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Two-Step Ko
Path: SecondCourseOnKo   · Prev: ApproachKo   · Next: TwoStepOneMoveApproachKo
  Difficulty: Beginner   Keywords: Ko

Two-step ko

In a two-step ko taking the ko produces another ko mouth, which must be taken before winning the ko. Example:

[Diagram]
Diag.: Two-step ko


Note: a two-step ko is not the same as an approach ko.

See Two Step One Move Approach Ko.


Yes, a two-step ko is the same as a one move approach ko. What you have there is called a two-stage ko.

To see whether it was me or you that was mistaken, I did a google search on 'two step ko'. Here are the results:

In favor of two step ko=one move approach ko:

In favor of two step ko=two stage ko/nidanko:

Unclear:

I had expected the term to come up more often; nevertheless, it's 4-0 in favor of my definition, and with at least one of them (Rob van Zeijst) being a person who should be 'in the know'. -- Andre Engels


First, with all respect, Andre, I have to admit that I would have found it more polite if you had discussed this before changing the page. As for the discussion itself: I would definitely favor to use "two step ko" in the sense of "two stage ko", as I find it more logical (apart from better corresponding to the japanese wording).

As for the current use in English: I don't think it is as clear as you think. The diagram in [ext] http://www.yutopian.com/go/gowinds/gw32.pdf that you couldn't see actually shows a nidanko[1]. As for books: In "Attack and Defense", "two step ko" is used in the sense of one-move approach ko. Whereas, according to [ext] http://math.stanford.edu/~carlton/go/y4.html, the book "Fighting Ko" by Jin Jiang uses "two step ko" in the sense of nidanko.

So if one doesn't want to be misunderstood, one should probably avoid the term "two step ko". But as the current usage is unclear, I think it would be fair to try to build a consensus about what it should mean, and then recommend this usage. SL is becoming a reference for Go Terms, so this is a valid thing to do. --dnerra

Charles Matthews The source of this terminology is Life and Death by James Davies (1975). That is why the Ishi Press books put it that way. I have in fact corresponded with Jim Davies about this point, and it seems he now regrets this choice of translation. So I simply avoid using these terms. But to say that once a translation is made by somebody, that defines usage for ever, is too conservative for me. There is still plenty of poor and misunderstood terminology in the English literature.

Bill Spight: One point everyone seems to agree about is what an n-step approach ko is. That being the case, I think that we should restrict ourselves to that and *not* call approach kos step kos.

Given the confusion, I agree that it is better to avoid simply referring to step kos. Despite a bit of awkwardness, I like Simon Goss's suggestion to refer to dan kos as iterated kos. Then we would call the ko above a two-step iterated ko.

[1]

[Diagram]
Diag.: GoWinds "Two-step ko"


Path: SecondCourseOnKo   · Prev: ApproachKo   · Next: TwoStepOneMoveApproachKo
This is a copy of the living page "Two-Step Ko" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.