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|
When Black has a stone at , 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 , then it is an L+2 group, and it is alive as it stands.
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.
This is the Tripod group with extra leg, which can be formed when the - 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.
If black has a stone at b, this group is unconditionally alive.
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 - 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 - 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 being a black stone and b and c being White stones, is unconditionally alive.
This is called the straight J group, leading to ko if White to play. See J group for details.
The black formation in this diagram is the carpenter's square. White a to c all lead to ko. Black can live with almost any move.
The position where is empty is also included on the weak carpenter's square page. It is in unsettled status.
For other related shapes, see Shapes related to the carpenter's square page.
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 to play can make a life.
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
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 fewer than two outside liberties.
If is White and Black's lower group has no outside liberties, then the corner is unsettled and a is the vital point.
If is White and Black's lower group has at least one outside liberty, then Black is alive with both groups and 3 points of territory.
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?
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 where white needs one approach move; and with two, the group is alive as it stands.
If in the Rectangular six in the corner the corner point is White, the shape is a bit weaker, although black to move still lives with both groups and 5 points of territory by playing at b. What white can do depends on the number of outside liberties; it may be killable. For example, if the short side has at least one outside liberty and the long side has no outside liberties, then white to move kills by playing at a.
The non-standard SL name for this shapeis claw hammer six. 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 becomes an auto atari.
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 , although a is preferred because it leaves no ko threats.
If it is white's turn, the walkie talkie seven shape can be turned into a throw-in ko by playing at a. 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 ten thousand year ko. Unless White is komaster, Black will normally play elsewhere after the exchange of b and c, as White only threatens a ten thousand 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.
Black can easily live with 7 points of territory by playing at a. (Other defenses are more susceptible to White's ko threats.)
This position also turns into a seki if White plays a
See also :
In the position on the left the points a and b are miai
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.