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| Counting question http://www.lifein19x19.com/viewtopic.php?f=11&t=14021 |
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| Author: | Baywa [ Wed Feb 22, 2017 7:53 am ] |
| Post subject: | Counting question |
Hi! This is a very, very simple counting question. But bear with me - I'm just a beginner. The question is: "What is the value of playing at B1". I get 3+4 = 7 points. The "book" says 8 (no explanation). What did I miss? Thanks in advance! |
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| Author: | Schachus [ Wed Feb 22, 2017 7:57 am ] |
| Post subject: | Re: Counting question |
If black gets it, white a3 is not going to be a point, he will have to connect there later. That is the point you forgot to count. Edit: actually, in this case, I think the move is even bigger, beacause after white b1, a later play at d1 is sente for white, so we cannot count the exchange black d1 white c1 as sente for black. Edit2, ah I see, you also didnt count in the fact, that after black gets b1, he will later have to take the white stone out. So I now count 9 points, your 7 +1 the one above, plus 2 more for white d1 in sente -1 for that. It seems it's not that simple;) |
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| Author: | Baywa [ Wed Feb 22, 2017 8:09 am ] |
| Post subject: | Re: Counting question |
Wow, that was fast! > If black gets it, white a3 is not going to be a point, > he will have to connect there later. That is the point > you forgot to count. I was thinking about that. But if black plays at B1 first he can't play A1 because of the white stone at C2. He would first have to capture that stone, reducing his territory by 1. Only then white would have to defend at A3. So the count wouldn't change. Did I get that right? |
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| Author: | Schachus [ Wed Feb 22, 2017 8:13 am ] |
| Post subject: | Re: Counting question |
Baywa wrote: Wow, that was fast! > If black gets it, white a3 is not going to be a point, > he will have to connect there later. That is the point > you forgot to count. I was thinking about that. But if black plays at B1 first he can't play A1 because of the white stone at C2. He would first have to capture that stone, reducing his territory by 1. Only then white would have to defend at A3. So the count wouldn't change. Did I get that right? Yes that seems right(what I only noticed by edit 2). I at the moment do not count the move to be 8 points(but rather 9), so maybe if 8 is right, someone should explain it to the both of us:) |
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| Author: | Uberdude [ Wed Feb 22, 2017 8:34 am ] |
| Post subject: | Re: Counting question |
If black plays first, we will eventually end up with: If white, then: Note that when counting a gote move like this you give each player their expected sente follow-ups, so white could get 1 for 2 above, and then later black 4 for 5 (there's actually a tiny chance that white could play at 4 but that's gote, whereas black's 4 is sente to capture 1 stone and more in ko so it should be his sente move later in the game). So now you can count the difference between these 2 positions. The way I would actually do this in my head is (knowing those terminal positions) look what intersections become points for black if he gets it (triangles) and what become points for white (squares). Remember captured stones count for 2 so there's a difference of 9 here. |
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| Author: | Baywa [ Wed Feb 22, 2017 9:18 am ] |
| Post subject: | Re: Counting question |
Thanks a lot for that detailed response, Uberdude! My counting based on the exchange Wb1 (captures), Bd1, Wc1. Bd1 doesn't seem to be worth much but if W ignores, then Bc1 and W has to connect at b2, loosing one point. But it all depends on what other endgame moves there are, doesn't it? BTW: This problem is from the online course on 321go.org, Chapter 5.7.2. |
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| Author: | Bill Spight [ Wed Feb 22, 2017 10:12 am ] |
| Post subject: | Re: Counting question |
I prepared an SGF file, but Uberdude beat me to it.  Just a couple of small points. After   and  are later protective plays. x is a dame.Local result for Black: +5 After   is later sente. Black normally replies with  Later,  is sente.Local result for Black: -4 Swing = 9 Initial local value for Black: 0.5 Each gote play gains 4.5. If Black is komaster she can play . The result is the same as the main line.If White is komaster  -  is very bad for Black.
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