Chapter 16
Chapter 16
-----------------------------------------------------------------
Translator: Ace
Chapter: 16
Chapter Title: Checkmate and Prime Number Game
-----------------------------------------------------------------
As soon as he got home, Woo-hyun had a brief chat with Mi-young and laid out the chessboard.
Seo-ha didn't let go of the manual.
"Shall I explain the basic rules first?"
"No. I get the gist."
Seo-ha closed the book and took his seat.
Chess is a lot like probability theory.
Each move comes with its own win rate.
Just like Bayes' Theorem, you can observe your opponent's previous moves and estimate the probability distribution of their next one.
An 8x8 chessboard materialized vividly in Seo-ha's mind. He began simulating the paths each piece could take.
"Then let's get started."
Woo-hyun advanced the pawn in front of his queen two squares.
1. d4, Queen's Gambit line.
The probability calculations kicked off.
Since it's the first game, the highest-probability response: 1. d5.
Seo-ha's expected win rate for his first move: 44.2%.
Woo-hyun flashed a peculiar smile and made his next move right away.
Tak.
Tak.
Tak.
Their pieces began tangling in complex patterns.
Hm?
Seo-ha's eyebrow arched.
Woo-hyun had played f5 instead of the move with the highest expected win rate.
Classic Dutch.
The variations branching from here were nearly infinite.
He focused on prioritizing defenses, but even if he won individual skirmishes, the bigger picture shifted—the pieces ended up in unfavorable positions. Losses accumulated like getting soaked in a drizzle.
Woo-hyun made his final move.
"Checkmate."
"I lost. Next game."
Seo-ha had gained enlightenment.
Humans can't calculate every probability in chess.
You have to maneuver the opponent into playing your intended moves, narrowing the possibilities. That way, you can track the win rate from start to finish in your head.
Tak.
Tak.
Woo-hyun's expression, triumphant after an easy first-game win, grew serious.
The time to deliver checkmate dragged on longer each game.
Just five games in, and he could no longer end them swiftly.
It's getting harder to win.
Cold sweat beaded on his brow.
No one watching Seo-ha now would guess he'd only learned chess today.
Seo-ha entered full concentration mode.
Smith-Morra Gambit.
The pace accelerated dramatically.
The teacher's move choices don't follow a uniform distribution—that's what threw me off. But samples are accumulating. Focus on restricting the pawns' mobility.
"Have some of this while you play."
Mi-young brought iced mixed coffee brimming with ice cubes.
But neither of them heard her.
The knight leaped from Seo-ha's fingertips.
Tak.
Nc6 to Ne5. Controls the center while blocking the teacher's bishop line.
Woo-hyun flinched. He'd anticipated about five moves Seo-ha might make, but this wasn't one of them.
The teacher excels when opponents play predictably. But stray from the pattern, and his calculation time stretches. Throw in an unexpected move and force a tactical slugfest—I can win.
Woo-hyun thought this might be his last chance ever to beat Seo-ha at chess.
Even for a genius like Seo-ha, it was unacceptable to his pride.
But it's only the first day, after all.
Tak.
Woo-hyun forced an exchange.
One that cost him, of course. But it was a move outside Seo-ha's calculations.
Seo-ha hesitated briefly, then accepted the trade.
Not very mature.
Woo-hyun gave a wry smile.
A teacher tempted to flip the board out of reluctance to lose.
Still, this was part of chess too—Seo-ha could learn that such strategies existed.
Woo-hyun abandoned victory and aimed for a draw.
Tak.
Sensing something off, Seo-ha retreated his bishop. An uncharacteristically passive move.
That's right, I knew you'd do that.
Fifteen years of experience didn't vanish.
No matter the genius, one day was enough to snag him by the pant leg.
The conservative defense continued.
Even if he was down material, a deadlock would eventually arrive.
But on move 15,
Tak.
Seo-ha's queen suddenly lunged into the center.
"Huh?"
Oh no...
Too late when he realized it. Seo-ha's prior defensive moves had secretly paved a path for his queen's infiltration.
He'd shifted strategy mid-game.
Woo-hyun muttered softly.
"Draw trap."
A reverse-psychology ploy used against draw-hunters.
Seo-ha's queen menaced Woo-hyun's king, tension rippling across the board.
Seizing key squares for a draw had been a blunder.
"Qd5+."
Seo-ha's calm voice.
Woo-hyun moved his king aside, but the endgame was set.
One-way street from here.
No escaping Seo-ha's pressure.
Tak.
Tak.
"Checkmate."
Silence fell.
Woo-hyun stared blankly at the board.
"Unbelievable. Even if I didn't go all out..."
His body trembled at the absurd outcome.
"Shall we do another?"
Seo-ha's eyes sparkled.
"Let's call it for today. Next time, full strength."
But Woo-hyun was certain.
He'd probably never beat him again.
Those shining eyes were too dazzling.
Saturday afternoon, Seo-ha was studying the chess manual in his room.
Okcheon's winter chilled to the bone.
Sitting by the warm floor heater, wrapped in a blanket, he read while occasionally checking his little sister's drawings.
"Want a tangerine?"
Mi-young rummaged through the cupboard, beaming at her harmonious kids.
"Yeah!"
"Sure."
Son and daughter nodded eagerly in unison.
As Seo-ha cleared space on the table for the fruit, a voice called from outside.
"Seo-ha—!"
Who's looking for me?
Mi-young paused and peered out.
"Seo-ha! Looks like a friend’s here!"
A friend?
He'd had neighborhood kids drop by for soccer when younger, but not lately.
The gate creaked open, followed by a familiar voice.
"Hello. I'm Kim Jun-sik, in the same class as Seo-ha."
Shy gestures and tone.
"Oh my! Come on in."
Thrilled her son had a visitor, Mi-young's face lit up.
But Seo-ha's mind swirled with questions.
What's this about? Never even talked to him.
His gaze landed on Jun-sik's hand—a workbook.
"I'll get you something to drink. Hang on a sec?"
"Ah... yes. Thank you."
Jun-sik sat in the living room, awkward silence settling in. Seo-eun, shy around strangers, peeked from behind her brother.
Seo-ha was curious but waited patiently without pressing.
"Um..."
Now that he was here, words failed him.
Jun-sik had transferred to Dodam Elementary a month ago, drawn by rumors of a great math teacher.
But the lessons were basic stuff everyone knew.
Even begging for harder material got him a headshake.
"Your basics aren't solid yet."
He'd fumed at that.
"What about Seo-ha? Why does he skip supplements and just go home?"
The fifth-grader who'd taken first in nationals.
His mom urged him to befriend the kid. But despite being classmates, no chance to chat. Seo-ha always talked with others and headed straight home after school.
Jun-sik had been Geumsan's smartest.
Praised by every teacher, envied by peers... The teacher from Seoul said he'd thrive even in Gangnam's elite districts.
Here, it was back to square one.
"Seo-ha's different. You're incredibly smart too, Jun-sik. Never compare yourself to him, okay?"
Even his prickly questions met gentle rebukes.
That only twisted Jun-sik's gut more.
Seo-ha was always the center of conversations here.
"Whoa! My dad says Seo-ha's heading to America?"
"Nah, I heard straight to college."
"Who's gonna help with homework in middle school? Seo-ha made it easy."
Yoo Seo-ha was always quiet.
No boasting, no favoritism.
Jun-sik learned within days that most girls in class liked him.
Nationals first place?
I'd place too if I entered.
Jun-sik needed to prove himself. He'd scoured his workbook last night for the toughest problem.
All he needed now: courage!
Seeing Seo-ha made him shrink, but he mustered it.
"You're good at math, right?"
"Huh?"
Caught off-guard, Seo-ha flinched.
"I brought a problem..."
Jun-sik fumbled open the book.
Then the kid peeking from behind bounced out gleefully.
"Wow! Big bro likes numbers too?"
Sudden curveball—Jun-sik's mind blanked. But he caught on.
"Uh... yeah. I do."
"Yay! Play with me then. Number game!"
Playing with a five-year-old? But her expectant face softened him.
Just humor her quick, then get to business. Numbers are my forte anyway.
"Sure. What're we playing?"
"Prime chain!"
Seo-eun puffed up proudly.
Even Jun-sik found her adorable.
Seo-ha's awkward expression brightened.
"Let's all play then."
Jun-sik hurriedly asked.
"W-wait. What's prime chain?"
"Saying primes in order. We did this as kids. Start from the smallest, take turns."
"Yeah! I beat Mom and Dad. Big bro and Soo-jung sis lose, and kindergarten kids won't play with me."
Unlike the parents, Seo-ha didn't throw games to his sister.
Jun-sik nodded.
"Oh! No problem then. Let's go."
The game began.
"2."
"Three!"
"5."
"7."
He thought it'd end fast. It didn't.
Numbers surpassed 100.
"101."
"One-oh-three!"
"...107."
A slight delay.
Sweat trickled down Jun-sik's back.
They blew past 200.
"227."
"Two-twenty-nine!"
Jun-sik's face lit up.
The kid slipped.
"Huh? That's not prime."
"Hehe. I win!"
Ignoring him, Seo-eun jumped up and wiggled in a goofy dance.
It oddly grated.
"It is prime. Check."
Divisibility confirmed: prime.
Jun-sik's face flushed with shame.
"L-let's go again!"
Hellish prime chain resumed from the mistake.
Jun-sik lost every round so far.
At first, mere slips. But only he kept erring.
His voice grew quieter.
He'd come to challenge Seo-ha on problems, not this.
"439."
"Four-forty-three!"
Jun-sik's turn. Mind went blank.
467? 469? 471?
Numbers spun wildly in his head.
"Four... four..."
Words stuck.
Throat clogged.
"What's wrong, big bro?"
Seo-eun eyed him puzzled.
Jun-sik's eyes reddened.
"N-nothing. I gotta go."
He snatched the workbook and bolted before drinks arrived—even before shoes fully on, fleeing outside.
"Huh? Seo-ha, what about your friend?"
Mi-young entered with cola and juice on a tray, watching his retreating figure.
"He played with Seo-eun and left."
Her daughter grinned cheekily, pleased.
"What a sweet kid."
Seo-ha and Seo-eun nodded together at Mi-young's words.
Jun-sik never spoke to Seo-ha again after that day.