Corner shapes

    Keywords: Life & Death, Shape

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

On this page we give a comprehensive overview of all the various corner shapes commonly encountered, not only of groups where the question is, are they dead or alive, but also shapes that address whether they are alive with territory or only alive in seki.

Feel free to add links to other common corner shapes. If you are unable to make diagrams or give a nice introduction, add it under unclassified.

This page is not for discussions or comments on individual shapes. Please add such discussion or comments to the linked pages. Moreover, please provide comments or corrections 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.

Recently there were some comments about the exhaustive nature of this page therefore there is now a page Common Corner Shapes - in real games the open corner shapes presented in the first part of the page are much more likely to occur than most of the closed corner shapes presented in the second part.


Table of contents

Open formations

L groups

[Diagram]
L group  

As it is, this is the L group. (The internal area is 2 by 3 points.) It is dead as it stands.

When Black has a stone at black+circle, then it is a L+1 group (specifically, an L group with a leg on the long side). The group is unsettled; namely, white can kill it, or black can live.

When Black has a stone at black+circle, then it is a different kind of L+1 group (specifically, an L group with a leg on the short side). The group is also unsettled; namely, white can kill it, or black can live.

If Black has two stones at black+circle, then it is an L+2 group, and it is alive as it stands.

However, if there is also a White stone at a, then it is an L+2 group with descent. In this case, 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


Tripod groups

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.

This is the Tripod group with extra leg, which can be formed when the black+circle-white+circle exchange is made to an existing tripod group. Beginners might think that it is alive because it is bigger and therefore looks stronger than the normal tripod group; however, it is weaker, as White can get a ko after the sequence White a , Black b, White c.


J groups

[Diagram]
J Group  

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 Pig's 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, and should be studied together with the J-group.


This is the Short J group, which is often formed when White tries to attack the tripod group through the white+circle-black+circle exchange. It is alive as it stands but becomes unsettled if there is a White stone around a.


This is the Short J group with extra leg, which is typically the result of playing out the black+circle-white+circle exchange after forming the Short J group. It is also known by its Chinese name "little pig's snout." As in the case of the Tripod group with extra leg, this group is weaker because White can get a ko after playing at a.

Note that a variant of this group, with white+square being a black stone and b and c being White stones, is unconditionally alive.


Carpenter's Squares

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 carpenter's square page.


Second line

This group lives or dies according to 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 unconditionally, while if Black plays first, a seki or ko may be possible.


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 zero or one outside liberties, 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, the group is unsettled, and 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 outright, while with one outside liberty it can be turned into a ko; and with two, the group is alive as it stands.

[Diagram]
Comb formation in the corner?  

If in the Rectangular six in the corner the corner point white+cross is White it is a Comb formation in the corner? this shape is a bit weaker but again depending on the number of outside liberties, it is alive or dead.

[Diagram]
Gun six  

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


[Diagram]
No name yet  

This shape has no name yet. If there are no outside liberties, White can turn it into a seki by playing at a which Black needs to answer at b. After which White c turns it in a seki, Black at square becomes an auto atari


[Diagram]
Big P  

This looks like 6 points of territory for Black; however, after White a, Black can only get a seki or a ko. Black can turn it into 5 points of solid territory by playing a or either square, although a is preferred because it leaves no ko threats.


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 after the exchange of b and c, 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 a Black stone, 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.

This position also turns into a seki if White plays a


See also :

Ten spaces

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


This is another corner group 10 spaces, that White can turn into a seki. After White a b and c are miai see staircase ten for how.


Eleven or more spaces

[Diagram]
Twelve points of territory  

(As far as I know) All closed corner shapes with eleven or more spaces without cutting points and without enemy stones inside them are alive with territory as they stand.

In the position on the left the points a and b are miai

For very big corners it might be possible for White to live inside the corner. but even in that case she cannot reduce Black to a seki


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


See also


Corner shapes last edited by 202.156.180.188 on February 17, 2014 - 16:26
RecentChanges · StartingPoints · About
Edit page ·Search · Related · Page info · Latest diff
[Welcome to Sensei's Library!]
RecentChanges
StartingPoints
About
RandomPage
Search position
Page history
Latest page diff
Partner sites:
Go Teaching Ladder
Goproblems.com
Login / Prefs
Tools
Sensei's Library