Corner shapes

    Keywords: Life & Death, Shape

There are a lot of shapes in the corner which occur regularly. To save yourself the time of reading out their status every time, it is useful to study these basic shapes and remember what their status is.

On this page we want to give a comprehensive overview of all common different corner shapes. Not only of groups where the question is if they are death or alive, but also shapes where the question is are they alive with territory or are they only alive in seki

Feel free add links to other common corner shapes. if you feel unable to make diagrams or give an nice introduction add it under unclassified.

This page is not for discussions and comments on individual shapes add them to the page where this page links to. (But do comment if the introduction is unclear or just wrong)

An overview of basic shapes outside the corner can be found on the life and Death page


Table of contents Table of diagrams
[L-groups]
The [long L group]
[Tripod group]
[J Group]
[Hovercraft]
[Carpenter's Square]
[Weak carpenter's square]
[Bent Four in the corner]
[Bent four in the corner is dead]
[Twisted four in the corner]
[Twisted four]
[Bulky five]
[Rectangular six in the corner]
[Gun six]
[Walkie Talkie Seven]
[Bulky Seven in the Corner]
[Rectangular eight in the corner]
[Gun Eight]
[Bulky Eight in the Corner]
[walkie talkie eight in the corner]
[Square nine in the corner]
no name yet
[Bulky ten in the corner]
[Five Stones on the Second Line in the Corner]
[Bent five on the second line in the corner|Five Stones on the Second Line in the Corner#diag7]
[Bent five on the second line in the corner|Five Stones on the Second Line in the Corner#toc2]
[Five Stones on the Third Line in the Corner]

Open formations

As it is, this is the L group, and it is dead as it stands.

If one (but not both) white+circle is Black, then it is a L+1 group, and white can kill it, or black can live.

If both white+circle are Black, then it is a L+2 group, and it is alive as it stands.

if both white+circle are Black and square is White, then it is a L+2 group with descent, white can make a approach ko or seki.


Long L group (the internal area is 2 by 4 points, whereas in the L group it is 2 by 3 points.)

If this group has no outside liberties, white can create a ten thousand year ko. If it has at least one outside liberty, white can make seki.

Note: If both legs are extended to the sides it is a Rectangular Eight In The Corner


The Black group in this diagram is 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.


The black shape in the diagram is the basic J group. It has the same status as an L+1 group: it lives or dies according to sente. This basic shape is known in China as the Big Pigs Snout.

If black has a stone at b, this group is unconditionally alive.

If the black stone black+circle is at c instead, it is called a "straight J group", and the best white can get by playing first is a ko.

If white+circle is replaced with a Black stone, the resulting group is called a J+1 group, which is unconditionally alive unless White also has a descent at a.


This formation is often formed by a 3-3 point invasion. It is unconditionally alive as it stands. If White has a stone at a, however, the group can then be killed.


The black formation in this diagram is the carpenter's square. The vital point is a: Black can play there to live. White can play there to turn the corner into ko.


The weak carpenter's square is a carpenter's square without the connection at the corner of the shape. The vital point is the same, but this time White can kill the corner by playing at a.

That is, the fact that the white+circle stone here is white, rather than Black, changes a the status of the group from Black can live, White can make a ko to unsettled status.

The position where white+circle is empty is also included on the weak carpenters square page.


Closed formations

This section only covers those shapes where the fact that they are in the corner is important. For other shapes, whose status is the same whether they are in the corner, on the edge or in the center, see Eye Shapes

Four spaces

The black formation in this diagram is the Bent Four in the corner. The vital point is a: Black can play there to live unconditionally, while White can play there to get a ko if the group has less than two outside liberties.


(Advanced topic)

Under Japanese rules, a group which is surrounded by one or more live enemy groups and whose eyeshape can be reduced to a bent four in the corner, is dead.


A twisted four in the corner is not the same as the normal twisted four.

If there are none or one outside liberty, White can turn this position into a ko.

If there are two or more outside liberties, Black is alive with three points of territory.


This is a normal twisted four but placed in the corner, it is alive and gives Black four points of territory

If black+circle is White a becomes the vital point


Five spaces

The bulky five in the corner lives and dies depending on who can play a. It is no different from the normal bulky five. A black play on b is a mistake. Why make a Twisted four in the corner when you can make a living group with a?


Six spaces

For the Rectangular six in the corner life and death or ko it all depends on the number of outside liberties. With no outside liberties, it can be killed, with one outside liberty it can be turned in to ko, and with two it is alive as it stands. (some skill is also required)

This shape is called the gun six If there are no outside liberties, this 6 points large eyeshape can be turned into seki. Any of the three marked points accomplishes this result.


Seven spaces

If it is white's turn the walkie talkie seven shape can be turned into a throw-in ko. White has two occasions to turn it into seki. The more outside liberties, the less likely the ko will be played (and thus the more likely White makes it seki in the end).


In the Bulky Seven in the Corner a is the vital point If White plays first, this shape becomes a seki or a 10,000 year ko. Unless White is komaster, Black will normally play elsewhere, as White only threatens a 10,000 year ko, and the best Black can do is seki, while in the original position Black could live with 6 points of territory.

A Black play at a turns this shape into 6 points of territory.


Eight spaces

Black can easily live with 7 points of territory by playing any of the points a.

For White it is more complex, its value and play depends upon the ko threat situation. If White is komaster she can often make seki with sente.


When there are no outside liberties, this eight-point large eye shape can be turned into seki or ko. In this position a is the vital point.


In the corner even an eight point large eye space is not enough to guarantee territory. White can make a seki or ko inside Black's corner


This is a walkie talkie eight in the corner if it is White's turn he can turn this group into a seki in gote. Black can turn it into seven points of territory by playing on any of the points a.

white+circle is the important point if it is Black the group would be alive with 8 points of territory


Nine spaces

When there are no outside liberties, White can turn this into sente seki. The vital point (obviously) is a.

[Diagram]

no name yet

This position also turns into a seki if White plays a


Ten spaces

[Diagram]

Bulky ten in the corner?

Even this 10 spaces big group is not alive with territory if White plays at a it becomes a seki or a ko


Second line

This group lives or dies according sente

Black can kill with a move at a, while White can live with the same move.

Shorter groups are dead

Longer groups are alive

White can play at a to live, black can play there to kill.

White should play at a to live, other moves will allow black to kill. Black can kill with a, or with either hane on the first line


Third line

When compared to the case of five stones on the second line in the corner, this White group has more eyespace. If White plays first, the group can live, while if Black plays first, a seki or ko may be possible.


Unclassified

Here you can add links to other pages without having to wonder under which group it belongs, how to make a diagram or wonder about writing an introduction. Or when you are just busy.

Or just becaus you are unsure of its status or if it is alive with territory or alive in seki.


See also:


This is a copy of the living page "Corner shapes" at Sensei's Library.
(OC) 2009 the Authors, published under the OpenContent License V1.0.
[Welcome to Sensei's Library!]
StartingPoints
ReferenceSection
About