Empty triangle

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    Keywords: Shape, Go term
[Diagram]

Empty triangle

Chinese: 空三角 (kong1 san1 jiao3)
Japanese: 空き三角 (akisankaku)
Korean: 빈삼각 (bin sam gak)

This shape is an empty triangle, empty referring to the unoccupied point at [circled point].

The empty triangle is bad, generally, being inefficient and prone to shortage of liberties. But there are also good empty triangles (see guzumi).

In contrast, the full triangle, with a White stone at [circled point], is good shape.

Beginners: Here's a page to help you spot the empty triangle and avoid it.

[Diagram]

Not an empty triangle

Additional Black stones, such as the legs of a, or b or c, give this shape different efficiency and shortage-of-liberties characteristics, and as such it is no longer called an empty triangle, although it may still be so-called stupid shape (gukei).

[Diagram]

Diamond

The presence of the BS stones in place mean that this is not an empty triangle either, but rather a diamond or ponnuki with an extra stone at BC, a common shape.


Empty triangle is also sometimes called the devil's shape (onigatachi), because it brings to mind the long nose of one kind of Japanese demon.


Examples

This first example, from professional play, offers a surprisingly large number of empty triangles.

[Diagram]

Gu Li (W) - Qiu Jun, 2005 Agon-Kiriyama Cup Final

The capture of BC leaves an empty triangle -- in fact, two empty triangles,-- around the vacated point. Since it is a capture and threatens another capture, it may be a good play, but it does form empty triangles.

[Diagram]

Gu Li (W) - Qiu Jun (ii)

Next, B2 plays atari, catching the WC stones in a connect and die. This illustrates the liberty problem with the empty triangle (too few liberties per stone played). W3 takes BC, forming another empty triangle, and B4 takes the WC stones, incidentally forming one more empty triangle.

[Diagram]

Gu Li (W) - Qiu Jun (iii)

Now W5 forces B6, which forms another empty triangle. (At this point, who cares?)

[Diagram]

Gu Li (W) - Qiu Jun (iv)

A little later W5 cuts, but forms another empty triangle. W7 forces B8, which forms another empty triangle. B10 is atari, but forms yet another empty triangle.

[Diagram]

Gu Li (W) - Qiu Jun (v)

W1 connects, but forms another empty triangle. Now B2 forces W3, taking advantage of the liberty problem. B4 forces W5, which forms yet another empty triangle. After B6 secures the corner, W7 ensures the capture of the BC stones, taking advantage of the liberty problem. Finally, B8 makes an important connection, but forms an empty triangle in the process.

This comedy of empty triangles (11 in 24 moves!) illustrates some of the problems with empty triangles, as well as the professionals' willingness to put up with those problems if the circumstances warrant.


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This is a copy of the living page "Empty triangle" at Sensei's Library.
(OC) 2007 the Authors, published under the OpenContent License V1.0.
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