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| Tsumego Pro - Basic Tesuji #10 http://www.lifein19x19.com/viewtopic.php?f=11&t=11003 |
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| Author: | Drew [ Thu Oct 30, 2014 9:58 pm ] |
| Post subject: | Tsumego Pro - Basic Tesuji #10 |
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? |
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| Author: | MagicMagor [ Thu Oct 30, 2014 11:28 pm ] |
| Post subject: | 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. |
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| Author: | Cassandra [ Fri Oct 31, 2014 12:11 am ] |
| Post subject: | Re: Tsumego Pro - Basic Tesuji #10 |
MagicMagor wrote: Just for comparison, this is what happens when white can play first: Black 3 is Self-Atari, so White 4 should capture ! |
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| Author: | Drew [ Fri Oct 31, 2014 3:04 am ] |
| Post subject: | Re: Tsumego Pro - Basic Tesuji #10 |
MagicMagor wrote: 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".I don't understand how this makes ko. What I see is 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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| Author: | EdLee [ Fri Oct 31, 2014 3:23 am ] |
| Post subject: | |
Drew wrote: I don't understand how this makes ko. Hi Drew, it's B's turn to play, so: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  ?Drew wrote: The program's stated answer is shown below as 1-3. Sorry, what you said is a bit unclear:My objection is 4 & 6. does the program show the solution only up to  ?Or does it also include and ?Drew wrote: What I see is Same question: does the program include elsewhere and killing all the group and taking the 6 stones. , 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.Drew wrote: The reader is supposed to assume that If your program includes ... removing the 6 B stones,it's showing the local result when W wins the local ko. |
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| Author: | DrStraw [ Fri Oct 31, 2014 5:09 am ] |
| Post subject: | Re: Tsumego Pro - Basic Tesuji #10 |
Cassandra wrote: MagicMagor wrote: Just for comparison, this is what happens when white can play first: Black 3 is Self-Atari, so White 4 should capture ! White should not play 4. No need to. He should ignore it. |
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| Author: | Drew [ Fri Oct 31, 2014 7:07 am ] |
| Post subject: | Re: |
EdLee wrote: Drew wrote: I don't understand how this makes ko. Hi Drew, it's B's turn to play, so: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 ?Drew wrote: The program's stated answer is shown below as 1-3. Sorry, what you said is a bit unclear:My objection is 4 & 6. does the program show the solution only up to ?Hi Ed, 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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| Author: | EdLee [ Fri Oct 31, 2014 11:16 am ] |
| Post subject: | |
Drew wrote: because I didn't consider the possibility of a ko threat Hi Drew, you're welcome.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. |
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