was very successful.

As Jiang Yubai’s home tutor, Lin Zhixia was dedicated to her job, conscientious, and kept her word. She quietly turned her head and kissed his cheek.

Jiang Yubai remained silent, slightly raising his chin, his gaze falling on the distant bookshelf. He tightened the hand around her waist, but he didn’t even call her “Teacher Lin” anymore. Lin Zhixia thought he was very interesting, making her unable to figure him out, with reactions that were all difficult to predict.

Lin Zhixia sat sideways on his lap, her hands around his neck, staring at his Adam’s apple.

Lin Zhixia possessed a vibrant and strong curiosity. Jiang Yubai had an Adam’s apple, while she didn’t, so she wanted to know what it felt like to have such a thing. She approached his neck, warm and subtle breath flowing past his neck. He didn’t speak, nor did he stop her.

When they first started playing the “tutor role-playing game,” Jiang Yubai had many scenario settings and dialogue modes. But now, he transformed into a yielding sculpture, quiet, composed, and as cold as frost, like someone enshrined in a noble and sacred hall.

Lin Zhixia found it increasingly fascinating, indescribably wonderful.

She lightly kissed the protrusion on his neck, as if touching an incredible switch. Jiang Yubai gripped the armrests of his chair tightly and called her again: “Teacher Lin.”

This was so much fun.

Their role-playing game continued.

Lin Zhixia carefully articulated: “I… I never took the college entrance exam, I’m not good at biology…”

She was about to say, “You teach me biology,” when Jiang Yubai interrupted her: “How can someone who never took the college entrance exam be a home tutor?”

This question stumped Lin Zhixia.

Lin Zhixia confidently told him: “Many of my undergraduate classmates were admitted without exams, as was I.”

Jiang Yubai finally turned the topic in a normal direction. His once-tense nerves relaxed a bit, and he didn’t lose his composure in front of Lin Zhixia. He very much wanted further contact with her, but he ultimately restrained himself. He calmly said, “Teacher Lin, let’s continue studying.”

Lin Zhixia’s thought process was completely different from Jiang Yubai’s. She very directly asked him: “When I kissed you, what did you feel? Tell me, I want to know. I want to write your words in my diary.”

Jiang Yubai opened a paper. He translated the English into Chinese, softly reading an abstract, as if treating the paper as a “Heart-Clearing Incantation.” Lin Zhixia said, “You still won’t answer me, this is a teacher’s order.”