Common Corner Shapes
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.
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. (Note how it is "smaller" than the L-group, which is dead, but it is less surrounded.)
Black needs to remember the correct reply to three white attacks. See probe for an example of how it may form.
If black has a stone at b, this group is alive.
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 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
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 less than two outside liberties.
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.
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).
Black can kill with a move at a, while White can live with the same move.
Shorter groups are dead
Longer groups are alive
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 and is alive. If Black plays first, he can achieve a seki at best.