Capture three to make an eye

  Difficulty: Beginner   Keywords: Life & Death, Proverb

The proverb capture three to make an eye refers to capturing three stones in a closed corridor, which normally ensures an eye if the corridor has no cutting points.

Table of contents

Capturing three stones suffices to make an eye

An example at the edge of the board.

[Diagram]
Capture three to make an eye  

When White captures at W1 ...

[Diagram]
Capture three to make an eye  

...even when Black throws in with B2, White can make a second eye with W3.



This works away from the edge, too.

[Diagram]
Capture three to make an eye  

Capturing three White stones at B1 makes an eye too, so Black lives.


Exceptions

However, this proverb has exceptions too, such as the following, where the corridor has a cutting point.

[Diagram]
Exception  

In this case, despite capturing three Black stones at W1...

[Diagram]
Exception  

... B2 kills. Since a and b are miai, White dies.



Here is another counter-example, where the corridor has already been cut. Such counter-examples can also be found away from the side.

[Diagram]
Exception  

If Black captures the three stones with B1, then...

[Diagram]
Exception  

... W2 recaptures. Because of W2 and white+circle the eye around a is a false eye.


Heuristic

A possible heuristic to see whether the "capture three to make an eye" proverb applies is to look at the position immediately after capturing. In each of the four cases below, we see whether we can form an Black eye at either the a points. If White can occupy all the b points after Black's capture, then Black has no eye here.

[Diagram]
Heuristic for corner.  
[Diagram]
Heuristic for side.  
[Diagram]
Heuristic for side.  
[Diagram]
Heuristic for center.  
[Diagram]
Heuristic for center.  

See also

Notes and discussion

PJT 2019-12-16: The Korean(?) text 석점을 잡으면 한 눈을 만들 수 있다 was substituted for the title of the first section. If this means the same, we might put it in a CJK box; if it uses a colourful image, it would be nice to know; if it was vandalism, we should lose it.


Capture three to make an eye last edited by PJTraill on December 16, 2019 - 21:47
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