Rectangular six

    Keywords: Life & Death

Chinese: 板六 (bǎn lił)
Japanese: 板六 (ita roku)
Korean: 판륙

A group with a big eye with the shape of a rectangular six, is alive except for rectangular six in the corner.

Table of contents

Rectangular six without cutting points

[Diagram]
Rectangular six  

Here, the eyespace is at the side, but in the center the implications are the same. The vital points are a and b and they are miai, as shown in the following diagrams.

[Diagram]
Main line  

W2 makes miai of a and b to live with six points.

[Diagram]
Main line  

For instance, if B3, W4 makes two eyes.

[Diagram]
Variation  

W2 makes miai of a and b to live with six points.

[Diagram]
Two moves in a row  

If White tenukis, playing W4 elsewhere, White is still alive but now lives in seki: Black can at most almost fill with a bent four. However, this seki is not valid for rectangular six in the corner.



Rectangular six with cutting points

[Diagram]
Rectangular six with cutting points  

There are two cutting points (induced by black+circle) in the otherwise ordinary looking rectangular six. Notice that one of the two chains has no outside liberties at all.

The status of this group is actually unsettled. If Black plays first, White can be killed. The Chinese calls this [ext] 断头板六 (literally, "decapitated" rectangular six).

[Diagram]
Rectangular six with cutting points  

Black can kill by playing the placement at B1 and then cutting at B3. Owing to shortage of liberties, a White move at a would be self-atari, so White can no longer form two eyes.

[Diagram]
Rectangular six with cutting points  

On the other hand, if the rectangular six group has two cutting points as shown, then it is still alive. The comb formation is essentially a rectangular six with two cutting points of this form. Life and death can be so strange.


See also


Rectangular six last edited by MrTenuki on June 13, 2011 - 23:00
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