[Welcome to Sensei's Library!]

StartingPoints
ReferenceSection
About


Aliases (info)
Eyes

Paths
Shape
LifeAndDeath
EyesCollection

Referenced by
Miai
EyeSpace
CapturingRace
TwoEyes
FalseEye
Extension
ThrowIn
BigEye
TheSecondBookOfGo
UnderTheStones
GeneralEyeDefinition
TwoLiberties
EyeLiberties
EyeDefinitionDisc...
ShutIn
NoEyeVersusNoEyeC...
EyeStealingTesuji
AtariGoAsATeachin...
DiagonalPlayRefer...
SekiWithEyesQuestion

 

Eye
Path: EyesCollection   · Prev:   · Next: TwoEyes
  Difficulty: Introductory   Keywords: Life & Death, Go term

Eyes are a central concept in Go, since two eyes guarantee the life of a group. And one eye can mean a great advantage in a semeai (capturing race). Beware of a false eye that may look like an eye.

In general, what Go players call an eye is an empty space surrounded by stones of one colour.

[Diagram]
An eye in the centre

[Diagram]
An eye on the side

[Diagram]
An eye in the corner


There is much discussion on the definition of what is an eye and what is not. The recognizing an eye page describes a non-mathematical way of recognizing an eye. There are also discussions of technical algorithmic definitions meant mainly for mathematicians and computer programmers, where absolute precision is needed.


Grauniad: Why do all the examples of eyes on this and related pages contain a single point? Can't an eye contain more than one point? Won't single-point examples of eyes mislead readers?

Stefan: An eye can indeed contain more than one point, as no doubt you know. Everybody figures that out in due time though, and I do believe there is more room for confusion of beginners if we include examples with more than one point.

Dieter: We could do it, dividing this page into several sections.

Velobici: Providing diagrams of a single eye with two spaces right next to the diagrams of a single eye with one space should not be confusing. It will clarify the matter for the beginner that two space is not two eyes unless the spaces are disconnected from each other.

Bill: Another thing is that there are things that are true about single point eyes that are not necessarily true about larger eyes. Larger eyes can be more complicated. For understanding, best start with single point eyes. :-)


TJ: Something I point out to beginners, which seems often taken for granted as known, about forming eyes. If a group has more territory, it is more likely to be able to live if invaded. Whether it can live or not depends on shape. If the shape is seven points of territory or more, it cannot have its eye space compromised with correct defense, and can make two eyes.

Bill: Sorry, TJ. That's not true. What is true is that a solidly connected group with an eye of at least 9 points can live. (With only 8 points in the corner, ko is possible.) But that life might be seki.
TJ: Don't be sorry...show me!:)[1] The eye space page lists only one seven point shape which can be made seki (butterfly seven) as of this writing, and no eight point shapes, which even then is more than I've learned from other sources.
Velobici: There is one group with all its stones solidly connected one to another that lives or dies according to who plays first. It is the Carpenter's Square. Please note that the group is not connected to the edge of the board on either side. So it most likely does not fit Bill's concept of solidly connected.
TJ: Carpenter's Square isn't a group with a single completed eye of undetermined status yet, though. The groups I was mentioning, of shapes from 3-6 points, is meant to refer to such sealed-in, completed eye shapes, and how to determine status...do you have to play to live? Can you defend if attacked? Where is the vital point? Next step is looking at: Where is the vital point GOING to be when the group is totally sealed on all sides, and can I play there? Can I avoid making bulky-five in gote? Is it going to be square four if I play (move)? I mean to be talking about the basic shapes which groups which become cut-off get ultimately reduced to. What is the appropriate term to refer to this sort of basic shape concept? Eye space is maybe ambiguous, is that the source of confusion? Eye shape a better term? Help!:)

Less than seven points, it depends on shape of the territory surrounded. So, a good starting point for beginners is to learn the status of the territory shapes between three and six. That's not such a huge task, and makes all that life and death stuff you keep hearing is so important a lot more comprehensible; not to mention stopping you from considering attacks that just won't work and freeing you to look elsewhere, and helping you stop wasting time with over cautious defense of perfectly safe groups in your games. On SL, check out Eye Space to learn all about these important shapes.

Further ramifications directly deduced from this once the shapes between 3 and 6 are understood: Problems of Life and Death, both as exercise and within games, boils succinctly down to: Can a group can be cut off, and the territory it holds reduced to less than seven points of a shape which can be killed (death)/can such an occurance be avoided, or made to depend on the outcome of a Ko which will give the group life if won or give the player compensation for the killed group if lost (life).

Capturing races are just a form of the same thing in which two opposing groups are trying to live/kill each other at the same time.

Is this a good concise way of talking about what eyes are all about, and how to learn about them? If this is off topic, or is better stated elsewhere, or just too long winded, forgive me...I'm new here.:)


TJ: Given the discussions can I re-edit this to read something like:

...if the shape is seven points of territory or more, it can be defended to a minimum of life in seki or can form a ko. For large-eye shapes which can be reduced to seki or ko, find examples at Nine Point Eye - Possible Seki, Eight Point Eye - Possible Ko, Butterfly Seven.

And then carry on with the rest pretty much as is?


[1] See Nine point Eye - Possible Seki and Eight point Eye - Possible Ko



Path: EyesCollection   · Prev:   · Next: TwoEyes
This is a copy of the living page "Eye" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.