Chapter 20
Chapter 20
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Translator: Ace
Chapter: 20
Chapter Title: The Flashing Sign
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Yoo Seo-ha's eyes wavered.
Dozens of pairs of eyes fixed on him.
Everyone was waiting for his mouth to open.
This was the first time in his life he'd been the center of attention in front of so many people.
'I... I have to answer first. Just like the professor proved it...'
It was only the first day.
Yoo Seo-ha wanted to show respect.
So he decided to honor the professor's method.
Yoo Seo-ha quickly scanned the blackboard with his eyes.
A massive board pieced together from four panels, crammed full of an enormous volume of equations.
'Diophantine equations.'
It was one of his favorite fields.
Around the 3rd century, the Alexandrian mathematician Diophantus systematically explored various equations with integer solutions in his book Arithmetica.
Forgotten for a time when Alexandria burned, these formulas were revived by modern mathematicians like Fermat, Euler, and Gauss.
Yoo Seo-ha's eyes began devouring the equations at an astonishing speed.
Starting from the definition in the upper left of the first board.
His brain reacted instantly. He applied the basic form of the linear Diophantine equation, using the Bézout identity.
Extended Euclidean algorithm.
His brain reconstructed the algorithm in a flash. It simulated the entire inverse calculation in one go.
Second board.
More complex forms unfolded.
Integers expressed as the sum of two squares. Fermat's theorem on sums of two squares expanded in his mind.
His gaze drifted lower.
Fermat's Last Theorem and Euler's method of infinite descent applied in his head, verifying the equations in an instant.
He spotted Professor Park's expansions.
Applying Jacobi's triple product identity...
This had all taken just a few seconds.
'Huh?'
The smooth flow of equations hit a wall and ground to a halt.
Yoo Seo-ha's eyes stopped.
Something was wrong.
Near the top of the third board, midway through a complex expansion.
The sign was incorrect.
It should be minus, not plus.
In Euler's partition function expansion using the pentagonal number theorem, flipping the sign made the formula hold.
Thump.
As Yoo Seo-ha stared blankly at the board, the professor gave him a moment.
Yoo Seo-ha was the sole perfect scorer on the second exam. Young as he was, the professor believed he could keep up.
"Alright! Yoo Seo-ha, why don't you come up and explain?"
'Is he too nervous? Hope it's not presentation anxiety... that'd be trouble.'
Professor Park had seen this many times before.
Presentations were mandatory for math majors, not optional.
He thought he should help the boy gain experience.
Thump.
Yoo Seo-ha's heart pounded fiercely.
There was pressure from having to step in front of everyone. But more than that, the error on the board tormented him relentlessly.
The equations that followed seemed fine, suggesting it was just a simple notation slip by the professor. That made it even more irritating.
'Is it okay to point this out?'
Yoo Seo-ha's parents had always feared their exceptionally gifted son might grow into a flawed person. From childhood, they'd drilled into him excessive respect, consideration, and deference toward others.
Lacking experience, Yoo Seo-ha wasn't sure if a student was allowed to correct a professor's formula.
And then, the symptoms he'd kept suppressed until now erupted violently, triggered by the combination of it all.
Thump thump.
"...Yes."
Yoo Seo-ha stood from his seat.
His legs trembled.
Even as he pondered how to present, that wrong sign on the third board blinked repeatedly in his mind like a broken neon sign.
'It should be minus.'
One step, then another, toward the podium.
But with each step, his breathing quickened.
'I want to fix the equation.'
His fingers moved unconsciously.
His right index finger repeatedly traced in the air, changing the plus to a minus.
His chest tightened, cold sweat trickling down his back.
Atop the podium, he saw even more students' faces.
Expectation, curiosity, concern, mockery, pity.
A range of emotions flickered across them.
"Alright, shall we get started?"
Professor Park smiled encouragingly and handed him the chalk.
Yoo Seo-ha took it with trembling hands.
Blink.
Blink.
The sign kept blinking.
"The basic approach to Diophantine equations is..."
He began speaking.
He tried to start with the first board, but his gaze kept drifting to the error.
Beep boop beep—
Now he was even hearing phantom sounds.
He couldn't take it anymore.
His face drained of color.
The students sensed something off with Yoo Seo-ha.
"What's wrong with him?"
"Is he sick or something?"
"Poor guy. Must be too nervous."
Whispers rippled through the room.
The professor shook his head.
Thinking it was too much for today, he was about to send him back and reschedule—when Yoo Seo-ha moved.
Step. Step.
He'd looked like he was in a panic, but suddenly he lifted his head and strode straight to the third board without hesitation. He went up on tiptoes to fix the writing.
But it was too high; he couldn't reach.
A somewhat comical sight.
Yet no one laughed at the bizarre scene.
"Yoo Seo-ha, what are you trying to do right now?"
The professor asked cautiously.
"I have to... fix the sign."
Professor Park furrowed his brow.
He stared intently at the third board.
Spotting a single symbol error amid the tangled equations was no easy task.
But since Yoo Seo-ha was trying to erase something, he zeroed in quickly.
"Ah..."
A sigh escaped Professor Park's lips.
Embarrassment flashed across his face.
The sign really was wrong.
"You're right, Seo-ha."
Professor Park muttered as he rubbed the sign with his finger, changing it from plus to minus.
Yoo Seo-ha's actions ceased.
The neon sign went dark.
Huuuuh—
Yoo Seo-ha let out a long sigh of relief.
The tightness in his chest vanished, his breathing returning to normal.
Yoo Seo-ha smiled brightly.
Professor Park felt an indescribable emotion watching him.
"Thank you, Yoo Seo-ha. That was a sharp catch."
Even professors were human; they occasionally botched signs or numbers when scribbling while lost in thought.
Yoo Seo-ha bowed his head.
Professor Park was an experienced scholar. He knew that history was full of eccentric geniuses among great mathematicians.
The classroom fell silent.
The students were stunned speechless.
Professor Park turned to face them, his expression hardening instantly.
"You all took faithful notes, but not one of you spotted the error. Were you just mindlessly copying without thinking?"
Disappointment crossed Professor Park's face.
He'd expected better from the nation's top selected geniuses.
J Ji-hoon clenched his fist.
His pride stung.
Go Chang-seok adjusted his glasses and flipped through his notes.
Shame was evident on his face.
Soo-jung accepted the situation as if it were only natural, staying silent.
"And Seo-ha."
"Yes."
"You hesitated earlier? Feel free to point out things like this anytime."
"We're teacher and student on the surface, but at heart, we're fellow travelers on the vast road of mathematics. Math doesn't advance without exchanging ideas. If you have a doubt, speak up regardless of age or status. Got it?"
"Yes! Professor."
Yoo Seo-ha nodded eagerly, beaming.
Professor Park watched with a pleased smile.
Yoo Seo-ha returned to his seat, and class resumed.
Free of his burden, Yoo Seo-ha exchanged thoughts on the proof with the professor. He came to understand why Professor Park had taken that approach.
"Analytic number theory is still too advanced for high schoolers."
Though unintentional, Professor Park's words stung the students.
Everyone snapped to attention, unable to accept it. The class buzzed with energy. Professor Park was thrilled by the atmosphere.
But the students thought differently.
'Yoo Seo-ha gets it, but we don't?'
'I've studied advanced number theory. Was he dumbing it down because he thought we couldn't handle it?'
No one had ever treated them this way before.
"Ji-hoon, you get this theorem, but the others don't. Don't get too far ahead."
It was the same old line they'd always heard.
Wherever they went, they were special—but here, they needed to hold back.
The students felt humiliated.
Stung by Yoo Seo-ha, Ji-hoon shot to his feet.
"I've heard there's a way to solve Diophantine equations using continued fractions?"
Go Chang-seok jumped in right after.
"Finding Pythagorean triples is a Diophantine equation too, right? Is there a general formula?"
The classroom heated up.
Flames of competition ignited in the students' eyes. They vied to ask deeper, sharper questions like Yoo Seo-ha to earn favor.
Professor Park grinned ear to ear, darting between boards as he answered enthusiastically.
From day one, Yoo Seo-ha had poured catalyst onto these top geniuses' competitive spirits, awakening their dormant potential.
But Soo-jung knew Yoo Seo-ha better than anyone else there.
'No matter what you guys do...'
Soo-jung snorted inwardly.
She planned to stick to her reliable second-place strategy.
'How could you beat that guy?'
Even what he'd shown today wasn't his true self. She had no clue where the bottom of his ability lay.
Time flew, and class was nearing its end.
Professor Park checked his watch and smiled.
"Our first class today was truly lively. I can feel your passion."
The students nodded, relieved.
"To avoid ending on a dull note, let me make a fun proposal before we wrap up."
Professor Park wiped the board clean and wrote a new problem.
[Find the maximum product of natural numbers that sum to 2077.]
"I'll give a privilege to whoever solves this quickly."
Everyone stared at the problem tensely.
In winter school, even minor privileges mattered if they tied to selections—they had to grab them.
"First half to finish get to choose their roommates."
Murmurs rippled.
The students' eyes widened.
Choosing a roommate for two weeks of shared living was huge.
There was no rest here.
Even in the dorm, everyone would study. They all knew roommates were the top factor shaping study conditions.
Snoring was the least of it.
Body odor from skipping showers or muttering to oneself would be disastrous.
Students began glancing around slyly.
Ji-hoon's gaze lingered on one student who was biting nails and leaving them on the desk.
'Ugh! Gotta avoid that one.'
Everyone pondered who to pick, thinking alike.
But they weren't seasoned high school seniors.
They slammed their heads into their notes, attacking the problem furiously.
'Shoot!'
Ji-hoon and Soo-jung started on it too.
"Alright, let's begin."
The professor scanned the room.
Maximum product of natural numbers summing to 2077.
Trickier than it seemed, but with the right approach, solvable in 30 minutes.
Students dove in with their own methods.
Not Yoo Seo-ha, though.
He stared blankly ahead, then signaled toward himself.
He timidly raised his hand and spoke shyly.
"Um... Professor. I solved it. Can I pick my roommate now?"
Silence fell.
Even the students who'd maintained composure throughout class couldn't help dropping their pens this time.