I was solving some problems from the Graded Go Problems for Beginners Vol. II, and I am a bit confused about one of the given answers to a problem (54). Given the diagram below, the instructions are to find how Black should play in response to White 1. The most obvious choices seem to be Black at A, B, or C. After some consideration, I thought that A seemed to be the best answer. After all, this seems to give Black some more influence on the outside, while providing a solid connection of four stones.
However, the given answer is Black to play at B. After being somewhat surprised at the answer, I played out what seemed to be the most likely sequence to follow (see diagram below) and I don’t understand the advantage that this gives black, especially after White plays the cut at 4, and then escapes with 6. I guess that Black could then cut at A, followed by White playing the atari at B, but I still don’t see how this is the best sequence for Black.
Also, if black decides to respond to White 1 in the above diagram by setting up a bamboo joint at C, he can then keep his two pairs of black stones connected no matter what White plays next. So, in conclusion, both Black plays at A and C in the above diagram seem to be better choices than the given answer of B.
The correct answer (B, first diagram) in the back of the book merely states that this move is a basic joseki. The given incorrect answer (Black to play at A in the first diagram) states that White then moves into the corner at B, and that White suffers a big loss, but it seems to me like this gives Black some outside influence in compensation, without having his stones cut. Could someone please explain this? Thanks!
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 12:27 am
by Go_Japan
I could be wrong, but I think the best response to White 4 is to play Black at 6. If white escapes the atari, extend along the bottom. White cannot easily kill the 3 black stones.
White cannot play the cut. Black can play as below because white can only protect against one of a and b (I think the cut directly probably works too, but more complicated).
The 3-3 point at 1 is so incredibly important, not just in terms of points, but also for group stability. Compare the two corners below and see if you feel the MASSIVE difference in terms of corner points and group strength (though here black has the 4-10 points, so the black group is not that much weaker).
The lower left is the joseki, the upper right is the bad shape (http://senseis.xmp.net/?EmptyTriangle) block. Note in both cases it's white to move next, so there's no difference due to an extra move.
Also, note that the lower left is better in terms of "influence" as well - the top right group is actually WEAKER due to bad shape in comparison.
) ( ;W[er] ;B[fr] ;W[cr] ;B[br] ;W[bs] ;B[ar] ;W[bo] ;B[ap] ;W[fs] ;B[gr] ;W[dq] ;B[ds]C[*** Eye vs no eye. Black wins.] )
) ( ;W[bo]C[*** Does not work.] ;B[cm] ;W[bm] ;B[cl] ( ;W[bl] ;B[ao] ;W[bn] ;B[ck]C[*** Both Black and White have only four dame.] ( ;W[eq]C[*** The best White can do.] ;B[dr]C[*** Black secures the corner and the White stone on the left die a dog's death. Now you can see the value of the descent before playing atari on the cutting stone.] ) ( ;W[dq] ;B[cr] )
) ( ;W[an] ;B[fp] ;W[eq] ;B[fq] ;W[dr] ;B[ap] ;W[ao] ;B[fr] ;W[br] ;B[bl] ;W[bq] ;B[al] ;W[aq] ;B[am] ;W[cq] ;B[bn]C[*** Very bad for White. White has small life in the corner. See continuation after pass.] ;W[tt] ;B[cs] ;W[ds] ;B[bs] ;W[as] ;B[ar] ;W[cr]C[White can also pass and save this for later.] )
)
)
Edit: Added a couple of variations.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 1:12 am
by illluck
There are more difficult lines of resistance by white (e.g. an empty triangle to remove a liberty rather than connect - though here black's stone on the left side probably removes the danger), but overall the idea is that the cut does not work (though I'm not confident I'll play it correctly :p).
Posted: Tue Feb 07, 2012 1:46 am
by EdLee
txcpa,
See Bill's variations.
txcpa wrote:...seems to give Black some more influence
At these levels (up to around maybe 1d), whenever you see or hear yourself say the word "influence," mentally replace it with "magic" (or "gobbledigook" if you like) -- and there is almost zero loss of information.
Your first feeling of (a) should be suspect to you right away because it makes an empty triangle (not a good shape in this case):
Each of extend (in reply to hane), extend, and block is a basic shape; and together - is a basic sequence (thus "basic joseki" in the book). There are literally millions of these.
What if W omits ? B could make a very powerful shape:
(That's why extend and B's tiger's mouth share a very big local vital point.)
You asked a very good question. Keep playing and studying. Enjoy.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 5:38 am
by blade90
If you are a beginner then what you must really know is: Black 'a' prevents white to dive into your corner, why is that important? There are 2 reasons: 1. Black secures most of the corner by playing a 2. If black closes the corner then white does not have a base yet + he still has a cutting point, in other words white is not alive and will come under attack.
The most important is 2. of course. If white follows the joseki he will not push and cut but make a hanging connection to protect the cutting point - this also creates a small base, and white the one point jump (this is shown in illluck's 2nd dia.). Note that white can still be attacked later, this group is pincered and even if it lives it is not worth much.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 6:02 am
by tj86430
blade90 wrote:If you are a beginner then what you must really know is: Black 'a' prevents white to dive into your corner, why is that important? There are 2 reasons: 1. Black secures most of the corner by playing a 2. If black closes the corner then white does not have a base yet + he still has a cutting point, in other words white is not alive and will come under attack.
You mean 'b' in the original diagram, not 'a', right?
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 6:54 am
by Go_Japan
illluck wrote:White cannot play the cut. Black can play as below because white can only protect against one of a and b (I think the cut directly probably works too, but more complicated).
Thanks for this play B at 7. I learned something today.
As others have said, blocking in the corner is the key point to make eyes and territory for yourself, and deny the same to white. It is good that you considered black's weakness of white pushing through and cutting, and even better that you also saw white had a weakness (the cut at a in txpca's 2nd diagram. These weaknesses sort of cancel out and mean that black can handle the fight if white does cut. In white already had a stone which defended his cut, then blocking the corner would be much more dangerous as white's push and cut becomes much more powerful as he is not held back by his own weakness. This is a really common idea in Go.
Another general principle I would learn from this position is as follows. You should want to block the corner at b as, if it works, it gets you the most. But then you worry about white's cut. If you can read that white's cut results in your instant death the change your plan. But if you are not sure, play the possibly greedy move. It is better to ask for too much, and then learn why it is wrong, than to always play timidly.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 8:38 am
by Bill Spight
Aside on the equivalence at the kyu level of influence and magic, or gobbledygook:
There are those of us who, even as beginners, wanted to be magicians. It is never too early to become a sorcerer's apprentice. Sure, disasters happen, but they happen, anyway. Better to get your feet wet than to say you cannot swim.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 9:42 am
by txcpa
Great responses, everyone! I appreciate the analysis. I was wondering if bad shape might have been part of the problem, but I don't quite yet know enough to be able to clearly discern the differences between some shape concepts such as thickness vs. heaviness. I've read Volumes I-III in the Learn to Play Go series (and most of Volume IV), and most of Opening Theory Made Easy, so I'm familiar with such concepts (including the empty triangle), but I am not yet at the point of truly understanding why something is bad shape or good shape, but I guess that such intuition just comes with more experience. I'm continually amazed at the complexity of this game, and am very much enjoying my study of it.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 9:44 am
by Bill Spight
illluck wrote:There are more difficult lines of resistance by white (e.g. an empty triangle to remove a liberty rather than connect - though here black's stone on the left side probably removes the danger), but overall the idea is that the cut does not work (though I'm not confident I'll play it correctly :p).
I added a couple of variations for that play.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 9:57 am
by Bill Spight
txcpa wrote:Great responses, everyone! I appreciate the analysis. I was wondering if bad shape might have been part of the problem, but I don't quite yet know enough to be able to clearly discern the differences between some shape concepts such as thickness vs. heaviness.
If you can fairly reliably distinguish thick from heavy and thin from light, you are strong for an amateur.
I've read Volumes I-III in the Learn to Play Go series (and most of Volume IV), and most of Opening Theory Made Easy, so I'm familiar with such concepts (including the empty triangle), but I am not yet at the point of truly understanding why something is bad shape or good shape, but I guess that such intuition just comes with more experience. I'm continually amazed at the complexity of this game, and am very much enjoying my study of it.
Shape is essentially about making your stones work together efficiently in a local region. Sometimes amateurs will say, oh, this is a good shape, with no consideration of the context. A shape that may be good to counter an opponent's threat may be inefficient if the opponent has no such threat.
Re: Confused about an opening sequence
Posted: Tue Feb 07, 2012 10:12 am
by blade90
tj86430 wrote:You mean 'b' in the original diagram, not 'a', right?
(a) should be suspect to you right away because it makes an empty triangle
extend (in reply to 
hane), 
extend, and 
block is a basic shape;