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| 3 L&D problems from an ancient Chinese game http://www.lifein19x19.com/viewtopic.php?f=15&t=2691 |
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| Author: | hiyayang [ Sun Dec 26, 2010 10:38 am ] |
| Post subject: | 3 L&D problems from an ancient Chinese game |
Taken from a year-old post at Tom Weiqi Forum (http://club.weiqi.tom.com/item_111_1456663_0_7.html). It was an H3 game between Zang Nianxuan (W) and Fang Zuozhou in Qing Dynasty (circa 1700 AD). Problem #1. Level: Easy (for SDKs?) Position at move 94
White to play. What's the status of the black group on the right side? Specifically, if white plays 'a', can black live? |
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| Author: | Gresil [ Sun Dec 26, 2010 11:05 am ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
A nice problem! I can't find anything. Position at move 94
Not this  —the ladder doesn't work. Position at move 94
Not this either.Position at move 94
Transposes to the ladder. Position at move 94
The same ladder again. Position at move 94
Nah. |
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| Author: | Numsgil [ Sun Dec 26, 2010 11:16 am ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
@Gresil What about aiming for a loose ladder? Position at move 94
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| Author: | Gresil [ Sun Dec 26, 2010 11:40 am ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Whoops. |
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| Author: | hiyayang [ Sun Dec 26, 2010 2:09 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Nice job, Numsgil and Gresil! Gresil was just one move away from the solution, but he saved me a lot of work posting the variations.  For beginners, here is a variation that most people first thought about and that didn't work (with a correction to one of Gresil's variations): Black fails, after white captures the black stone at S6
At this point, neither 'a' nor 'b' works for black. White can also play  at  , to the same effect. Actually, there is a bonus question derived from this:
How does white escape? Does 'a' work? |
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| Author: | hiyayang [ Sun Dec 26, 2010 2:40 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Spoiler alert: Stop here if you want to work on the first problem, as the diagram below contains the spoiler. Problem #2. Level: Medium Position at move 157
Black to play. How does the black group extending from lower-right corner to center live? Hint: Running out is not an option. |
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| Author: | Gresil [ Sun Dec 26, 2010 2:55 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
This  seems to work:Position at move 157
Without it black only gets a ko from the atari of M6: Position at move 157
But can't black live by just extending his eyespace? Does white have a more severe attack than than this  ?Position at move 157
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| Author: | hiyayang [ Mon Dec 27, 2010 6:05 am ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Hint (and @ Gresil): Note that White has a series of sente moves to threaten the black group on the right. For example,
Therefore, you have to be careful not to play moves that could get either black group killed. |
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| Author: | hiyayang [ Mon Dec 27, 2010 6:09 am ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
@Gresil:
How would black respond to ? |
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| Author: | hiyayang [ Fri Dec 31, 2010 7:43 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Solution to Problem #2: In the actual game the following moves were played, which are believed to be optimal -- Moves 158 to 167, black to live with ko
Moves 168 to 177, 9 at 1
Moves 178 to 187, 8 at 2
I will post some variations next. |
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| Author: | hiyayang [ Fri Dec 31, 2010 8:16 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Assessment of the situation: Moves 158 and 159
It has already been hinted that W 'a' is sente, forcing B 'b'. In addition, W 'c' or 'd' is sente, forcing B 'e'. OTOH, B 'c' is also sente, forcing W 'd' (and then H6 when B puts the two white stones in atari). And B has to watch out for the cut at 'f'. With these in mind, you will see that B's options to live the LR group without getting his other groups killed are really limited, hence . |
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| Author: | hiyayang [ Fri Dec 31, 2010 9:39 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Black failure #1: Trying to live without ko, B ends up getting his group killed -- Black group dies
Note: 1. B 'a' is not sente (because W 'b' is), otherwise W  would be unable to go home.2. It is important that B 'c' does not force W 'd', otherwise B could throw in at 'e' to live. Therefore, W has to be careful with , as he would get an inferior result by playing this way:White fails
Later B 'a' would enable a ko at 'b' or a throw-in at 'c' as described above. |
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| Author: | hiyayang [ Sat Jan 01, 2011 3:42 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Variation #1: So double hane to live with ko is the best result B can hope for in this situation. Now W has a choice. If W avoids the ko, B lives: White backs off; Black lives
Then B 'a' lives. But why should W be afraid of the ko fight? He has virtually nothing to lose here -- even if B won the ko fight, the W group in the LR corner is still alive: Moves 190 to 191
That is, even if W got cut at 'b' and B played the circled stone (to destroy W's eye) instead of the actual game move 'a' (to give W fewer ko threats). Then, whether B plays  or 'd',  secures the eye at 'c'.W just has to make sure he gets compensated elsewhere for the loss of the ko fight. |
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| Author: | hiyayang [ Sat Jan 01, 2011 4:12 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Black failure #2: Point wise, fighting the ko in the center is less advantageous for B than in the corner: After move 157
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| Author: | hiyayang [ Sat Jan 01, 2011 4:30 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Variation #2: In previous diagram, W has to be careful with the ko threat . For example, I don't think in the following diagram would work out for W:After move 157
The problem with this is that it allows B to cut in sente (  ). As a result, the marked white stone would have to run in gote. |
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| Author: | hiyayang [ Sat Jan 01, 2011 4:39 pm ] |
| Post subject: | Re: 3 L&D problems from an ancient Chinese game |
Spoiler Alert: The diagram below contains answers to previous problems! Problem #3. Level: Difficult The black group extending from the upper-right corner to center is surrounded. Can it live? Position at move 195, Black to play
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