Tripod Group

Path: LifeAndDeath   · Prev: LongLGroup   · Next: JGroups
  Difficulty: Beginner   Keywords: Life & Death, Ko

Table of contents

The tripod group

[Diagram]

Tripod group

The black group in this diagram is called the tripod group. It is one of the smallest shapes in the corner that is alive as it stands. Black needs to remember the correct reply to three white attacks. See probe for an example of how it may form.

[Diagram]

First attack

This is the first attack. After B2, Black still has a live shape in the corner.

[Diagram]

Second attack

This is the second attack. After B2, Black lives.

[Diagram]

Third attack

This is the third attack. Black can live with B2.



First attack

[Diagram]

First attack

The first attack at W1 is repeated here for convenience.

[Diagram]

First attack

If W1 blocks, then B2 lives.

[Diagram]

First attack

If W1 makes a placement here, then B2 hanes. W3 and B4 are miai for life.

[Diagram]

First attack

The descent at W1 is answered by B2 as well.

[Diagram]

First attack

W1 and W3 is probably the strongest attack, threatening a ko. The throw-in at B4 is neccessary for life. The result is oshitsubushi.

[Diagram]

First attack

If W5 captures, then B6 and B8 lives by oshitsubushi as well.

[Diagram]

Mistake

B4 here would be a mistake, because W5 turns the whole group into a ko.

[Diagram]

Mistake

The descent at B2 is a mistake, because W3 is the eye-stealing tesuji, making a placement and aiming at setting up a snapback at a. Black is dead.



Second attack

[Diagram]

Second attack

The second attack at W1 is repeated here for convenience.

[Diagram]

Second attack

The second attack is so much easier.

[Diagram]

Second attack

Note that W1 is sort of sente. For unconditional life, B2 is neccessary.

[Diagram]

Tenuki

If B2 plays elsewhere, then W3 and W5 can create a ko.

[Diagram]

Reference

B2 here lives too, but it appears not to be the recommended move. Probably the reason is that a White descent at a becomes a definite sente, in the sense that White will get a unconditional kill if Black plays elsewhere. See 1-2 point problem 1 for the reason.

[Diagram]

Reference

The crawl at B2 here may or may not be a good move, and depends heavily on whether the white+circle stone exists, and the White stones in the vicinity of white+circle. In this case, the clamp at W3 takes away all the eye space and kills. Therefore, in life-and-death problems, the main line always have B2 at W3.



Third attack

[Diagram]

Third attack

The third attack at W1 is repeated here for convenience.

[Diagram]

Third attack

W1 and W3 aims for either a ko or a bent four in the corner kill, but with the key move of B4, Black can live.

[Diagram]

Third attack

Subsequently, if W1, then B2 and B4 can lives by oshitsubushi.

[Diagram]

Third attack

Similarly, if W1 captures, then Black lives by oshitsubushi as well.

[Diagram]

Reference

B1 lives too, but depending on the ruleset used, may give White an infinite supply of ko-threats.

[Diagram]

Reference

White can aim for a ko with W1. To avoid a ko, B2 and B4 would be neccessary. The rest is pretty much a one lane road, with B10 living unconditionally by a double ko.



Surrounding stones

[Diagram]

Surrounding stones

Surrounding stones do matter for the status of the tripod group. For example, if there is a White stone at a or b, then the status becomes unsettled.

[Diagram]

Surrounding stones

In this case, when there is the white+circle stone, then W1 and W3 can kill. Black has no answer for W7.

[Diagram]

Surrounding stones

Again, for the case when white+circle is present, W1 can kill. W7 falsifies the eye on the side.



The tripod group with the extra leg

[Diagram]

Tripod group with extra leg

While the tripod group is unconditionally alive, Black should not make the exchange of B1 and W2.

[Diagram]

Tripod group with extra leg

The reason is that after the exchange, W1 and W3 turns the whole group into a ko. See tripod group with extra leg for more detailed discussion for this.



Practical application

[Diagram]

Application

This is a position from the final game of the 2000 German Championship, between Franz-Josef Dickhut (Black) and Christoph Gerlach (White). Black wanted to do something about the upper left corner.

[Diagram]

Invasion

So he invaded at B1. White can play W4 one point higher, but then Black has a cut at W4, which he can use to isolate the two white stones at the top. Either way Black creates a nice position.

[Diagram]

Two points smaller corner

From an endgame point of view, it is better for White to play like this diagram (1 replaces 8 above): Black will end up with two points less in the corner. However in the game White followed the previous diagram, probably because he didn't like the remaining weaknesses on the left side following this sequence at a.



See also


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This is a copy of the living page "Tripod Group" at Sensei's Library.
(OC) 2008 the Authors, published under the OpenContent License V1.0.
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