Just then, Gu Zhiyun lifted the curtain and came in, and the old man and the young man stared at each other.

Gu Zhiyun, being well-mannered, was quite surprised that Old Man Xu was still there, but still politely said:

"Hello, Grandpa."

Old Xu sat cross-legged on the kang with an air of composure, took out his reading glasses, put them on, and squinted as he scrutinized Gu Zhiyun.

"Hey kid, this is a young lady's room. How dare you just barge in like that?"

Gu Zhiyun was a little unhappy: "Grandpa, you're a man too. Didn't you just sit on that young girl's bed and not leave?"

Old Xu puffed out his chest confidently: "This is my granddaughter's room, why can't I sit on my granddaughter's kang (heated brick bed)?"

Gu Zhiyun retorted, "I'm Jingya's boyfriend, and both sets of parents have given their approval. Why can't I go into Jingya's room?"

Upon hearing this, Old Man Xu immediately beamed with joy: "Hehe, so you're my granddaughter's husband! Our Jingya has excellent taste; I could tell you're destined for great things!"

Gu Zhiyun resisted the urge to roll his eyes: "When did Jingya become your granddaughter?"

Old Xu said matter-of-factly, "Look at what you're saying! Jingya has always been my granddaughter!"

Gu Zhiyun thought to himself, "You really know how to claim kinship. Why not go to someone else to claim a granddaughter, but instead you have to come to Jingya?"

Old Xu greeted Gu Zhiyun warmly, like a senior director: "Come, come, grandson-in-law, sit down and have some melon seeds, don't be shy."

Gu Zhiyun: "..."

He suddenly noticed a thick stack of scratch paper next to Old Man Xu, covered with calculations in advanced mathematics.

Seeing that he was staring at the manuscript paper, Old Xu generously took out the manuscript paper himself.

"Grandson-in-law, did you go to university? I'm planning to compile a university-level mathematics textbook. Can you understand it?"

Old Xu said this so casually, as if he were saying he wanted to eat cornbread tonight.

These words, however, gave Gu Zhiyun quite a shock.

He took the manuscript and examined it carefully. Some of the formulas were familiar to him, while others were not. He remembered that his parents had also written similar formulas when they were studying aerospace knowledge.

Gu Zhiyun was overjoyed. His gaze towards Old Man Xu completely changed. It was as if he had dug up a stone, brought it home, and discovered that the stone was actually a beautiful jade!

He pulled a piece of paper from his pocket and handed it to Old Man Xu: "Grandpa, can you take a look at this? I can't figure out the answer to this problem. What's wrong with it?"

Old Xu glanced at it only once before pointing to a certain step in his calculation and saying, "Here, there's a mistake in the calculation here."

Old Xu took the pencil and wrote down the correct calculation formula next to it.

"How about you calculate it again this time?"

Gu Zhiyun quickly took the pencil and began to do some calculations.

Sure enough, the correct answer was obtained smoothly!

This time, he was not just surprised, he was overjoyed!

"Grandson-in-law, judging from your appearance, are you preparing for the college entrance examination?"

Gu Zhiyun nodded: "You also know that the college entrance examination has been reinstated?"

Old Xu nodded proudly: "I was one of the first to know that the college entrance examination was going to be reinstated!"

Upon hearing this, Gu Zhiyun felt a slight suspicion arise in his heart.

This old man not only has sharp eyesight and a clear mind, but also possesses logical thinking strong enough to write university textbooks. He speaks with great clarity of thought, and doesn't seem like someone with dementia at all.

Would someone who remembers even complex mathematical formulas perfectly forget who they are, what their name is, and where they live?

Seeing Gu Zhiyun's shifty eyes, Old Xu seemed to have guessed what he was thinking and muttered with a pout:

"I've already said that Alzheimer's disease doesn't affect intelligence. I've had Alzheimer's for several years, but I haven't forgotten any of my math knowledge!"

"Dinner's ready!"

Shen Jingyan walked in carrying steamed brown sugar buns. When she saw Gu Zhiyun, she naturally leaned against him and said sweetly, "Brother Yun, why don't you have dinner here?"

Old Xu hurriedly asked, "Is the food you made enough?"

He said calmly with a smile, "Don't worry, even if you were Pigsy from Journey to the West, I could still fill your belly!"

Old Xu beamed with joy: "That's good, that's good!"

At the dinner table, while eating, Old Xu took out a stack of manuscript paper and handed it to Shen Jingyan.

"Jingya, these are the questions I gave you. You got all the questions this afternoon right. Starting tomorrow, you can start learning sets!"

Gu Zhiyun frowned slightly upon hearing this: "Grandpa, sets are high school math, while Jingya is currently learning junior high school math."

Old Xu didn't take it to heart: "My granddaughter is smart, her level has long surpassed junior high school, what's wrong with her learning high school knowledge earlier!"

Chen Jingyan smiled and put away the manuscript.

Gu Zhiyun was a little unhappy.

Tutoring Jingya was the sweetest time for the two of them, which he cherished and enjoyed. Why did an old man come along and seem to be taking over the role of the host?

What if Jingya thinks that Old Man Xu is a better teacher and wants to switch to Old Man Xu for tutoring?

After dinner, Gu Zhiyun pulled Shen Jingyan outside and asked in a low voice, "Jingya, this old man seems to be clinging to you. Are you just going to keep supporting him like this?"

Shen Jingyan said with some difficulty, "It's probably because I saved him. He is very dependent on me. It's not realistic to keep taking care of him forever. But the doctor said that Alzheimer's disease is intermittent. Maybe in a few days, Grandpa will remember who he is."

Gu Zhiyun said, "This old man is no ordinary person. I think he looks like a university professor. I'll call my parents later and ask if there's a professor surnamed Xu in the universities in Beijing who teaches mathematics."

Shen Jingyan thought this was a great idea.

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