As soon as they arrived home, Uhyeon exchanged a few brief words with Miyeong before setting up the chessboard.
Seoha never let go of the textbook in his hands.
“Shall I explain the basic rules first?”
“No. I understand them more or less.”
Seoha closed the book and sat down.
‘Chess resembles probability theory.’
Each move had a winning probability assigned to it.
Just as with Bayes’ theorem, one could observe an opponent’s previous moves and estimate the probability distribution of their next move.
A clear 8 x 8 chessboard appeared in Seoha’s mind. He simulated the paths along which each piece could move.
“Then let’s begin.”
Uhyeon pushed the pawn in front of his queen forward two squares.
‘1. d4, a Queen’s Gambit line.’
The probability calculations began.
‘Since it’s the first game, I’ll go with the highest-probability move: 1...d5.’
The expected win rate of Seoha’s first move was 44.2%.
Uhyeon gave him a peculiar smile and immediately made his next move.
Click.
Click.
Click.
The pieces on both sides began to intertwine in a complex web.
‘Hmm?’
Seoha’s brows rose.
Instead of making the move with the highest expected win rate, Uhyeon played f5.
The Classical Dutch.
The variations that could arise from here were nearly infinite.
Seoha defended by assigning priorities, but even when he won the individual battles, the pieces had somehow ended up in disadvantageous positions when viewed from the broader flow of the game. Like clothes getting wet in a light drizzle, the losses accumulated before he knew it.
Uhyeon made his final move.
“Checkmate.”
“I lost. Next game.”
Seoha gained an insight.
‘A human can’t calculate every probability in chess.
I need to make my opponent play according to my intentions and narrow down the possible variations. Then I can calculate the winning probability in my head from beginning to end.’
Click.
Click.
Uhyeon, who had easily won the first game, had grown serious before he knew it.
The time it took him to deliver checkmate grew longer and longer.
They had played only five games, yet he could no longer end them easily.
‘It’s getting harder and harder to win.’
Cold sweat ran down his back.
No one looking at Seoha now would have thought he was merely a novice who had learned chess that very day.
Seoha entered a state of complete concentration.
The Smith–Morra Gambit.
The pace of the game accelerated sharply.
‘The teacher’s move selection didn’t follow a uniform distribution, which is what confused me. But the sample size is growing. Focus on restricting the pawns’ movement so they can’t run rampant.’
“Have some of this while you play.”
Miyeong brought over iced instant coffee, ice cubes bobbing on top.
But neither of them heard her.
A knight moved at the tips of Seoha’s fingers.
Click.
‘From Nc6 to Ne5. Seize the center while simultaneously blocking the teacher’s bishop line.’
Uhyeon flinched. He had considered about five moves Seoha might make, but this was not one of them.
‘As expected, the teacher is also stronger when his opponent plays predictable moves. But when the pattern breaks, his calculation time grows longer. If I make unexpected moves and force the game into a battle of calculation, I can win.’
Uhyeon thought that this might be the only chance he would ever have to beat Seoha at chess again.
No matter how brilliant Seoha’s mind was, this was something his pride could not accept.
‘Still, not on his first day.’
Click.
Uhyeon forced an exchange.
Of course, it put him at a disadvantage. But this was surely a move Seoha had not included in his calculations.
Seoha flinched.
As expected, he seemed momentarily confused, but then accepted the exchange.
‘That was childish.’
Uhyeon gave a bitter smile.
A teacher overturning the board simply because he did not want to lose.
Even so, this too was an undeniable part of chess. Seoha could learn that such strategies existed as well.
Uhyeon gave up on victory and began aiming for a draw.
Click.
Perhaps sensing something strange, Seoha retreated his bishop. It was an uncharacteristically passive move.
‘Yes, just as I thought.’
Fifteen years of experience did not vanish into thin air.
Even against a genius, fifteen years were enough to hold on to the hem of his pants for at least one day.
The conservative defense continued.
At this rate, even if he had somewhat fewer pieces, a point would certainly come when neither side could finish the other off.
But on the fifteenth move—
Click.
Seoha’s queen suddenly leaped into the center.
“Huh?”
‘Ah, damn...’
By the time he realized it, it was already too late. Seoha’s defensive moves over the past several turns had actually been intended to secure a covert route for his queen’s entry.
At some point, he had changed his strategy.
Uhyeon muttered under his breath.
“A draw trap.”
It was a reverse-psychology strategy used when an opponent was aiming for a draw.
Seoha’s queen began threatening Uhyeon’s king, and tension spread across the chessboard.
Trying to seize the key routes in pursuit of a draw had been a mistake.
“Qd5+.”
Seoha’s voice was calm.
Uhyeon moved his king out of danger, but the catastrophe was already set in motion.
From this point onward, there was only one path.
There was no way to evade Seoha’s forced sequence.
Click.
Click.
“Checkmate.”
Silence descended.
Uhyeon stared blankly at the chessboard.
“This is ridiculous. Even if I wasn’t playing at my best...”
Uhyeon’s body trembled at the unreasonable result.
“Then shall we play another game?”
Seoha’s eyes sparkled.
“Let’s stop for today. We’ll play next time when I’m in perfect condition.”
But Uhyeon was certain.
The day when he could win again would probably never come.
The light in Seoha’s shining eyes seemed far too dazzling to him.
* * *
On Saturday afternoon, Seoha was in his room reading a chess textbook.
Winter in Okcheon was cold enough to chill one’s bones.
He sat on the warm floor, covered himself with a blanket, and read his book, occasionally helping his younger sister with her drawings.
“Want some tangerines?”
Miyeong, who had been watching the two of them fondly, rummaged through the cupboard.
“Yes!”
“Yes.”
The son and daughter nodded together amiably.
As Seoha cleared a space on the table for the tangerines, he heard someone calling for him from outside.
“Seoha—”
‘Is there anyone who would come looking for me?’
Miyeong stopped what she was doing and looked outside.
“Seoha! It must be a friend!”
‘A friend?’
When he was younger, neighborhood friends would sometimes come looking for him to play soccer, but not these days.
The front gate opened, and a familiar voice drifted in.
“Hello. My name is Kim Junsik, and I’m in the same class as Seoha.”
His gestures and voice were timid.
“Oh my! Come on in.”
Miyeong’s expression brightened, apparently happy that a friend had come to see her son.
But Seoha’s mind was filled with questions.
‘What’s going on? I’ve never even spoken to him before.’
Then Seoha’s gaze fell on Junsik’s hands. He had brought a workbook.
“I’ll bring you something to drink. Can you wait just a little?”
“Ah... yes. Thank you.”
Once Junsik sat down in the living room, an awkward silence fell. Seoeun, apparently shy around strangers as well, had slipped behind her brother and was peeking out at him.
Seoha was curious about why Junsik had come, but he waited without pressing him.
“Um...”
Junsik had come all this way, but now he did not know how to begin.
Junsik had transferred to Dodam Elementary a month ago. He had done so because he had heard that the school had a teacher who was exceptionally good at teaching mathematics.
But the lessons he had been looking forward to were all basic material he already knew.
Even when he said he wanted to study something more difficult, the teacher only shook his head.
“You’re still lacking in the fundamentals, so you can’t yet.”
The teacher’s words had angered him.
“Then what about Seoha? Why does he get to leave every day without doing remedial work like the rest of us?”
Seoha was a fifth-grader who had placed first nationwide in a mathematics competition.
His mother had urged him to become friendly with that boy if possible. But despite being in the same class, he had never had the chance to say even a word to him. Seoha was always talking with other children, and as soon as school ended, he went straight home.
Until now, Junsik had been the smartest child in Geumsan.
Every teacher praised him, and he was always the envy of the children around him.... The teacher who had come from Seoul had even told him that he would do more than well enough if he went to Gangnam’s famous school district.
But here, everything had returned to the beginning.
“Hmm... Seoha is a little different. You’re an incredibly smart child, Junsik. So you must never compare yourself to Seoha, all right?”
The teacher had gently admonished him despite his own curt question.
Rather than reassuring Junsik, the sight had twisted something inside him.
Seoha was always the center of the children’s conversations here.
“No way! My dad says Seoha is going to America!”
“I heard that’s not true. I heard he’s going straight to college.”
“Who’s going to help us with our homework when we get to middle school? We never had to worry when Seoha was around.”
Yoo Seoha was always quiet.
He never showed off or treated his friends differently.
Junsik had realized within a few days of transferring that most of the girls in the class liked Seoha.
‘First place in the national competition?’
‘If I entered, I’m confident I could place too.’
Junsik felt the need to prove himself. So he spent all of yesterday searching through the workbooks at home for the most difficult problem he could find.
All he needed now was courage!
His body shrank back when he saw Seoha, but Junsik bravely opened his mouth.
“I heard you’re good at math.”
“Huh?”
Seoha flinched as though Junsik’s words had caught him off guard.
“I brought a problem...”
Junsik awkwardly opened the workbook.
Just then, the little girl hiding behind him happily sprang out.
“Wow! Do you like numbers too, big brother?”
All of a sudden?
The situation was entirely different from what he had imagined, and Junsik’s mind froze. But he soon grasped what was happening.
“Uh... yeah. I like them.”
“Wow! Then play with me. A number game!”
Play with a five-year-old? But seeing her expectant expression softened his heart.
‘I’ll play with her quickly and then leave. Besides, when it comes to numbers, I’m confident.’
“Sure. What are we going to do?”
“Number chain!”
The five-year-old Seoeun had a proud look on her face.
Even Junsik thought she was adorable.
The troubled look on Seoha’s face brightened.
“Then let’s play together.”
At Seoha’s words, Junsik hurriedly asked,
“W-wait. What’s a number chain?”
“We say prime numbers. We used to play this when we were little. You just say them in order, starting from the smallest.”
“Yeah! I beat Mom and Dad every time. I can’t beat Big Brother or Sujeong, though, and the kids at kindergarten won’t play with me.”
Apparently, unlike their parents, Seoha did not go easy on his little sister.
Junsik nodded.
“Oh! If that’s all it is, no problem. Let’s start.”
And so the game began.
“2.”
“Three!”
“5.”
“7.”
He thought it would end quickly, but it was not easy. Before long, the numbers had passed 100.
“101.”
“One hundred three!”
“...107.”
He was a little late.
Sweat trickled down Junsik’s back.
Before long, the numbers passed 200.
“227.”
“Two hundred twenty-nine!”
Junsik’s face brightened.
The little girl had made a mistake.
“Huh? Isn’t that not a prime number?”
“Hehe. I won!”
As if she could not hear him, Seoeun stood up and performed a strange, wobbling dance.
It oddly grated on his nerves.
“That is a prime number. Check your calculations carefully.”
He divided it and found that it was prime.
Junsik’s face reddened with embarrassment.
“L-let’s do it again!”
The hellish number chain continued from where they had gone wrong.
Every loss belonged to Junsik.
At first, he thought they had been simple mistakes, but he continued to be the only one who got things wrong.
Junsik’s voice grew quieter and quieter.
He had clearly come here to challenge Seoha to a battle of problems.
“439.”
“Four hundred forty-three!”
It was Junsik’s turn. His mind went blank.
‘467? 469? 471?’
Various numbers whirled around in his head.
“F-four hundred...”
The words would not come out.
It felt as though his throat were blocked.
“What’s wrong, big brother?”
Seoeun looked at Junsik with a puzzled expression.
Junsik’s eyes reddened.
“N-no, it’s nothing. I’m going home now.”
Junsik picked up his workbook and hurriedly stood. Before the drinks even arrived, he put on his shoes and ran outside as though fleeing.
“Huh? Seoha, where did your friend go?”
Miyeong had brought over a tray with cola and juice, and she asked while watching Junsik’s departing back.
“He left after playing with Seoeun.”
Seoha looked at his sister, who was grinning brightly as though she were pleased about something.
“What a nice boy.”
At Miyeong’s words, Seoha and Seoeun nodded at the same time.
After that day, Junsik never spoke to Seoha again.