I'm confused by this problem because I don't see any "win" for black. The program's stated answer is shown below as 1-3.
My objection is 4 & 6.
Is the problem in error? Or am I missing something terribly obvious?
Tsumego Pro - Basic Tesuji #10
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MagicMagor
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Re: Tsumego Pro - Basic Tesuji #10
Yes you are missing 
After
the situation turns into a Ko. Living without Ko is usually better than Ko, but Ko is better than plain dying. So the answer is "Black can make Ko with 1 and 3".
Just for comparison, this is what happens when white can play first:
Now black can't connect because it is self-atari, so black is outright dead.
After
the situation turns into a Ko. Living without Ko is usually better than Ko, but Ko is better than plain dying. So the answer is "Black can make Ko with 1 and 3".Just for comparison, this is what happens when white can play first:
Now black can't connect because it is self-atari, so black is outright dead.
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Cassandra
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Re: Tsumego Pro - Basic Tesuji #10
Black 3 is Self-Atari, so White 4 should capture !MagicMagor wrote: Just for comparison, this is what happens when white can play first:
The really most difficult Go problem ever: https://igohatsuyoron120.de/index.htm
Igo Hatsuyōron #120 (really solved by KataGo)
Igo Hatsuyōron #120 (really solved by KataGo)
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Drew
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Re: Tsumego Pro - Basic Tesuji #10
I don't understand how this makes ko. What I see isMagicMagor wrote:Yes you are missing
After
elsewhere and 
killing all the group and taking the 6 stones. The reader is supposed to assume that is a sufficiently large ko threat played elsewhere on the board to make playing at the key point a bad decision? Couldn't you use that logic to solve every tsumego?!? 
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EdLee
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Hi Drew, it's B's turn to play, so:Drew wrote:I don't understand how this makes ko.
Where can B play locally, and what are the different results, locally ?
Can you see, and do you agree, that if B does not play at the solution (x),
but anywhere else, then W can kill at least
?
Sorry, what you said is a bit unclear:Drew wrote:The program's stated answer is shown below as 1-3.
My objection is 4 & 6.
does the program show the solution only up to
?Or does it also include
and ?Same question: does the program includeDrew wrote:What I see is
, removing the 6 B stones, or is that your continuation ?After
hane, starts the ko.Suppose
is a ko threat elsewhere, and W replies with (also elsewhere).Then B can re-take the local ko with
, which gains an important liberty for B --now the big B group momentarily has 2 liberties: This means that if -- an important if --
B has the chance to play at (a) while the 6 B stones are not in atari,
then B kills W here, and B lives.
Which is better than simply dead for B.
This is why the solution
is a ko.If your program includesDrew wrote:The reader is supposed to assume that
removing the 6 B stones,it's showing the local result when W wins the local ko.
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DrStraw
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Re: Tsumego Pro - Basic Tesuji #10
White should not play 4. No need to. He should ignore it.Cassandra wrote:Black 3 is Self-Atari, so White 4 should capture !MagicMagor wrote: Just for comparison, this is what happens when white can play first:
Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).
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Drew
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Re:
Hi Ed,EdLee wrote:Hi Drew, it's B's turn to play, so:Drew wrote:I don't understand how this makes ko.
Where can B play locally, and what are the different results, locally ?
Can you see, and do you agree, that if B does not play at the solution (x),
but anywhere else, then W can kill at leastSorry, what you said is a bit unclear:Drew wrote:The program's stated answer is shown below as 1-3.
My objection is 4 & 6.
does the program show the solution only up to
It stops at
and marks itself solved. I meant that was played elsewhere because I didn't see how it could possibly stave of locally, which is because I didn't consider the possibility of a ko threat outside the scope of the problem.I can understand how the ko is possible now, thank you. Just too inexperienced with tsumego to understand what they were after.
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EdLee
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Hi Drew, you're welcome.Drew wrote:because I didn't consider the possibility of a ko threat
Yes, these are standard conventions: when a tsumego shows you only the local situation:
- if a ko develops, you have to look at all the local threats (if any), and we don't know about the global threats, because they depend on the rest of the board.
- usually you can assume all global ladders (not shown) are good for B, unless explicitly specified otherwise.