L+1 Group / Leg on the Long Side

Path: <= Life and Death =>

Sub-page of L1Group

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Sorry this page is still in development

A Long L+1 group is an L group with a leg at the long side.

A similar group exist with the leg at white+triangle (the short side) this is then the /legontheshortside

If there are legs at both sides it is the L+2 group.

Both L+1 groups lives or dies according to who has sente.

Don't confuse the Long L+1 group with this group which is the Long L group.

Table of contents
Sorry this page is still in development

Black to live

White to kill

Standard kill

Other kills

from the L+1 group / discussion

Hane on one side =

Hane on both sides

See also:

From corner shapes

L groups

Long L+1 group

Hane on one side

Hane on both sides

Weak leg

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

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Black to live

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

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White to kill

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Standard kill

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

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Other kills

What happens if White plays on Blacks vital point? (Just thinking about "Your opponent's good move is your good move" does that apply here as well? I think Black is dead as well but am i correct?

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from the L+1 group / discussion

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

aLegendWai: Qs ^^: How about if B plays at another 1-2, 2-2? Will B live? If so, is it better than the first solution?

Black will live when they play at 2-2, but has a chance to run into trouble, and in general will get fewer points in the corner. If white hanes right away, black must play the vital point, not block. If black blocks, white can play the vital point instead, turning the corner (through a ko if black plays 1-1 first) into Bent Four in the Corner. When Black backs down and plays the vital point, they end with two points fewer in the corner. So, the 1-2 is the main line.

~Coconuts (7k)

Please correct me if I've gotten any of this wrong =).

Bill: As shown above, by playing on the 1-2 point Black secures two eyes, defensible under attack.

on the 2-2 does not secure two eyes. White can continue to make seki or ko. (Here Black can still play at b to make ko, or he could have played at a, making ko that way.)

Best play depends on the circumstances, including ko threats. As a rule White can exploit Black's weaknessess after . In this case, for instance, White can start with , forcing . Black makes two eyes, but loses two points vs. playing one the 1-2 initially.

aLegendWai: In fact, it seems playing at either 1-2 point, or 2-2 point is alive in L+1 group.

Bill: See my later reply, above. Seki is life, but....

Generally speaking (not just limited to this case), when we decide which is the best move, what factors do we need to consider?

Any others?

Chris Hayashida: Edge hane aren't alive.

After , Black is dead. a and b are miai.

Chris Hayashida: Again, after , a and b are miai. Black is dead. Edge hanes don't make life.

aLegendWai: Thanks for telling.

zinger: Can white kill black regardless of the marked stone with the 2-1 placement?

unkx80: Well, depends on whether Black can get the hane at a in sente.

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Hane on one side =

The extra hane gives a sense of security.

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

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

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Hane on both sides

With a hane on both sides is alive if it has an external liberty. However, when the group has no external liberties, White can turn it into a ten-thousand year ko.

The key tesuji here is .

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

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

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

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

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.

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From corner shapes

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L groups

As it is, this is the L group. (The internal area is 2 by 3 points.) It is dead as it stands.

If white+square is Black, then it is a Short L+1 group, and white can kill it, or black can live.

Also if white+triangle is Black, then it is a long L+1 group?, and white can kill it, or black can live.

If both white+triangle and white+square are Black, then it is a L+2 group, and it is alive as it stands.

if both white+triangle and white+square are Black and square is White, then it is a L+2 group with descent, 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

A Long L+1 group is an L group with a legat the long side.

A similar group exist with the leg at black+triangle (the other side) this is then the /legontheshortside

If there are legs at both sides it is the L+2 group.

Both L+1 groups lives or dies according to who has sente.

Don't confuse this group with the Long L group.

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Long L+1 group

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

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

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

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Hane on one side

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

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

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

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Hane on both sides

The two hane stones give some degree of security.

The attachment at leads to ko.

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Weak leg

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