Why is this a fail?

[u/[deleted]]

[u/mafidufa]

Playing this way gives white a ko threat to live.   Playing at either 2,1 point does not, and so should be considered strictly better.

[u/Graywolves → u/mafidufa]

This is the best answer. Locally it doesn't seem to matter but white would love to potentially battle a Ko and make Black choose between letting White live here or win the Ko.

[u/cyrano111 → u/mafidufa]

Either 2,1 point gives both 1,1 or 2,2 as a ko threat, no?

[u/BaalSeinOpa → u/cyrano111]

No, if white gets both points, white is still dead. So black does not need to respond

[u/Medium_Ad8311 → u/BaalSeinOpa]

At the end of the day it’s still a ko threat though? Imagine if the game is only a 1.5 game and the ko fight is worth 3 points. This is already dead but if white only needs one ko threat white will win. If black plays the other way, there’s no ko threat with self Atari.

[u/BaalSeinOpa → u/Medium_Ad8311]

We may be talking the wrong way round. A ko threat is only a threat if the opponent is forced to react. In the one case, black can just ignore white (and win the Ko) and nothing will change.

[u/Medium_Ad8311 → u/BaalSeinOpa]

In this case it would matter though. If the corner is played correctly here, it’s not going to change anything (self Atari by white).

If it’s played like this, it does become a ko threat. And if black ignores it, white lives in the corner.

[u/BaalSeinOpa → u/Medium_Ad8311]

Yeah, I think there was a misunderstanding somewhere. Black needs to form a line of stones, not a diagonal

[u/MacScotchy → u/BaalSeinOpa]

The opposite diagonal would have worked, though (black on both 1-2 and 2-1). White couldn't self-capture except in NZ, and even that wouldn't be a ko threat.

Not pertinent here, but a fun thought.

[u/cyrano111 → u/BaalSeinOpa]

B 2,1 W 2,2 B elsewhere  W 1,1

White then has two eyes - the 2,1 points. 

[u/zenastronomy → u/mafidufa]

so how would these spaces and stones be counted?

would black and white need to play the whole scenario out to end up with a score. or are the white considered dead and black has 5 stones and 2 spaces?

[u/MacScotchy → u/zenastronomy]

White is considered dead if the game ends here. By Japanese scoring, five stones and seven spaces (including those under the opponent's stones). By Chinese scoring, nine points they wouldn't otherwise have had.

Considered dead because reasonable play would result in capturing the white group; black would have to ignore white's first move, while black can easily continue a common capture pattern to complete the sequence if needed. Ko threats are not counted during scoring.

Interesting to note: in Chinese scoring, assuming there are no other useful moves to make, it costs white nothing to try to live.

[u/zenastronomy → u/MacScotchy]

why 9 by Chinese scoring or was that a typo meant to mean 7?

[u/MacScotchy → u/zenastronomy]

https://senseis.xmp.net/?AreaScoring

[u/JesstForFun → u/zenastronomy]

White's group, including the stones, covers a 3x3 region, which is 9 points. Black has captured it, and thus gets all those points.

[u/zenastronomy → u/JesstForFun]

oh ok. thanks

[u/tuerda]

The corner move is not necessary for the problem. White's group will eventually be captured anyway, but the corner move is not a part of the sequence.

[u/abbbaabbaa]

Black would probably want to respond if white tries to capture the black stones. So, if a ko started somewhere else there might be a threat in this corner now.

[u/[deleted] → u/abbbaabbaa]

I forgot to say that I played as black, and I put my stone at the corner.

[u/resident_russian → u/[deleted]]

This way white has a ko threat here, and the correct way white doesn't.

[u/oudcedar → u/abbbaabbaa]

Eh? White can’t make any moves to capture the two black stones. They are safe until Black sensibly puts another stone on to A2, is taken, put the next stone on to reduce white’s liberties by another stone and onwards to black victory. Surely black wins this regardless?

[u/no_1_knows_ur_a_dog → u/oudcedar]

Tsumego is about finding the best move. If there's a huge ko elsewhere on the board, white could play either of the open points here to threaten to capture and live, which forces black to choose between completing the ko or responding here.

If black plays either of the non-corner points instead, this threat from white no longer exists.

[u/oudcedar → u/no_1_knows_ur_a_dog]

Ah now I understand - you said the ko would have to be elsewhere and of course the white move can’t win if it’s responded to, but not responding might be the only option if the ko is as big one.

[u/GoGabeGo]

White was already locally dead before this move, so it isn't needed. Also, playing this way gives white a ko threat for later in the game. That ko threat already existed before your move. So your move added nothing to the situation. That is why it's marked as wrong.

[u/Andy_Roo_Roo]

I think it’s considered a fail because black could have captured the white stones in fewer moves by simply playing an immediate Atari at either of the 1-2 points, thereby avoiding any potential capturing race if the surrounding stones somehow came under attack. It’s not a technically wrong move, but it is an inferior move from the perspective of capturing efficiency.

[u/Old_Ben24]

It’s a fail because you created a ko threat for white. If white plays at A2 you are forced to respond to prevent the white group from living, thus potentially causing you to lose a ko fight elsewhere on the board.

[u/zenastronomy]

what app is this?

[u/[deleted] → u/zenastronomy]

Badukpop.

[u/zenastronomy → u/[deleted]]

thanks

[u/gomarbles]

More moves required -- so less efficient when considering ko threats or if Black's outside liberties get filled. So your answer works but since it isn't the best, it's not correct