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3move tsumego rule http://lifein19x19.com/viewtopic.php?f=15&t=16066 
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Author:  mitsun [ Thu Sep 13, 2018 5:14 pm ] 
Post subject:  Re: 3move tsumego rule 
Here is another problem, nicely solvable by this method. Both marked W moves seem to make two eyes immediately .... How can B play to make this not true? 
Author:  Bill Spight [ Thu Sep 13, 2018 5:37 pm ] 
Post subject:  Re: 3move tsumego rule 
Hidden out of courtesy. 
Author:  Kirby [ Thu Sep 13, 2018 10:42 pm ] 
Post subject:  Re: 3move tsumego rule 
@dfan: Thanks for explaining to me. It's easier to understand now, even at 2 in the morning :p @Bill: In your last diagram, how did you select as 'A' and not the other (lowercase 'a')? Or does selection of 'A' not matter much? By capital 'A', I'm referring to the original rule. 
Author:  Bill Spight [ Thu Sep 13, 2018 11:00 pm ] 
Post subject:  Re: 3move tsumego rule 
Kirby wrote: @Bill: In your last diagram, how did you select as 'A' and not the other (lowercase 'a')? Or does selection of 'A' not matter much? By capital 'A', I'm referring to the original rule. Well, you want to select a White move such that Black has two necessary moves to kill. I picked the one I did because it formed a one space eye. As it turned out, that fit the bill. 
Author:  Knotwilg [ Fri Sep 14, 2018 1:03 am ] 
Post subject:  Re: 3move tsumego rule 
Author:  Javaness2 [ Fri Sep 14, 2018 1:34 am ] 
Post subject:  Re: 3move tsumego rule 
John Fairbairn wrote: I do look forward to discussion of this excellent post. Matthew Macfadyen (exEuropean Champion) used to mention this principle a lot and he used it in his seminars (?around 1975~1980). As I recall, he said he got it from someone else, and some others claimed to know about it, but I never understood why it was not more widely known. My brain baulks at thing like that, so I've never tried to use it  frankly, didn't even understand it. Maybe others had the same disinclination. Or perhaps people then were not doing tsumego much. That may sound farfetched but the only collection available was the small Maeda series. I think Matthew referred to it as a 2move rule but I can't remember his exact wording. Is this the idea that the first step to solving the problem of how to kill is working out how to live? 
Author:  Tryss [ Fri Sep 14, 2018 3:09 am ] 
Post subject:  Re: 3move tsumego rule 
Knotwilg wrote: 
Author:  Kirby [ Fri Sep 14, 2018 4:18 am ] 
Post subject:  Re: 3move tsumego rule 
Knotwilg wrote: Neat. I can see these specific examples working. I'm trying to convince that this always works for different selections of 'A'  or the boundaries of when it works. I'm a little tired to think accurately now, though. 
Author:  zermelo [ Fri Sep 14, 2018 4:43 am ] 
Post subject:  Re: 3move tsumego rule 
Quote: @zermelo: One thing that interests me a lot is how other people think. Would you be willing to explain how you came up with this insight? It may be a rediscovery but it's still a discovery! And also, your view of it as a 3move principle rather than the 2move principle I first heard makes it easier for me to comprehend. I cannot really remember that well. I imagine I was looking at some difficult problem and thinking "playing at A does not work for black, but then if white gets A, black cannot kill even getting more than 1 move in a row ... no, wait a minute...". Also, thanks for nice words, John, Bill, Knotwilg. I'm sure many have come up with this, and probably many have used it without formulating it as a 'rule'. And Bill answered the technical comments and explained when the rule works already so well that I have nothing to add to that. As said, this definitely works only for some problems, and even they could of course be solved just by going through variations sequentially. Myself, I find it really comforting with some difficult problems to at least decisively limit the starting moves to e.g. three moves, and so I really like this approach when it works. As opposed to not finding a solution and thinking that now I need to again go through all the possible starting moves and variations and see where I made a mistake. So different methods could suit different personalities or psychologies too. 
Author:  zermelo [ Fri Sep 14, 2018 4:50 am ] 
Post subject:  Re: 3move tsumego rule 
Author:  Bill Spight [ Fri Sep 14, 2018 6:14 am ] 
Post subject:  Re: 3move tsumego rule 
Author:  Bill Spight [ Fri Sep 14, 2018 7:22 am ] 
Post subject:  Re: 3move tsumego rule 
Kirby wrote: I'm trying to convince that this always works for different selections of 'A'  or the boundaries of when it works. By the logic of the rule, the necessity of B and C to achieve the goal, given A, is equivalent to the assumption that the goal is achievable. The derivation of A as a possible first play depends upon the observation that if the first play is none of A, B, or C, then the defender can play at A and make miai of B and C. A has to be a good play. In this position looks like a vital point, threatening to make 3 one point eyes (marked). Then and suffice to kill. But are they necessary? No, they are not. This and also kill. If at 6, at 5 We have seen this position before. White is dead. But it looks like is necessary, as it occurs in all variations. Besides, after , a White play at 2 would make 2 one point eyes. Now the fact that is necessary after suggests that it is a good first move. The relation to the All Moves As First heuristic is no accident. Edit: Now, to see that only is necessary after in all the variations took either logic, which I did not use, or going through a number of variations. As knotwilg points out, proving necessity may entail just as much search and effort as simply proceeding directly to reading. However, if you can see or show necessity without reading, you may be able to save time and effort. 
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