Preventing escape on the first line
In the early stages of learning Go, beginners will start to appreciate that preventing a surrounded opponent's group from escaping is usually not an easy matter. For example, how to prevent the opponent from escaping from the first line? Figuring this out may not be so easy, but fortunately, this is a situation that is easy to explain and understand. This article specifically explains how to prevent escape on the first line.
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Let's warm up with a really easy case. If this is superfluous to you, just skip to the next section.
At the corner, Black has only one eye - that of a straight three. We show that Black cannot escape to the outside and hence cannot avoid capture. In other words, Black is dead.
If tries to escape towards the right side, then easily blocks and Black has no way out. Similarly, if tries to escape, then blocks with a tiger's mouth, so Black has no way out.
One way the opponent can try to escape is via a hane on the first line.
Perhaps the first way that comes to mind is to continually pull back with , and so on.
At the end of the day, Black will run into the opposite corner of the board, and the opposite edge naturally stops the escape.
However, in real games, things are rarely so nice. Chances are, at a certain distance away, there are some Black stones, such as the stone in this diagram.
In this case, merely pulling back every time is not going to work. After , the corner Black group gets connected with the stone, so the corner Black group is suddenly alive again. Therefore White needs a better way of stopping Black from going out.
In this case, White can directly block at , which happens to be an atari on the line of Black stones. If connects, then defends against the cutting point. Now Black is totally surrounded. (And has lost some extra stones, as well.)
If tries to cut, then simply captures the Black stones, and it is game over for Black. (At least in the top left corner.)
Having understood the previous case, we now explore another case of the hane.
If makes the same atari as before, then Black can make a ko.
There is no way to avoid the ko, because and is the elementary first line capture technique. Further, may elect to use a net instead.
Pushing out from a descent
The hane was easy because it is possible to atari. Now we explore a harder case.
When Black pushes out from a descent, White can no longer atari, so it is more difficult to prevent the escape.
Timm: Black in the previous diagram (one point jump on the first line) is the “submissive” answer. This one is slightly more tricky.
Timm: White can also be more severe but the cut may be problematic, depending on the situation.
Here are two exercises on the methods for preventing escape on the first line.
Solutions to exercises
Note that a Black move at a is sente, in the sense that the next move at b makes two eyes. Therefore, this position should be treated like that with a descent at a.
A solution to Exercise 1 is to jump at . If attaches underneath, then and finishes the job. We leave it to the reader to figure out why at a is a mistake.
[Public Neophyte:] What's wrong with playing at a here?
Anon: Black gets to escape at b.
Joe?: But white can then capture the black stones by playing next to a, preventing two eyes. (Next, the two stones are captured by black, and a is played again.)
TheBigH: Then black can capture the new 'a' stone, and this connects the 2nd line stones to the ones crawling out on the first line. The problem is still how to prevent escape; assuming I've understood your question right.
Joe?: See here: http://eidogo.com/#1J3E67szL The false-eye shape can then be captured.
TheBigH: You said white plays next to 'a'. Your linked sgf does not have that variation. Like Slarty said, doing that would be an error. http://eidogo.com/#21jX7sgsW
Slarty: It's ok to play there first, because after , still works to prevent escape. It's nearly the same. The corner is dead as is. at b is a big mistake; black would ignore to play 3.
Observe that a Black move at a is an atari on three White stones, threatening to capture at b. Hence this position should be treated like the second kind of the first line hane.
A solution to Exercise 2 is to pull back at . This avoids the possibility of having to fight a ko.
- Beginner study section
- Life and Death
- Basics on kos