# 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.

# Open formations

## L groups

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 , 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 , 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.

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 two-stage 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. (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.

## J groups

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

If 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. White a to c all lead to ko. Black can live with almost any move.

The weak carpenter's square is a carpenter's square without the connection at the corner of the shape. Black can make life by occupying the vital point at a. White can kill with almost any move.

That is, the fact that the 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 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.

## 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.

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.

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 and is alive. If Black plays first, he can achieve a seki at best.

White to play can make a life.