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Unconditional Life
  Difficulty: Beginner   Keywords: Life & Death, Go term

Jan: I found I needed the following definition to understand Benson's Algorithm.

A group of stones is said to be unconditionally alive if it can never be captured, even with the opponent playing against the group as many times as he wants.

Examples:

[Diagram]
Diag.: An unconditionally alive group

No matter what White tries against this group, it can not be captured.


[Diagram]
Diag.: This group is not unconditionally alive

This group, although it is normally considered alive, can be captured by White - by playing at a, b, c and d for example.



jvt: Benson's terminology is confusing: unconditionally alive usually means alive without ko in Go literature.

Charles Matthews The point here would be that 'alive', the status of a group, isn't the same as 'no possible threats' against it', as in 'no ko threats ever possible'. Absolutely alive expresses the idea better, perhaps.

Dieter: Almost all analyses of Go positions are based on the assumption of (local) alternating play. The case where one of the players tenuki, is (should be) stated explicitly and should not determine the classification of the position. Therefore, unconditional life assuming alternating play is a much more useful concept than unconditional life assuming a free road for either side and the latter should IMHO not be the meaning of unconditional life. A ko implies that the assumption of alternating play is disturbed in a very explicit way, so the ko becomes the condition on which life hinges.

Bill: My own sense, since long before hearing about Benson's terminology, has been that being able to live with alternating play, even when the opponent plays first, simply means being alive, not unconditional life. Unconditional life means being alive, no matter what the opponent may do.



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