Seoha’s eyes wavered.
Dozens of pairs of eyes were fixed on him.
Everyone was waiting for Seoha to open his mouth.
It was the first time in his life he had ever been the center of attention in front of so many people.
‘F-first, I need to answer. Following the method the professor proved…’
It was only the first day.
Seoha wanted to be polite.
So he decided to respect the professor’s method.
Seoha quickly scanned the blackboard with his eyes.
An enormous blackboard made by joining four boards together. A massive amount of formulas was densely written across it.
‘Diophantine equations.’
It was a field Seoha liked.
Around the third century, the Alexandrian mathematician Diophantus systematically dealt with various equations that had integer solutions in his work Arithmetica.
This formula, forgotten for a time after Alexandria burned, was revived by modern mathematicians such as Fermat, Euler, and Gauss.
Seoha’s eyes began reading the formulas at tremendous speed.
Starting from the definition at the upper left of the first blackboard.
His brain reacted at once. The basic form of a linear Diophantine equation, applying Bézout’s identity.
The extended Euclidean algorithm.
His brain reconstructed the algorithm in an instant. It even finished simulating the back-substitution process all at once.
The second blackboard.
More complex forms unfolded.
Integers expressed as the sum of two squares. Fermat’s theorem on sums of two squares developed in his mind.
His gaze moved farther down.
Fermat’s Last Theorem and Euler’s method of infinite descent were applied in his head in an instant, and he began verifying the formulas.
He saw the expansions Professor Park had used.
If Jacobi’s triple product identity was applied…
Only a few seconds had passed up to this point.
‘Huh?’
The formulas he had been reading smoothly came to an abrupt halt, as if they had hit a wall.
Seoha’s eyes stopped.
Something was wrong.
Near the top of the third blackboard, in the middle of a complicated expansion.
The sign was wrong.
It shouldn’t be plus. It should be minus.
In Euler’s expansion of the partition function using the pentagonal number theorem, the sign had to change for the formula to hold.
Thump.
When Seoha stared fixedly at the blackboard, the professor waited, giving him a moment.
Yu Seoha had been the only one to receive a perfect score on the second exam. He was young, but Professor Park believed he could follow this much well enough.
“All right! Shall Student Yu Seoha come up front and explain?”
‘Is he too nervous? It would be a problem if he has stage fright…’
Professor Park had seen many cases like this.
Presentations were not optional for a mathematician, but essential.
He thought he should help him gain experience.
Thump.
Seoha’s heart pounded violently.
There was also the pressure of having to stand in front of people. But more than that, the error on the board tormented him persistently.
Judging by the fact that there were no problems with the progression of the formulas after that, it was probably a simple notation mistake on the professor’s part. That made it bother him even more.
‘Is it okay to point this out?’
From the time he was young, Seoha’s parents had feared that their excessively outstanding son might grow into a twisted person. So they had emphasized courtesy, consideration, and respect toward others to an almost excessive degree.
Lacking experience, Seoha did not know whether it was permissible for a student to correct a professor’s formula.
And the symptom he had managed to suppress until now was triggered fiercely under the combined influence of all these things.
Thump, thump.
“…Yes.”
Seoha rose from his seat.
His legs were trembling.
Even as he thought about how he should present, the wrong sign on the third blackboard flashed repeatedly in his mind like a broken neon sign.
‘It has to be minus.’
Step by step, he moved toward the podium.
But the farther he walked, the more labored his breathing became.
‘I want to fix the formula.’
His fingers moved unconsciously.
His right index finger repeated the motion of changing a plus into a minus in midair.
His chest tightened, and cold sweat trickled down his back.
Once he stood on the podium, he could see even more students’ faces.
Expectation, curiosity, concern, ridicule, pity.
Various emotions appeared and disappeared on their faces.
“Now, shall we begin?”
Professor Park handed him the chalk with an encouraging smile.
Seoha accepted the chalk with a trembling hand.
Blink.
Blink.
The sign was still flashing.
“The basic approach to Diophantine equations is…”
He began to speak.
He tried to begin explaining while looking at the first blackboard, but his gaze kept turning toward the error.
Wee-oo, wee-oo—
Now he even seemed to be hearing hallucinations.
He couldn’t endure it any longer.
His face went pale.
The students sensed something was off with Seoha.
“What’s wrong with him?”
“Is he sick or something?”
“Poor guy. He must be too nervous.”
Whispers came from here and there.
The professor shook his head.
Thinking that today was too much and that they would have to try again later, he was just about to send him back when Seoha moved.
Step. Step.
Seoha, who had looked as though he were in a panic, suddenly lifted his head and walked without hesitation toward the third blackboard. Then he stood on tiptoe and tried to correct what was written on the board.
But it was too high; he couldn’t reach.
It was a somewhat comical sight.
But at this bizarre scene, no one could laugh.
“Yu Seoha, what are you trying to do right now?”
The professor carefully asked.
“The sign… I need to fix the sign.”
Professor Park narrowed his brow.
Then he stared at the third blackboard for a long while.
Finding the error of a single symbol among a tangle of complex formulas was by no means easy.
But since Seoha had been trying to erase something, he could identify it quickly.
“Ah…”
A sigh escaped Professor Park’s mouth.
A look of bewilderment flashed across his face.
The sign really was wrong.
“Seoha is right.”
Professor Park murmured, then lightly rubbed the sign with his finger and corrected it. From plus to minus.
Seoha’s movement stopped.
The neon sign went out.
Phew—
Seoha let out a long sigh of relief.
The tightness pressing down on his chest disappeared, and his breathing returned to normal as well.
Seoha smiled brightly.
Watching him, Professor Park felt an emotion he could not quite put into words.
“Thank you, Yu Seoha. That was a truly sharp observation.”
Professors were human too, so when writing formulas while thinking of something else, they sometimes got a sign or a number wrong.
Seoha bowed his head.
Professor Park was an experienced scholar. And he knew very well that throughout history, outstanding mathematicians had included all kinds of eccentrics.
The lecture hall was quiet.
The students were silently shocked.
Professor Park turned and looked at the students. Then his expression hardened at once.
“All of you took notes diligently, but none of you discovered the error. Were you simply copying things down without thinking at all?”
Disappointment flashed across Professor Park’s face.
He had expected that gifted students selected from across the country would be better than this.
Jihun clenched his fist tightly.
His pride was wounded.
Go Changseok adjusted his glasses and flipped through his notes.
Shame was clearly written across his face.
Sujeong simply accepted the situation in silence, as if it were only natural.
“And Seoha.”
“Yes.”
“You hesitated earlier, didn’t you? You may point out things like this at any time.
On the surface, we are teacher and students, but on a deeper level, we are also companions walking together along the vast path of mathematics. Without the exchange of ideas between us, mathematics cannot develop.
Rather, when you have a question, you must speak up regardless of age or position. Do you understand?”
“Yes! Professor.”
Seoha nodded repeatedly, looking happy.
Professor Park watched him with satisfaction.
Seoha returned to his seat, and class resumed.
Freed from the burden, Seoha exchanged opinions with the professor regarding the proof. Seoha came to understand why Professor Park had to use this approach.
“Analytic Number Theory is still far too early for high school students.”
Though he had not intended it, Professor Park’s words provoked the students.
As if refusing to lose, everyone began focusing on the class. The class grew lively. Professor Park was truly pleased with this atmosphere.
But the students thought differently.
‘So Yu Seoha can do it, but we can’t?’
‘I studied advanced number theory, though? He was explaining it simply because he thought we wouldn’t understand?’
No one in their lives had ever treated them this way.
“Jihun, you understand this theorem, but the other kids don’t. So let’s not get too far ahead.”
That was what they had always heard.
No matter where they went, they had been special. But here, they were the ones being accommodated.
The students were feeling humiliated.
Stimulated by Seoha, Jihun shot to his feet.
“I heard there’s also a way to solve Diophantine equations using continued fractions?”
Not to be outdone, Go Changseok cut in as well.
“Finding Pythagorean triples is also a Diophantine equation, right? Is there a general formula?”
The lecture hall heated up.
Flames of competition burned in the students’ eyes. Each of them tried to leave an impression by asking deeper and sharper questions, like Seoha had.
Professor Park, with his mouth stretched into a broad grin, roamed all over the blackboard, absorbed in answering them.
From the very first day, Seoha had poured in the catalyst called rivalry and awakened the potential sleeping within the nation’s top gifted students.
But Sujeong knew Seoha better than anyone else here.
‘No matter how hard you all try…’
Sujeong snorted.
She intended to stick to a firm second-place strategy.
‘How are we supposed to beat that?’
Even what he had shown today was probably not Yu Seoha’s true self. She had no idea of Seoha’s real level, not even where the bottom of it lay.
Time passed, and the lecture was about to end.
Professor Park checked the clock and smiled.
“It was our first class today, but it was truly lively. I can feel your passion.”
The students nodded with relieved expressions.
“It would be dull to just let you go, so before class ends, I’ll make one interesting proposal.”
Professor Park wiped the blackboard clean and wrote a new problem.
[Find the maximum value among the products of natural numbers whose sum is 2077.]
“I will grant a privilege to the students who solve this problem quickly.”
Everyone looked at the problem with tense expressions.
At winter school, even the smallest privilege had to be secured, since it was connected to selection.
“I’ll give the first half of you the right to choose your own roommates.”
A stir ran through the room.
The students’ eyes widened.
Choosing a roommate they would live with for two weeks was a very important matter.
There was no rest here.
Everyone would study even in their rooms. They all knew well that the roommate was the most important factor determining their study environment.
Snoring would be getting off easy.
It would be disastrous if someone smelled because they didn’t shower every day, or had a habit of muttering to themselves.
The students began glancing around.
Jihun’s gaze stopped on one student. He was biting his fingernails and placing them on the desk.
‘Ugh! I absolutely have to avoid him.’
Everyone had similar thoughts as they pondered whom to choose in their minds.
But the experienced third-year high school students were different.
They immediately buried their heads in their notebooks and attacked the problem fiercely.
‘Oh, right!’
Jihun and Sujeong also began looking at the problem.
“All right, shall we begin?”
The professor looked around at the students.
The maximum product of natural numbers whose sum was 2077.
It could be trickier than expected, but if they found the proper approach, they should be able to solve it within thirty minutes.
The students began wrestling with the problem in their own ways.
But not Yu Seoha.
He stared blankly at the professor, sending him a signal with his eyes.
Then he cautiously raised his hand and shyly said,
“Um… Professor. I solved it. Should I choose my roommate now?”
Silence fell.
Even the students who had maintained their composure through constant effort all throughout class had no choice but to stop their pens this time.