L+1 group

Path: LifeAndDeath   · Prev: LGroup   · Next: L2Group
  Difficulty: Intermediate   Keywords: Life & Death

An L+1 group is an L group with a leg. The leg can be at the short side or the long side of the L shape. In both cases the group lives or dies according to who has sente.

Table of contents


First L+1 group

[Diagram]

First L+1 group

The first L+1 group lives or dies according to who has sente.

[Diagram]

Black lives

Black can live by playing on the 1-2 point as shown.

[Diagram]

White kills

White can kill by playing hane at W1. This reduces the shape to the standard L group, which we already know is dead.


First L+1 group, hane on one side

[Diagram]

First L+1 group, hane on one side

The extra hane gives a sense of security.

[Diagram]

White cannot kill this way

The throw-in at W1 no longer works: B2 jumps and lives. If W3 makes a placement, B4 connects, and White cannot connect at a due to shortage of liberties, otherwise Black captures three to make an eye.

[Diagram]

White kills

However, White can kill by the hane at W1 followed by the placement at W3. B4 tries to live, but W5 forces B6, so W7 makes a throw in and kills. Note the importance of the white+circle stone.


First L+1 group, hane on both sides

[Diagram]

First L+1 group, hane on both sides

For hundreds of years or even thousands of years, the first L+1 group with hane on both sides is thought to be alive. However, when the group has no external liberties, White can turn it into a ten-thousand year ko.

[Diagram]

Main line

The key tesuji here is W3.

[Diagram]

Main line

The best moves by both players lead to a ten-thousand year ko.

[Diagram]

Main line

Black can also get a multi step ko (for white) sequence, which should be better than ten-thousand year ko

[Diagram]

Main line

white must first win this ko in the corner...

[Diagram]

Main line

Black can get rid of ko threats before continuing. If white wants to continue, he must play yet another ko to force the atari.

[Diagram]

Main line

Only now does the real ko for the life of the corner start. Black usually should be able to win this or receive ample compensation elsewhere in the steps white took.


Second L+1 group

[Diagram]

Second L+1 group

If the leg is on the other side, again the position depends on who has sente.

[Diagram]

Black lives

Now the 2-2 point is the vital point for Black.

[Diagram]

White kills

Again, reducing Black to a basic L group by a hane, kills the corner.


Second L+1-group, hane one side

[Diagram]

Second L+1-group, hane one side

The hane at black+circle may give some help in living.

[Diagram]

White cannot kill this way

The throw-in at W1 doesn't work anymore. Black lives with B2: White can not connect at a because Black can capture three to make an eye.

[Diagram]

White kills

To kill, W1 can go straight to the 2-2 point. After W7, Black is dead. See the addendum of the rectangular six in the corner page. As before, the white+circle stone is important.


Second L+1-group, hane on both sides

[Diagram]

Problem

The two hane stones give some degree of security.

[Diagram]

Solution

The attachment at W1 leads to ko.


Second L+1 group, weak leg

[Diagram]

Second L+1 group

The second L+1 group with a weak leg is also unsettled. White can kill at a or Black can live by playing at a.


Something like an L + 1 group

[Diagram]

Third L+1 group

This group is somehow like an L + 1 group. a for black lives, b for white kills.


See also:


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This is a copy of the living page "L+1 group" at Sensei's Library.
(OC) 2009 the Authors, published under the OpenContent License V1.0.
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