Ding-dong-deng—
The bell signaling the end of the exam rang.
Seo-eun set down the pencil she had been drawing with and stretched. The student beside her was clutching his answer sheet, correcting something.
“You there! Put your pencil down!”
The proctor shouted in a sharp voice.
“Shouldn’t that be marked as a zero?”
“Seriously. Does he think the rest of us finished early because we had time to spare?”
Several students made their displeasure obvious, but Seo-eun did not even glance their way.
In the world of mathematics, competition with others is not particularly important.
How fast one solves a problem, even whether one gets the correct answer, are all secondary matters.
For Seo-eun, the only values that mattered were why a single line of an equation flowed the way it did, and what kind of world that definition created.
Her brother had never once praised her simply for getting an answer right. But when she properly grasped the essence of a problem, he looked more delighted than anyone. Seo-eun truly loved seeing that expression on his face.
“Everyone, good work. Please gather your belongings and leave quietly.”
The proctor’s gaze lingered on Seo-eun for a moment.
As a teacher at Seoha’s alma mater, he was a believer in the doctrine that genes explained all things. And Seo-eun, with her perfect score on the first exam, had added firm conviction to that belief.
‘She really does enjoy solving problems.’
In this respect, she resembled her brother. That mindset of not caring at all about the eyes of those around her, too.
Seoha had been so outstanding that there had been little pleasure in teaching him, but from what the proctor had observed, she was not quite at that level. She hesitated at points where she was stuck, and the moment she understood, she overturned her equations without hesitation.
‘This will be interesting.’
Despite her young age, she was superior to any of the gifted students gathered from across the country.
A faint smile spread across his lips.
“It’s snowing a lot.”
Seo-eun came out of the building and looked up at the sky.
When she opened her phone, there was a message from her brother.
—I’m at a study café nearby. I’ll send you the map, so come straight over when you’re done!
Seo-eun tilted her head, then began walking toward the school gate. The café was only five minutes from the testing site.
Seo-eun arrived there in three minutes. But—
“Huh?”
The front of the café was swarming with people.
There were students in gifted high school uniforms, university students wearing department jackets, and even two cameras with broadcasting station logos on them.
Someone who looked like a reporter asked the person beside him.
“They still can’t get in?”
“No, they say there are no seats inside. Even when they ask them to move, they won’t listen.”
It was below freezing and snowing besides, yet no one was leaving.
‘Don’t tell me something happened to Oppa?’
Her heart grew anxious.
She stood on tiptoe and tried to look inside, but the wall of people blocked her, and it was no use.
“Excuse me. Just a moment!”
She tried to squeeze through the gaps, but it was impossible. While Seo-eun was hopping up and down, struggling, the closed glass door opened.
Warm air leaked out through the crack. The crowd stirred and turned their gazes all at once.
A tall, handsome man with orange hair.
Even among the crowd, Theo stood out conspicuously.
“Theo!”
He swept his eyes over the crowd once, then found Seo-eun immediately.
Most of the people here were connected to mathematics in one way or another. They recognized Theo’s face. A few naturally stepped aside to make a path.
“Is Oppa okay?”
Seo-eun asked in an urgent voice.
“Let’s go inside first.”
Seo-eun trotted after Theo as he led the way.
* * *
Not long after he began writing the equations, Seoha regretted it.
Because this was not a theorem that could be finished in a few hours. As the formulas progressed, the auxiliary lemmas and prerequisite conditions that needed to be resolved came spilling out one after another.
Uncountable cardinal theory, measure theory, homological algebra, the functor structures of category theory, invariants of topological isomorphisms, and even the task of redefining computational complexity theory through Yu-Riemannian geometry.
Touch one thing, and ten others trembled. If he were to prove it properly, there was no telling how many days it would take.
Seoha could not hide his anxious expression.
‘Seo-eun will be here soon.’
Ducky seemed to be thinking the same thing, and the two soon reached an agreement.
‘Good! Let’s skip ahead!’
Mathematicians have two ways of writing.
An explanation considerate of the reader, or a proof meant only for oneself. Since he was not going to show it to anyone anyway, choosing the latter would not be a major problem.
‘What is this?’
Chanseong, KAIST’s youngest professor of mathematics, felt his eyes spin.
It had been difficult, but he had definitely been following. Yet suddenly, the equations went berserk. A section that would normally require an entire paper was being omitted wholesale.
And not just once, but over a dozen times.
Surely this flow had been written backward after first seeing the result. But no matter how hard he tried, he could not see it.
It seemed he was not the only one thinking so, as murmurs spread around him.
“Please move aside for a moment.”
Theo’s voice.
Seo-eun was worried that something might have happened to her brother.
Rattle.
When the door opened, the scene inside finally came into view. She stopped dead where she stood.
“…Huh?”
The strong smell of markers.
Walls covered in white paper, and equations filling them completely.
It felt as if her breath had stopped. Numbers and symbols continued densely up near the ceiling.
It was as though the wall were alive. Equations branched out in many directions, unbroken, reaching somewhere like rivers flowing toward the sea.
The café was packed with people, but Seoha seemed not to notice, focusing only on the equations.
Theo spoke in a low voice, as if warning her.
“Don’t be surprised. Right now, Seoha might be a little different from the oppa you know. It’s like a switch he flips to concentrate when he’s solving a difficult problem…”
She did not hear him.
Seo-eun smiled brightly as she looked at Seoha.
His expressionless face, his disheveled hair, the marker stains on the ends of his rolled-up sleeves.
‘What? I was worried for nothing.’
Concentration mode.
Although her brother was endlessly kind in everyday life, Seo-eun, who had been with Seoha ever since she was born, knew that he sometimes showed another face.
‘He pretends it’s nothing because he’s embarrassed, though.’
A bashful laugh slipped out.
At times like that, her brother became quiet and wore a slightly uncomfortable expression.
Seo-eun quietly sat down in a chair and waited for him to finish everything.
Ssssk.
The logic became extremely complex.
A Turing machine is, in essence, governed by time. The act of moving along a tape one cell at a time and changing states. In other words, the order of operations is the premise that takes precedence over all else.
But in the world Seoha had established, the universe did not process problems sequentially. It was a world where the entire structure of a problem existed as a single topological figure. There, the answer constantly changed and came to exist in the most natural state of equilibrium.
‘The simultaneity of uncountable space.’
It was a new concept that surpassed the limits of existing computation theory.
Seoha thought of Turing.
A lonely boy who had wept after losing his friend in childhood. Having no communion with others, he must not have known how to fill that loss.
Seoha gently spoke to that lonely genius.
‘How is it? Have you met your friend there?’
He truly understood Turing.
What Turing had wanted to create was not a friend, but a world in which he would not have had to lose him. It was a memorial carried out in the most desperately painful way throughout his entire life.
But through the help of many people, Seoha had come to realize.
‘Alan, relationships are singular things. They are precious because they can be lost. I hope you and your friend are happy there.’
「Q.E.D.」
The marker placed the final point.
Seoha drew his hand away and trembled faintly. Seo-eun could not understand what was written on the wall, but she could feel the sense of liberation in his back.
“Oppa!”
This, too, was a side of her brother Seo-eun truly loved. No matter how serious his face was, whenever she called him, he always smiled brightly.
Seoha turned around.
The nerves that had been pulled taut loosened, and warmth seeped into his face. Seoha smiled radiantly. Seo-eun shrugged her shoulders at Theo as if to say, See?
“Did the exam go well?”
“Yeah!”
“Then let’s go home.”
“Okay. Mom said she’d make lots of delicious food.”
Seoha picked up his coat.
The mathematicians who had come to the café were on the verge of going mad with frustration. They desperately wanted someone to explain it, but the person in question showed no intention of doing so.
Sensing the atmosphere, Mathholic bravely approached Seoha and asked.
“Um… Director Yu! What meaning does the theorem you wrote on the wall have?”
Everyone’s gaze focused on one spot.
Seoha looked troubled. It had only been a very private proof, but it seemed it was already too late to gloss over it.
He sighed, then answered.
“It means that Turing’s computational complexity theory was unable to encompass the entirety of the universe.”
Murmur, murmur—
Unable to overcome his impatience, Chanseong abruptly stepped in between them.
“Director! This proof is unlike you. It isn’t a theorem in complete form. Here, and here! Why are there so many leaps in logic?”
Seoha scratched his head in embarrassment.
“It was almost time for my sister to arrive. I just wanted to quickly confirm the answer.”
Just to meet his sister?
The surroundings fell silent. Sighs broke out here and there.
Chanseong and Junil’s mouths fell open.
Seoha put on his coat and carried Seo-eun’s bag for her. He was about to leave the café with the Apex team members.
“Wait!”
Chanseong called out to him in an urgent voice.
“Surely you’re not just going to leave like this? Please, at least explain this part…”
Seoha shook his head.
“I’ll write it properly someday and publish it as a paper.”
“Someday… you say?”
His words did not reach him.
The glass door closed, and Seoha’s figure disappeared into the snow.
Chanseong stared up at the wall with a hollow expression.
In the café Seoha had left behind, someone said with gleaming eyes.
“Let’s take pictures.”
Click!
Click!
People took out their phones all at once. The sound of shutters poured down like rain. One of them lightly touched the corner of a sheet of paper with his hand.
“This is attached with tape, isn’t it? If we peel it off carefully…”
“Huh? Me too, me too!”
“Could I take one sheet as a memento as well?”
“No matter how I look at it, these two sheets seem like a set. Wouldn’t it be better for one person to take them?”
“What are you talking about? Obviously, the university should take them!”
When Seoha and his team left without claiming ownership, the inside of the café instantly turned into pandemonium.
Chanseong clutched his head with both hands.
“Everyone! Please stop!”
“You be quiet. Don’t think about taking them to the university!”
Documents whose value no one could predict if preserved. Even those who had not had much interest in mathematics joined in, and the uproar grew louder.
Watching this, Woohyeon frowned.
“Stop!”
At his shout, like a lion’s roar, the café instantly fell silent.
His relationship with Seoha was a well-known fact.
People assumed Woohyeon would take all of it. However, the words that came from his mouth were entirely different.
“Just leave them here. If you need to study them, come here and look.”
“R-Really? Is that all right?”
A windfall he had not even expected.
The café owner’s eyes grew wide.
“Yes, that would be best. You provided the place, after all.”
Everything Seoha had written would soon become history.
From the beginning, Woohyeon had never intended to take it down. Leaving it intact in its original form would be best for everyone.
He handed the owner his business card.
“If it becomes difficult to manage, contact me anytime. I’ll help with preservation treatment.”
The surrounding gazes were full of envy.
The owner accepted the business card with both hands.
“Thank you. Thank you so much.”
He looked up at the wall.
It had been more than ten years since he opened the café. His income had been meager, and his only joy had been the small sense of fulfillment he felt watching students study.
He bowed his head to Woohyeon for a long time.
Now his café would become famous as a local landmark. At least enough that he would no longer need to worry about making a living.
* * *
Three days later.
The owner, who had come to work at the café, rubbed his eyes, wondering if he was seeing things.
A line had formed in front of the shop.
People dragging suitcases as if they had come straight from the airport.
“Can I come in?”
He flinched at the sudden sound of English.
As though they knew one another, they exchanged light greetings. Their skin colors and languages were all different. Yet every single one of them was looking at the same place.