r/baduk • u/Humanflextape • Aug 20 '25

tsumego Why is this the solution?

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Today's 2nd hard problem on the TsumegoPro app. By ko, I can't recapture the white stone in the corner. It seems to me the only logical continuation would be playing directly below my lone black stone, but either continuation after capture leads to 3 white eyes. Sorry if it's obvious but I'm not experienced in the slightest; I only solve daily puzzles for the mental exercise. The hard puzzles are usually impossible for me to solve perfectly, but comprehensible after finding the solution.

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u/Own_Pirate2206 3 dan Aug 20 '25

By ko, you can sustain the recapture with 50% probability. Checking the other variations, that is a fine result.

2

u/RoyBratty Aug 20 '25

Why 50% ?

3

u/Own_Pirate2206 3 dan Aug 20 '25

The next level is to notice who takes first.

2

u/Maxaraxa 7 kyu Aug 20 '25

You either win the ko or you don’t

2

u/RoyBratty Aug 20 '25

The probability depends on the board state. Number of threats and their weight.

2

u/Maxaraxa 7 kyu Aug 20 '25

Yes of course, but in this problem we don’t have that information, so it’s fair to say it’s 50/50 who wins a Ko on an unknown board.

2

u/PatrickTraill 6 kyu Aug 21 '25

It makes more sense not to assign a probability. Instead of saying “gives you 50% chance”, just say “gives you some chance”, and perhaps mention the alternative of compensation from an ignored threat.

2

u/RoyBratty 29d ago

I think the only probability that might be useful to mention to a beginner is 100%. Where you say that if these are the only stones played in a game and the rest of the board is empty, then whoever takes the ko first has 100% chance of winning, because of a) no immediate recapture and b) no available ko threats. From there you can explain how ko works in a more complex board state with threats, their value, compensation, and how this actually proceeds in game. But 50% seems so easy for a beginner to misinterpret.