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Two Eyes
Path: LifeAndDeath   · Prev: Eyes   · Next: EyeSpace
Path: EyesCollection   · Prev: Eye   · Next: FalseEye

  Difficulty: Beginner   Keywords: Life & Death

To be safe from capture, a group of stones must have two eyes (or be able to make them in response to any threat). This is the primary way to make groups alive (the other, less desirable way is seki).

The basic rules of go state that when a group's last liberty is removed, the group is captured (removed from the board). It follows that, if a group has at least two liberties which cannot be removed, then the group cannot be killed and is alive. All subtleties aside, such an unremovable liberty is what we call an eye.

[Diagram]
Diag.: Example

Look at the circled points. A White stone placed on any of them would be disconnected from her own stones and would have no liberties. Both Black chains would still have the other circled point as a liberty. Such a White move would thus be illegal. Neither of the two circled points can be occupied without the other. In conclusion, the circled points are two unremovable liberties of the Black group, or two eyes and it is impossible to remove the Black group from the board.




Authors

  • Morten Pahle
  • StevertIgo
  • Dieter: Rather than a WME, I completely revised this page. There were both incorrect statements and too technical comments on it for a basic explanation. I avoided technical issues by including "generally speaking". Check out the [ext] previous version and recover what was left out unjustified.


Path: LifeAndDeath   · Prev: Eyes   · Next: EyeSpace
Path: EyesCollection   · Prev: Eye   · Next: FalseEye

This is a copy of the living page "Two Eyes" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.