While trying to solve a problem, the following diagram arised (black to move):
Which is a better move for Black - A or B, and why?
(This kind of difference can be found in many other situations.)
Re: which is a better move in this position?
Posted: Fri Dec 14, 2012 6:34 am
by p2501
Just looking at it I'd say B is the only move.
edit: Forgot to tell why:
A) Gives white to much forcing moves. Don't like the shape.
B) More liberties. Puts severe pressure on the bottom left stones. Reserving which side to atari from seems good.
Re: which is a better move in this position?
Posted: Fri Dec 14, 2012 6:36 am
by Alguien
My reasoning:
- the bottom b group has 3 libs.
- the one next to it has also 3 libs.
- whoever starts removing libs wins, if he can keep removing them.
- can I pull off putting a stone on the point under B, to remove a lib from W?
- I read it as a yes:
- option 1: w ataris my stone, I extend to 'B', he extends to not die, I capture bottom.
- option 2: w extends bottom, I play 'A' and capture w on a net (or he tries to escape net and I kill the now three stone bottom group).
(paint your problem as a usual (go) diagram and I'll paint my moves on it, if you want)
[edit: ok, ok ,I'll paint it:]
$$B
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . 4 . . . . . |
$$ | . . . . . . . . . . . . 3 O X X X X . |
$$ | . . . . . . . . . . . 2 X O X O O O . |
$$ | . . . . . . . . . . . 1 O X O O . O . |
$$ | . . . . . . . . . . . 5 O X X . O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------
[go]$$Bc If White resists, he just gets a weak group. B is save.
$$ . . . . . . . . . . . . . . |
$$ . . . . , . . . . . , . . . |
$$ . . . . X . . . . . . . . . |
$$ . . . . . . . . . . . B . . |
$$ . . . . . . . . . . . . . . |
$$ . . . . . . . . a . . . . . |
$$ . . . . . . . . Q X X X X . |
$$ . . . . , . X X Q X O O O . |
$$ . . . . . . . @ X O O . O . |
$$ . . . . . . b @ X X . O . . |
$$ . . . . . . . . . . . . . . |
$$ ----------------------------[/go]
White has two groups of cutting stones. Looks to me like move B makes miai out of a and b, and one of the groups is going to die.
Move A drives the triangle group over your own cutting stone, and forces its capture, but Black gets guaranteed influence. If playing B and capturing the low group is unsatisfying, then okay, play A. But that's basically 5th line territory that you're giving up. Not seeing the rest of the board, I think it's clearly better to fight to kill one of the two white groups.
Re: which is a better move in this position?
Posted: Fri Dec 14, 2012 9:29 am
by topazg
$$Bc White is forced to capture. Very good shape for Black, too.
$$ . . . . . . . . . . . . . . |
$$ . . . . , . . . . . , . . . |
$$ . . . . X . . . . . . . . . |
$$ . . . . . . . . . . . X . . |
$$ . . . . . . . . . . . . . . |
$$ . . . . . . . . 3 . . . . . |
$$ . . . . . . . . O X X X X . |
$$ . . . . , . 1 X O X O O O . |
$$ . . . . . . . O X O O . O . |
$$ . . . . . . . O X X 2 O . . |
$$ . . . . . . . . . . . . . . |
$$ ----------------------------
[go]$$Bc White is forced to capture. Very good shape for Black, too.
$$ . . . . . . . . . . . . . . |
$$ . . . . , . . . . . , . . . |
$$ . . . . X . . . . . . . . . |
$$ . . . . . . . . . . . X . . |
$$ . . . . . . . . . . . . . . |
$$ . . . . . . . . 3 . . . . . |
$$ . . . . . . . . O X X X X . |
$$ . . . . , . 1 X O X O O O . |
$$ . . . . . . . O X O O . O . |
$$ . . . . . . . O X X 2 O . . |
$$ . . . . . . . . . . . . . . |
$$ ----------------------------[/go]
White has no such capture ... the extension at seems best to me.
Re: which is a better move in this position?
Posted: Fri Dec 14, 2012 10:40 am
by Uberdude
I don't know the answer to that problem, though probably A is best as they both work and A asks white to make a heavy group in bad shape before capturing the side stones, whereas if white gets to nobi there his shape is better and the black group to the right could be attacked.
Also in that sort of shape sometimes the m2 clamp is the only move fast enough.
P.S. In topazg's diagram although black captures the outside stones which is great white does have a 1st line connection for later which he doesn't with the atari. If black is trying to make territory to the left side that could be quite significant.
Re: which is a better move in this position?
Posted: Fri Dec 14, 2012 3:48 pm
by Loons
My feeling was that 'a' is right, but now I'm not sure.
'a' gets closer to capturing the laddered stone.
$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . . 2 O X X X X . |
$$ . , . . X O X O O O . |
$$ . . 1 . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+
[go]$$Bc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . X . . . . . |
$$ . . . . X . X X X X . |
$$ . , . X X . X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X O O . . |
$$ . . . . . O O . . . . |
$$ ----------------------+[/go]
$$Bc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . X X . . . . . |
$$ . . . X . . X X X X . |
$$ . , . X X . X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X O O . . |
$$ . . . . . O O . . . . |
$$ ----------------------+
[go]$$Bc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . X X . . . . . |
$$ . . . X . . X X X X . |
$$ . , . X X . X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X O O . . |
$$ . . . . . O O . . . . |
$$ ----------------------+[/go]
Re: which is a better move in this position?
Posted: Sat Dec 15, 2012 1:30 pm
by speedchase
SoDesuNe wrote:It's B in this situation.
$$Bc White is forced to capture. Very good shape for Black, too.
$$ . . . . . . . . . . . . . . |
$$ . . . . , . . . . . , . . . |
$$ . . . . X . . . . . . . . . |
$$ . . . . . . . . . . . X . . |
$$ . . . . . . . . . . . . . . |
$$ . . . . . . . . . . . . . . |
$$ . . . . . . . . O X X X X . |
$$ . . . . , . 1 X O X O O O . |
$$ . 7 . . . . 5 O X O O . O . |
$$ . . . . . . 3 O X X 2 O . . |
$$ . . . . . . . . 6 4 . . . . |
$$ ----------------------------
[go]$$Bc
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . . . . . . . |
$$ . . . . . O X X X X . |
$$ . , . 1 X O X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------[/go]
For a while I thought that might be the preferable way to capture (on an otherwise empty board), because the side is bigger than either the corner or center.
$$Bc
$$ . . . . . . . . . . . |
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . 3 . . . . . |
$$ . . . . . O X X X X . |
$$ . , . 1 X O X O O O . |
$$ . . 2 . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------
[go]$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . 3 1 O X X X X . |
$$ . , . 2 X O X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]
What I don't get is if you're going to do this, why exchange the marked stone for ? Why not directly?
This line gets complicated. There is a white group cutting 3 black groups, only one of which is strong. I am having trouble seeing why capturing some white stones, connecting your groups, and leaving white with the only weak group isn't clearly right. Yet überdude also likes this move, so there has to be merit to this move that I'm not understanding. Can you explain it?
Re: which is a better move in this position?
Posted: Sat Dec 15, 2012 4:43 pm
by MMaestro
Depending on the rest of the board, the clamp can also be a viable option if you really don't want white to connect his left side stones to the right side.
Re: which is a better move in this position?
Posted: Sat Dec 15, 2012 5:41 pm
by gogameguru
This is an excellent question and it's worth spending some time pondering it.
@peppernut
peppernut wrote:
$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . 3 1 O X X X X . |
$$ . , . 2 X O X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+
[go]$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . 3 1 O X X X X . |
$$ . , . 2 X O X O O O . |
$$ . . . . O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]
What I don't get is if you're going to do this, why exchange the marked stone for ? Why not directly?
This line gets complicated. There is a white group cutting 3 black groups, only one of which is strong. I am having trouble seeing why capturing some white stones, connecting your groups, and leaving white with the only weak group isn't clearly right. Yet überdude also likes this move, so there has to be merit to this move that I'm not understanding. Can you explain it?
$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . 3 1 O X X X X . |
$$ . , . 2 X O X O O O . |
$$ . . . 4 O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+
[go]$$Wc
$$ . , . . . . . , . . . |
$$ . X . . . . . . . . . |
$$ . . . . . . . . X . . |
$$ . . . . . . . . . . . |
$$ . . . . . B . . . . . |
$$ . . . 3 1 O X X X X . |
$$ . , . 2 X O X O O O . |
$$ . . . 4 O X O O . O . |
$$ . . . . O X X . O . . |
$$ . . . . . . . . . . . |
$$ ----------------------+[/go]
In that case black plays here now and white doesn't have any particularly good move.
Playing the atari first wins hands down in this case. It's simply better technique.
That's because it creates better shape after capturing the stones, because makes white heavy before 'defending', because it slows white's future development and because it still creates miai. However, the answer to this question can change depending on the position. That's Go for you .
Here are some less settled (fictitious) positions to illustrate these points more clearly. Assume the ladder favors black in all cases.
Black has gained a little extra time to move here, because of the exchange of 1 for 2. If 6 is at 'e', black still plays 7.
[Updated and fixed mistake where I kept saying white instead of black. Thanks friendly editor ]
(note: 5 is better than 'a' for fighting here. Play 5 when you expect fighting in the center. Now 'b' isn't sente, but 'c' is sente instead and 'd' is sente in either case.)
Now 'a' and 'b' are miai for black and white's too thin to fight like this. Note that if white cuts at 'a' and black extends to 'b', white's cutting stones are captured. However, if black had played 'c' instead of 5 earlier, white would be able to escape with 'd' and black would be in trouble. This illustrates the subtle difference between those two moves. A lot of people think 5 looks less stylish, but it's the fighting move.
Sacrificing 1 costs black something and strengthens white's four stone group (which has to be considered because it diminishes the value of separating white in the first place). However, it can't be denied that white's groups have been separated and white will have to make four eyes instead of two now. Black's shape is worse now too.
This is a fighting variation which can be good if the global position supports this sort of strategy.
White can play a makeshift defense with 4, then play 6, and black practically collapses. All black can do now is try desperately to recover with a squeeze at 'a'. It might be good enough to keep playing for awhile, but it doesn't really work well enough. Black lost a lot here.
here and has a really good result.
seems best to me.
pretty well forces 
, now or in the next few moves.
is gote, it leaves behind 
, a nice yose.
directly?
]
, but...