Tang Dynasty: Starting at Xuanwu Gate, this prince is better off not being one.

"Kid, what are you doing?"

The scene before him left Li Er dumbfounded.

Inside the Ministry of Works' office, dozens of people of all ages were sitting.

Among these people were officials in their forties and fifties, as well as those in their twenties and thirties, and even a few children as young as seven or eight, who were struggling to hold pens and shakily writing something on paper.

"Greetings, Your Majesty!"

When these people saw that Li Er had actually come here, they all knelt down on the ground.

Li Yu stepped forward with a smile to pay his respects, and then explained, "Your Majesty, I once presented you with a book, saying that I wanted to teach the officials of the Directorate of Works mathematics. And here they are."

Li Er looked the group of people over, then said with an incredulous expression, "Boy, don't try to fool me. There are so many officials in the Imperial Workshops?"

Upon hearing this, Li Yu chuckled and said, "Hehe! It's because they see that my nephew is very good at teaching, so not only officials from the Directorate of Works, but also officials from the Ministry of Works have come. Among them are their sons and nephews, who are also learning mathematics from my nephew."

"..."

Li Er was somewhat skeptical of Li Yu's words. After all, mathematics was such an obscure and difficult subject that even those who mastered it would not be given important positions in the court. He found it hard to believe that so many people would be eager to learn such a subject.

Seeing that Li Er seemed unconvinced, Li Yu knew that he had never thought highly of mathematics, so he explained, "Your Majesty, you mustn't underestimate the importance of mathematics!"

"How so?" Li Er asked, raising an eyebrow.

"Let me tell you this, nephew: the reason why those guys at the Imperial Observatory can understand celestial phenomena is inseparable from mathematics; the reason why Master Yuan Tiangang and others can use divine calculations to predict the unpredictable is also due to mathematics."

At this point, he swallowed hard and continued, "Moreover, if our Great Tang Dynasty wants to develop further, mathematics is of paramount importance!"

Hearing Li Yu's serious tone, Li Er narrowed his eyes: "Boy, stop exaggerating. What does the strength of our Great Tang have to do with mathematics?"

"This is of great importance!" Li Yu said. "You see, the taxes levied by various prefectures and counties require arithmetic, the land allocation by the Ministry of Revenue also requires arithmetic, and even the army needs arithmetic to fight battles."

"Does war also require mathematics?" Li Er asked, puzzled.

"That's right." Li Yu nodded. "Let me explain..."

Li Er raised his hand to interrupt Li Yu before he could speak, then glanced indifferently around.

Having been in officialdom for a while, the people around him immediately understood Li Er's signal and led their nephews and nieces out of the office. Thus, for a moment, only Li Yu and Li Er and his wife remained in the office.

"Boy, now you can talk. I want to see what you can come up with," Li Er sneered.

Upon hearing this, Li Yu cleared his throat and sat up straight, saying, "Uncle, I know a field of knowledge that encompasses everything, from the small things like bowls and chopsticks people use every day to the changes in all things in the world. Even the mechanical science of the Mohists is only a small part of it."

"That is why I call it 'the principle of nature,' or 'physics.'"

"Physics?" Li Er couldn't help but feel curious after hearing Li Yu's seemingly profound explanation.

"That's right, it's physics," Li Yu said. "Uncle, if I may be so bold as to ask you, if you were to lead three thousand soldiers clad in gleaming armor and wearing double stirrups to fight against Xiang Yu's fifty thousand elite troops, what do you think your chances of victory would be?"

After a moment's thought, Li Er said, "Seventy percent. Yu's bravery is unparalleled throughout history. But if we follow your conditions, I have at least a seventy percent chance of winning."

"Hmm." Li Yu nodded with a smile, then continued, "If I may be so bold as to ask again, if all this equipment were simultaneously distributed to Xiang Yu's iron cavalry, what would your chances of victory be?"

Upon hearing this, Li Er hesitated for a long time before replying with a dark face, "One...one-tenth, boy, just say what you want to say. Trying to keep me in suspense, you must be asking for a beating!"

As soon as she finished speaking, Changsun, who was standing to the side, couldn't help but cover her face and chuckle when she saw her husband's embarrassed and angry expression.

Li Yu scratched his head, somewhat embarrassed, and said, "Uncle, all I want to say is that as long as the equipment is good enough, it can greatly affect a war that is originally evenly matched. For example, if two people with similar skills fight, one with a weapon and the other unarmed, the loser will be the latter without any surprise."

"I admit you have a point, but what do you have to do with mathematics?"

Seeing that he had laid the groundwork enough, Li Yu began to get to the point: "The physics that my nephew mentioned is based on mathematics. Whether it is mechanical engineering or weapon manufacturing, it requires precise calculations. If there are fixed data calculated by mathematics, then the speed at which our Great Tang Dynasty manufactures weapons and armor will increase several times over."

"Stop talking nonsense!" Upon hearing Li Yu mention military industry, Li Er immediately sat up straight and reprimanded him, "Do you know that only the Empress and I are here? If there were others present, and you were to say these things to me and then fail to deliver, that would be the crime of deceiving the Emperor?"

"Of course I know that," Li Yu chuckled. "It's precisely because it's just you and Auntie here that I dare to boast so much. But what I'm saying isn't entirely nonsense. Do you still remember the smoke bombs and the salt-making method?"

"I know. Could it be that these two are also what you meant by 'physics'?"

Li Yu nodded. "These all come from the field of 'physics,' but this is just a small part of it and not worth mentioning at all."

Upon hearing this, Li Er was so startled that he stood up from his chair: "You're saying these things are insignificant?"

"Indeed, it's nothing to mention," Li Yu said. "These are just some superficial things. My nephew only needs to demonstrate them once, and others can easily imitate them. But the truly profound things require hundreds or thousands of calculations to achieve any results."

At this point, he changed the subject: "Of course, this achievement is far beyond what smoke bombs or salt production can achieve."

Li Yu's words silenced Li Er.

Whether it's salt production or Li Yu's brewing, the wealth generated by these two things is already immeasurable, not to mention the smoke bombs, which Li Er had used against Wang Shichong and Dou Jiande, and at Xuanwu Gate, with remarkable effectiveness. But if these things are just the tip of the iceberg, Li Er finds it hard to imagine just how incredible the "achievements" Li Yu speaks of truly are.

After pondering for a while, Li Er turned his head to look at Li Yu and found that the boy was looking at him expectantly, which made him feel very uncomfortable.

He narrowed his eyes and sneered, "Boy, what are you up to? You're saying all this for no reason; you're probably trying to get something from me..."

.........