Guess the kosumi

White to play a kosumi.

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Is hane at the head of two stones still technically a kosumi? I’m not sure if the proximity of the black stones changes it…

Otherwise I guess maybe G7? :thinking:

None of your two suggestions is the game move.

Hint: don’t answer locally.

M7, move out and threaten to cut?


Correct !


Live from the Italian championship, commented by Tanguy Le Calvé on twitch.

Black to play a kosumi.


J11 (to defend the group K10)?

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Game: XLIII Italian Go Championship - Final - 2nd game
Commentary: Twitch: European Go Federation, XLIII Italian Championship


Davide Bernardis is young and strong (among Italian players). I met him at a tournament when he was a nice boy with long elegant fingers. He was already very strong.
He then grew up and now is a very tall young man even stronger.

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Black to play a kosumi:

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This one seems difficult




J5 maybe?

Though F17 looks nice.



I would never call F17 a kosumi.


I think that’s probably something that could do with being established.

Since otherwise it’s completely arbitrary

what one might “call” a kosumi. Just in that each person looking to post a puzzle might have different ideas about what counts.

So more generally should a kosumi be a “free-standing” kosumi, or if it’s part of another shape should it no longer count as a kosumi?

Edit: for the rules of the game I mean, to make guessing simpler, and more people can jump in easily. Outside of the game it doesn’t matter really.

“Shape” is a bit too general to completely forbid a kosumi which is part of a larger shape. For instance, a kosumitsuke is still a kosumi.
But at the very least, I would always require that the two points adjacent to both of the kosumi’s two stones should be empty.

Otherwise, it’s not a kosumi, but rather an empty triangle or a hane (or atari).

Go4Go Free_2022-11-01-12-39-39

Go4Go Free_2022-11-01-12-41-48
Not a kosumi

Go4Go Free_2022-11-01-12-40-44
Not a kosumi


To construct practical/useful puzzles, one might want to accept as an answer all of several good kosumis, not just the one that a pro ended up playing.

Which probably means AI analysis could help with puzzle construction: either to help select pro kosumi moves for which there wasn’t another reasonable kosumi option, or to actually have the AI provide the multiple move options.

I’m in favour of using human pro moves for puzzles rather than AI moves, which means I vote for using AI to eliminate puzzles for which the pro move isn’t the only good kosumi.

Or you could rewrite the text of the puzzle as: “In this situation, Black played a kosumi. The AI preferred another kosumi instead. Find both the kosumi that was played, and the kosumi recommended by the AI”

Answer: Cho Chikun (9p) vs. Takemiya Masaki (9p) | Waltheri's go pattern search

Takemiya explaining the move.

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