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GiveMeLiberties

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Atari

 

Two liberties
Path: GiveMeLiberties   · Prev: Liberty   · Next: ShortageOfLiberties
  Difficulty: Introductory   Keywords: Tactics

In my games, I've noticed that nearly as important as atari is when a group has just two liberties. What kind of liberties they are determines whether they're safe.

When a group has just two liberties, unless both are eyes, it is one move away from being in Atari. In all of the below discussion, I assume that the groups don't have two eyes.

Make sure that your group can be saved, even if either liberty is taken.

Basic Example

[Diagram]
Can Black save this group?

This group has two liberties, a in the northwest and b in the south.


[Diagram]
Attack from northwest

Black can defend an attack from the northwest...


[Diagram]
Attack from south

... but not from the south. The black stones die, because if Black tries to escape with B2, White can capture with W3.




More Examples

Three examples are inspired by my own games:

[Diagram]
White is dead

The WC stones are dead. My kosumi was half-cut by the BS stone, and cut by B1. If White responds at a, Black will kill at b.


[Diagram]
White is dead

After B1, the white stones are dead. If White plays at a, Black will capture at b. (See shunt.)


[Diagram]
Is a a good move?

W moves at W1. What happens if Black moves at a?


[Diagram]
Black dies

Black loses eight pieces, because he lacks liberties.




Ladders and Nets

Many situations are related to having just two liberties.

[Diagram]
Ladder example

In a ladder, an attacker repeatedly reduces a group of stones from two liberties to one liberty.


[Diagram]
corner

A simple net keeps the number of liberties to two or less.

White has two liberties. If white moves to either a position, black will reduce white's liberties by moving to the nearest b position.




Double atari

[Diagram]
corner

A double atari can occur when two groups with just two liberties share a liberty that's not an eye.




Ko threats

[Diagram]
Ko threat

Every group with just two liberties (not both eyes) can be used as a ko threat.




Auto-atari

[Diagram]
Auto-atari, part 1

Auto-atari can only happen when your group had two liberties, you move into one liberty, and you gain no more liberties. In this diagram, I chased after WC, only to discover...


[Diagram]
Auto-atari, part 2

... that I hadn't counted my liberties.


[Diagram]
Oi otoshi

Same shape, different order.



A snapback is a specific kind of auto-atari.


See also:


Alex Weldon: Even three is not enough, quite often.

[Diagram]
Geta

Here, White can be captured in geta with a Black move at a.

In fact, see Five liberties for tactical stability.



Path: GiveMeLiberties   · Prev: Liberty   · Next: ShortageOfLiberties
This is a copy of the living page "Two liberties" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.