Common Corner Shapes

PageType: Path     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 overview of many of the corner shapes commonly encountered, and some shapes that are not so common, just because they are to be avoided.

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

This a only a list of the Common Corner Shapes for a more exhaustive list see Corner Shapes.


Table of contents Table of diagrams
[L group]
[L+1 group]
[L+1 group]
[L+2 group]
[Long L group]
[Tripod group]
[J Group]
[Carpenter's Square]
[Weak carpenter's square]
[Hovercraft]
[Bent Four in the corner]
[Bent four in the corner is dead]
[Rectangular six in the corner]
[Walkie Talkie Seven]
[Rectangular eight 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

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.

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 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 alive unless White also has a descent at a.


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 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.


Other open formations


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


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.


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.


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).


Eight spaces

In a rectangular eight in the corner 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.


Second line

{>Five Stones on the Second Line in the Corner] 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, the Five Stones on the Third Line in the Corner has more eyespace. If White plays first, the group can live unconditionally, while if Black plays first, a seki or ko may be possible.


See also:


Common Corner Shapes last edited by 202.156.180.188 on February 17, 2014 - 16:26
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