When i was doing some Tsumego on OGS i stumbled across the following problem: https://online-go.com/puzzle/15017

There are a few variations to this and in the one, where white connects at R17, black T17 and then white S19 the solution states, that black can live with either A, B or C...

Click Here To Show Diagram Code

[go]$$
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . 2 . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O 1 |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . . . . . O X . c . |
$$ | . . . . . . . . . . . . . . O X . b . |
$$ | . . . . . . . . . . . . . . O X X X a |
$$ | . . . . . . . . . . . . . . O O O O . |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

...but i can not really find a way for black to live with any of those options.


A: After , hits the vital point:

Click Here To Show Diagram Code

[go]$$
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . . . . . O X . . . |
$$ | . . . . . . . . . . . . . . O X . 2 . |
$$ | . . . . . . . . . . . . . . O X X X 1 |
$$ | . . . . . . . . . . . . . . O O O O . |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

B: After white answers with and again i can't find out how black is supposed to live here:

Click Here To Show Diagram Code

[go]$$
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . . . . . O X 2 a b |
$$ | . . . . . . . . . . . . . . O X . 1 . |
$$ | . . . . . . . . . . . . . . O X X X c |
$$ | . . . . . . . . . . . . . . O O O O . |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

Neither A, nor B serve the task and because white has an Atari at A, things like C into B also don't quite work out, as it seems.


C: Similar to B. After white plays the vital point black seems to be shut down:

Click Here To Show Diagram Code

[go]$$
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X c |
$$ | . . . . . . . . . . . . . . O X . 1 . |
$$ | . . . . . . . . . . . . . . O X 2 a b |
$$ | . . . . . . . . . . . . . . O X X X . |
$$ | . . . . . . . . . . . . . . O O O O . |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

If black answers at A, white will play Hane into C, after black blocks and if black B, white C does the job immediately. If black plays see i would think that white B kills the black group.




Most of the problems of this collection are well above my current skill, so i wouldn't be surprised if i overlooked some obvious things, but i would be very interested to know what those things are

How do you get to that position? I looked at the puzzle and the correct answer never gets to the position you show.

I agree, the puzzle looks flawed to me. I haven't used the OGS problem interface much: there isn't a way to browse the variations, other than resetting the puzzle over and over again and trying different responses?

Click Here To Show Diagram Code

[go]$$
$$ ------------+
$$ . . . . O . |
$$ O . O O X X |
$$ . O . O O X |
$$ . . O O X O |
$$ . . O X X a |
$$ . O X . 3 . |
$$ . O X b 2 . |
$$ . O X X X 1 |
$$ . O O O O . |
$$ . . , . O . |
$$ . . . . . . |
$$ . . . . . . |[/go]

After B3, it played white 'a' which looks like a mistake. I can't see a way to live after white 'b' instead.

Click Here To Show Diagram Code

[go]$$
$$ ------------+
$$ . . . . . . |
$$ O . 4 O 3 5 |
$$ . 2 1 B O . |
$$ . . O O X O |
$$ . . O X X . |
$$ . O X . . . |
$$ . O X . . . |
$$ . O X X X . |
$$ . O O O O . |
$$ . . , . O . |
$$ . . . . . . |
$$ . . . . . . |[/go]

at

Oops, what I said below is completely wrong.

Click Here To Show Diagram Code

[go]$$ Black lives in seki
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X 5 |
$$ | . . . . . . . . . . . . . . O X . 1 . |
$$ | . . . . . . . . . . . . . . O X 2 4 6 |
$$ | . . . . . . . . . . . . . . O X X X 3 |
$$ | . . . . . . . . . . . . . . O O O O . |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

Click Here To Show Diagram Code

[go]$$ Really ???
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X . |
$$ | . . . . . . . . . . . . . . . O X X X |
$$ | . . . . . . . . . . . . . . O X . X . |
$$ | . . . . . . . . . . . . . . O X O O O |
$$ | . . . . . . . . . . . . . . O X X X X |
$$ | . . . . . . . . . . . . . . O O O O 8 |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]

_________________
The really most difficult Go problem ever: https://igohatsuyoron120.de/index.htm
Igo Hatsuyōron #120 (really solved by KataGo)

@yoyoma & xela

You just have to play T18 over and over again. Sometimes white will hane at T12, sometimes connect T17 and then sometimes play R17, which will lead to this position. Unfortunately i could not find a way to look at or download the sgf tree.
After i had played around with the puzzle for a good while i reset it, to play from the start und white kept playing the hane.. for a second there i thought i was hallucinating over a variation that was not in the original problem for the previous 30min or so (OGS seems to add replies you play after a finished position to the problem tree, as i noticed before).



@jlt

As Cassandra pointed out the Seki does not really work, because of the cutting point in blacks position. I tried a similar result after black replies at C, but i never worked, because of whites atari at A:

Click Here To Show Diagram Code

[go]$$
$$ +---------------------------------------+
$$ | . . . . . . . . . . . . . . . . . O . |
$$ | . . . . . . . . . . . . . O . O O X X |
$$ | . . . . . . . . . . . . . . O . O O X |
$$ | . . . , . . . . . , . . . . . O O X O |
$$ | . . . . . . . . . . . . . . . O X X . |
$$ | . . . . . . . . . . . . . . O X . 1 5 |
$$ | . . . . . . . . . . . . . . O X 2 4 6 |
$$ | . . . . . . . . . . . . . . O X X X 3 |
$$ | . . . . . . . . . . . . . . O O O O a |
$$ | . . . , . . . . . , . . . . . , . O . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]

Oops...

Could this be an unfinished problem? I played with it a bit and many branches, even promising ones just say "incorrect" without explanations, once I even had an "incorrect" message in a position that was already alive.

Depending on the problem setter, this IS possible. For example, if the problem is "black move and live" there might be several possibilities that left black alive. But living in seki might be marked wrong if it was possible to live with points or live in gote marked wrong if it was possible to live in sente, etc.

bad problem - just move on

_________________
be immersed

Probably the author saw the "seki" and didn't bother double checking his solution further. I will admit my first instinct on seeing the position was "no, he's mistaken, this must be alive", but no, it isn't.



Or even simply sacrificing some stones to live while you don't have to (a particularly amusing situation is when due to a sacrifice the seki variation is worth more points than the "alive with points" variation).

(Also I personally think that in situation which you have the choice between making a ko or a seki you haven't solved the problem unless you've seen both variations).

None of these seems too relevant given the problems to make any life here.