Old Cheng was already stunned. He probably never dreamed in his wildest imagination that there were people in this world who studied such things. His mouth hung open, unable to speak.

Seeing Old Cheng dumbfounded, Yun Ye hurriedly shook his arm. Only then did Old Cheng come back to his senses and couldn’t help but ask: “What else did he teach?”

“Mathematics, physics, geometry, mechanical drafting, map making, metal casting, and so on—various minor subjects.” Yun Ye recited in one breath all the knowledge he had learned in school.

“Which discipline does salt-making belong to?”

“Physics. Simple dissolution, filtration, detoxification, evaporation, and crystallization produce salt. In short, physics is a discipline that studies the laws governing all things in heaven and earth. Allow your nephew to demonstrate them to Uncle one by one in the future.”

“This old man can see them? Does your master’s school really have no restrictions in this regard?”

“Learning, learning—one must study while asking questions. What can one person accomplish alone? When my teacher instructed me, he told me that once I had the opportunity, I must spread the knowledge of our school throughout the world. The chaos in the realm has ended, and this is precisely the beginning of civil governance. After years of turmoil and chaos, who knows how much of our Han culture has been lost? These are all the painstaking efforts of our predecessors and the wealth of future generations. How can this not break one’s heart? How dare this young man keep it private?”

“This old man is a crude person who looks down on those sour scholars with their ‘zhi hu zhe ye,’ but for those truly learned great scholars, this old man dares not show the slightest disrespect. There are indeed several such people in Chang’an. When we return, this old man will take you to call on them. For Old Cheng’s sake, they will surely instruct you. Old Cheng here waits to see the day your learning reaches great achievement. Since you’ve studied mathematics, let me call over several military accountants to test what level you’ve reached. How about it?”

Seeing that Old Cheng wanted to test him, Yun Ye laughed inwardly. In this Tang Dynasty era where “Three-Fold Well, Chickens and Rabbits in the Same Cage, and Han Xin Counting Troops” were all considered super difficult problems, Yun Ye didn’t believe there was any difficult problem that could stump him.

“Uncle, you might as well call several people and prepare several difficult problems. It doesn’t matter if it takes more effort—your nephew hasn’t eaten yet.”

Seeing Yun Ye’s arrogance, Cheng Yaojin rarely didn’t get angry. He casually pulled out a jade pendant from his bosom.

Green jade? Yun Ye recognized at a glance that it was the legendary supreme quality mutton-fat white jade. In later generations, you wouldn’t even ask the price without tens of millions. Suppressing the drool about to flow down, he asked: “Uncle wants to give it to your nephew?” As he spoke, he was about to reach out and take it, but Old Cheng withdrew his hand and tucked it back into his bosom.

“Want it? Win against three military accountants, and it’s yours.” After saying this, he lifted the tent flap and went out.

Yun Ye finally didn’t have to kneel anymore. The earlier kneeling position had nearly killed him—his thighs were unbearably sore and his buttocks felt swollen as if there were two of them. He carefully spread out his legs, sat down, picked up a piece of sauced meat and stuffed it in his mouth, chewing deliciously. It was actually beef! Wasn’t killing cattle in the Tang Dynasty a criminal offense? How could this old fellow slaughter cattle so freely? Thinking about it again, there probably wasn’t anyone foolish enough to run into the Left Martial Guard’s main camp to arrest cattle killers.

After a few bites of beef, two pieces of cooked mutton, and half a deer leg went down his stomach, Yun Ye suddenly felt life was so wonderful. Holding the teapot, he poured down half a pot of tea—Tang Dynasty raw tea, ground into powder, with a grassy smell rushing straight to his brain. He forced himself to drink it down, treating it as vitamin supplementation. Old Cheng hadn’t returned yet, and Cheng Chumo was also nowhere to be seen. Bored, Yun Ye pillowed his arm on the carpet and unknowingly fell asleep.

Yun Ye lay sprawled on the carpet, his snoring intermittent, occasionally mixed with sobbing sounds. Who knows what he was dreaming about—his face was streaked with tears.

Cheng Chumo quietly walked in. Seeing Yun Ye in this state, he shook his head and tiptoed to lift the tent flap and went out again.

Outside the tent stood a middle-aged scholar, hands folded in his sleeves, his face full of arrogance. He was already displeased that Cheng Yaojin had ordered him to compete with Yun Ye. Thinking that he himself had devoted nearly twenty years to studying mathematics, yet now had to exchange knowledge with this wet-behind-the-ears youngster—if not for the general’s order, he would have flicked his sleeves and left long ago. Who would have thought that when he condescended to come instruct this boy, the lad would be fast asleep, snoring away. Truly the conduct of one who is no filial son!

Cheng Chumo looked at the middle-aged scholar’s iron-blue face and felt displeased. My brother has been making salt for the entire army day and night without rest, and today he even traveled over sixty li. What’s impolite about a fourteen or fifteen-year-old child sleeping? This time has been hard on my brother—didn’t you see he’s still crying tears in his sleep? You sour scholar, besides writing and calculating, what other skills do you have? Thinking this, his expression became even more unpleasant.

“Captain, this youngster is truly impolite, feigning sleep to evade examination. Though I originally had the intention to instruct him, it seems rotten wood cannot be carved. I take my leave!” The middle-aged scholar paid no attention to Cheng Chumo’s gloomy face and cupped his hands arrogantly, preparing to withdraw.

Cheng Chumo reached out and grabbed the scholar’s sleeve: “Master Huang, please be patient. Since the general has already given the order, you’d better stay.”

“This boy is impolite, so his talent and virtue must be quite limited. A country bumpkin—is he even worthy of discussing mathematics? Since I tied up my hair and began studying, I’ve endured hardships to finally become a disciple under Master Liu at the Imperial Academy. After seven years of study, I’ve barely glimpsed the threshold of mathematics. Learning isn’t easy. For the general’s sake, Huang Zhien reluctantly agreed, yet suffered such great humiliation. Huang takes his leave!” Cheng Chumo had warned him using the general’s authority, but Huang Zhien could no longer suppress his anger. Flicking his sleeves, he turned to leave. Just as he turned around, he heard a lazy voice drift over.

“Studied for seven years—not easy. Can you solve the Nine Palaces Square? Do you know the Rope Measuring Well? Do you know the Pythagorean algorithm? How high is Mount Tai? How much sand does the Yellow River carry?”

Huang Zhien looked incredulously at Yun Ye leaning against the tent entrance and said in a trembling voice: “Two and four as shoulders, six and eight as feet, seven on the left and three on the right, wearing nine and stepping on one—this is the correct solution to Nine Palaces. The well’s depth is unknown, the rope’s length is unknown. Folded three times into the well leaves four chi remaining, folded four times into the well leaves one chi remaining. The well is eight chi deep, the rope is thirty-six chi long. The Pythagorean chapter of ‘Nine Chapters on the Mathematical Art’ says: base three, altitude four, hypotenuse five. I know that it is so, but not why it is so. How high is Mount Tai? How much sand does the Yellow River carry? Heaven knows.”

“Nothing under heaven cannot be measured. Measuring mountain height by mountain shadow, measuring the Yellow River by a bucket of water—does Master not know? According to Yun Ye’s knowledge, there are no fewer than five hundred methods to prove the Pythagorean theorem. What one learns should be applied flexibly. Otherwise, what’s the point of learning it?”

“How do you know this? How could you know this? The Imperial Academy keeps it secret and doesn’t show it to others. I merely heard my teacher mention it, yet you know it in such detail. What is the reason for this?”

“There are so many mathematics experts under heaven—why do you only know of the Imperial Academy? You can solve the Nine Palaces—can you solve the Sixteen Palaces? Can you solve the Thirty-Two Palaces? You know single variables, two variables—but do you know three variables, multiple variables? A few interesting problems, and you all treat them as treasures, keeping them secret and not sharing them. How laughable! These kinds of problems were merely games from my childhood. A frog at the bottom of a well vainly measuring the size of heaven—truly laughable.”

Huang Zhien felt his ears roaring. Some of what Yun Ye spoke were legends, some he had never heard of. He was an expert and knew that Yun Ye wasn’t speaking nonsense. Let alone himself—even if his teacher were here, he probably wouldn’t be much better off than himself.

Yun Ye strolled up to Huang Zhien, picked up a tree branch, and casually drew on the ground the Pythagorean Circle-Square Diagram and the Pythagorean Expansion-Square Diagram. Then he threw away the branch, dusted off his hands carelessly and said: “Today I was impolite first. The Pythagorean Circle-Square Diagram from the ancient sage Zhao Shuang and the Pythagorean Expansion-Square Diagram from my teacher—I’ll give them to you cheaply as an apology.”

Huang Zhien’s thoughts were already far from Yun Ye’s impoliteness. He lay prostrate on the ground, muttering under his breath, his fingers writing and drawing. Where would he still care about what Yun Ye and Cheng Chumo were doing?

Cheng Chumo gave Yun Ye a heavy slap: “Worthy of being my brother! I knew you wouldn’t lose to a sour scholar. Sure enough! Drinking alcohol is prohibited in the army, otherwise we brothers would get drunk together!”

Yun Ye rubbed his shoulder, his face full of resentment. This father and son—one slapping buttocks, one slapping shoulders, completely disregarding whether others could endure it or not. He quickly stopped the palm that was coming down again—any more slaps and he’d fall apart.

“Brother, your younger brother traveled all morning and reeks of sweat. It would be most impolite to see Uncle Cheng like this. It would be proper to let your younger brother bathe and change clothes first.” Only now did Yun Ye feel his buttocks hurt as if being pricked by needles. Old Cheng’s palm wasn’t something just anyone could endure.

Seeing Yun Ye rubbing his buttocks, Cheng Chumo’s face was full of sympathy. It seemed he himself hadn’t been spared these slaps either. “Let’s go together. Now if I don’t bathe for a day, I feel uncomfortable all over. Strange—before in the capital, my mother would force me to bathe with a feather duster, but now no one’s forcing me and I feel uncomfortable not bathing. What’s the principle behind this? Am I like a cheap-skinned donkey that won’t move without being beaten and backs up when whipped?”

“This is a matter of habit. A person can form a habit in fifteen days. Don’t believe it? Find a pig, and before feeding it every day, tap the pig trough once. After ten-some days, even if you don’t feed it, as long as you tap the trough, the pig will run over.”

“This is truly miraculous! If I tap your rice bowl, will you run toward me when you hear the sound after ten-some days?”

The two brothers went to the rear tent to bathe, arms around each other’s shoulders, which need not be mentioned. General Cheng sat in the main tent, waiting left but seeing no one, waiting right but seeing no one. He muttered in his heart—could it be that young fellow truly has talent and learning? He himself didn’t go to examine him in person, wanting to preserve some face for Yun Ye. Who would have thought this boy could face off against Huang Zhien for so long? Formidable!

Huang Zhien could be considered among the outstanding mathematics scholars in the capital. To solve the army’s logistics problems, he had swallowed his pride and sought out Liu Xin several times. That old codger even gave him attitude. Unable to bear the importuning any longer, he finally dispatched Huang Zhien to help him. Huang Zhien didn’t disappoint his reputation for talent—the army’s logistics became much smoother. Now Young Master Yun could compete with him until now without falling behind. Not easy! This old man misjudged him. A fourteen-year-old child could already compete with a forty-year-old middle-aged man and not fall behind. What kind of prodigy would he become when grown?

Thinking this, Old Cheng could no longer sit still. He stood up and walked toward the sleeping tent. From afar he saw a crowd of people surrounding the tent entrance, yet silent as death. The soldiers saw the general arriving and scattered with a roar.

He only saw Huang Zhien prostrate on the ground, muttering under his breath, writing and drawing with his hands, covered in dust as if fallen into demonic obsession. But Yun Ye’s figure was nowhere to be seen.

Old Cheng’s curiosity grew greatly. He raised his hand and beckoned over the guard protecting the sleeping tent, asking what had happened and where Yun Ye had gone.

That guard had also been to the salt mine with Cheng Chumo, witnessed the marvel of salt extraction, and heard the Monkey King tales. He had long admired Yun Ye with complete devotion and had been waiting for the general to ask him. His face full of disdain, he recounted from beginning to end how Yun Ye had driven Huang Zhien into demonic obsession with just a few words.

Old Cheng glanced at Huang Zhien, still calculating ceaselessly on the ground, and instructed the guard to bring him an umbrella for shade and prepare a pot of tea water for backup. Then he turned and returned to the command tent. As soon as he entered the command tent, a burst of extremely delighted laughter transmitted out from the great tent.