gostudent wrote:
I am under the impression that three-space extension is often bad, because of the potential invasion of (c) or (d) (and in this case, that would also be corner approach). For the top right corner, I am not afraid because I have entering 3-3 as emergency option, but here I am less sure.
What should white do if black invades at (c) or (d)? Thanks.
First of all, you should realize that while 10 is a 3 space extension, that is not its primary purpose; that is to undermine the 4th line black stone of 9.
Next is to appreciate the big difference between a 3 space extension from 3rd to 4th line and one from 3rd to 3rd or 4th to 4th. The former has much better connectivity, as shown in the diagram below. In the latter you can usually connect by attaching and sacrificing a stone, but that is costly.
- Click Here To Show Diagram Code
[go]$$B
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . 8 6 . . . . . . . 8 6 . . . . |
$$ | . . . O 5 2 3 . . , . . . 5 2 3 . . . |
$$ | . . . . 7 1 4 O . . . . O 7 1 4 O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]
The next important thing is the presence of the opponents stones, particularly as checking extensions. These make the invasion more difficult to deal with as they are a friendly stone for your opponent to connect to and mean you can't extend to make eyespace on the side.
So perhaps a better "proverb" would be:
Quote:
A 3 space extension on the 3rd line has poor connectivity, so if you want to be connected you should only do it if you have a good plan to deal with the invasion.
Let's look at some examples:
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . X . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . 2 . . |
$$ . . . . . . . . |
$$ . . . . , 1 . . |
$$ . . . . . . . . |
$$ . . . . . 4 . . |
$$ . . . . . . . . |
$$ . . . . . 3 . . |
$$ . . . . . . . . |
$$ . . . . , X . . |
$$ . . . X . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
Here white is in black's sphere of influence with a strong shimari below (black already has checking extensions both sides), so a 3 space extension is not a good idea as white doesn't want to make 2 groups but stay connected and settle his one stone. So a 2 space extension is better.
However here black has just a 4-4 below, so white's jump out is pretty much sente*, which then allows the kosumi of 7 to more-or-less connect (black could then play
a which threatens to push at
b and cut with black having the tesuji of
c to make miai to connect above or below, so it is honte for white to answer
a at
b.
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . X . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . 2 . . |
$$ . . . . . . . . |
$$ . . . . , 1 . . |
$$ . . . . 7 . . . |
$$ . . . . b 4 c . |
$$ . . . . . . . . |
$$ . . . 5 . 3 . . |
$$ . . . . . . . . |
$$ . . . . X . a . |
$$ . . 6 . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
*If black doesn't answer white is happy to build influence on the lower side and later could save 1 or use its aji with e.g.
z.
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . X . . . |
$$ . . . . . . . . |
$$ . . . . . z . . |
$$ . . . . . . . . |
$$ . . . . . 2 . . |
$$ . . . . . . . . |
$$ . . . . , 1 . . |
$$ . . . . 6 . . . |
$$ . . . . . 4 . . |
$$ . . . . . . . . |
$$ . . . 5 . 3 . . |
$$ . . . . . . . . |
$$ . a 7 . X . b . |
$$ . 9 8 0 . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
Sometimes we don't mind being disconnected as we have space to extend. Here white extends 3 spaces with 3 and if black invades just calmly makes a 2 space extension to settle the lower stone (note this is not a 3 space because we don't want to get split now, like above). Black might then follow up on 1 with
a/b and white might continue there, or more likely at this stage of the opening, tenuki to a bigger area.
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . 2 . . . . . |
$$ . . . . X . . . |
$$ . . . . . a . . |
$$ . . . . b 1 . . |
$$ . . . . . . . . |
$$ . . . . . 4 . . |
$$ . . . . . . . . |
$$ . . . . , 3 . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . 5 . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . , X . . |
$$ . . . X . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
As a variation on the above, if black doesn't have a shimari at the bottom right white could think about making a 2nd 3 space (2 is still good and simple) though it could get rather crazy complicated. Simple is for black to answer with shimari and then white defends the gap.
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . 2 . . . . . |
$$ . . . . X . . . |
$$ . . . . . . . . |
$$ . . . . . 1 . . |
$$ . . . . . . . . |
$$ . . . . . 4 . . |
$$ . . . . . . . . |
$$ . . . . , 3 . . |
$$ . . . . . . . . |
$$ . . . . 7 . . . |
$$ . . . . . . . . |
$$ . . . . . 5 . . |
$$ . . . . . . . . |
$$ . . . 6 , X . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
Or things could go crazy. (I would only recommend doing this when you are dan level.)
- Click Here To Show Diagram Code
[go]$$W
$$ ----------------+
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ . . 2 . . . . . |
$$ . . . . X . . . |
$$ . . . . . . . . |
$$ . . . . . 1 . . |
$$ . . . . . . . . |
$$ . . . . . 4 . . |
$$ . . . . . . . . |
$$ . . . . , 3 . . |
$$ . . . . . . . . |
$$ . . . . . 6 . . |
$$ . . . . . . . . |
$$ . . . . . 5 . . |
$$ . . . . . . . . |
$$ . . . . 7 X . . |
$$ . . . . 8 9 . . |
$$ . . . . . . . . |
$$ . . . . . . . . |
$$ ----------------+[/go]
As you say, another way to deal with the invasion is sacrificing one stone and using it to jump into 3-3. Now in your board if black invaded at the top white should probably attach on top as it's a 3rd to 4th line 2 space extension with good connectivity, but if k16 was at k17 then 3-3 makes more sense.
So back to your question, my first thought is to attach and stay connected. Black can wedge with 13 because he has the ladder (to top right if white ataris from below and connects to left). Black gets the corner, but white gets a strong wall that contributes to his growing left side moyo, and also k4 has become rather weak. I prefer white as black is ruining his own moyo prospects with giving white such thickness.
- Click Here To Show Diagram Code
[go]$$Bm11
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . . . . |
$$ | . . . O . . . . . O . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . d . . . . . . . . . . . . . |
$$ | . . . . 4 . . . . . . . . . . . . . . |
$$ | . b 8 O 3 2 6 . . X . . . . . , . . . |
$$ | . 0 9 7 5 1 . O . . . . . . . X . . . |
$$ | . a . . . . c . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
Another idea is to jump to the key point that black would like to have got and start a big running fight. But now white wants to play at
a and
b, so while might be able to play
b and then cut at the waist if black
a as black doesn't have the ladder, this is a complicated fight so I would recommend the simple attach of before.
- Click Here To Show Diagram Code
[go]$$Bm11
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . O . . . . . |
$$ | . . . O . . . . . O . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . a . . . . . . . . . . . . . . . |
$$ | . . . . . 5 . b . . . . . . . . . . . |
$$ | . . . 4 . . . . . . . . . . . . . . . |
$$ | . . . . . 3 . 2 . . . . . . . . . . . |
$$ | . . . O . . . . . X . . . . . , . . . |
$$ | . . . . . 1 . O . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]