Chinese Ko

    Keywords: Theory

Elwyn Berlekamp and Yonghoan Kim use the expression Chinese Ko in their paper Where Is the “Thousand-Dollar Ko”?,[1] apparently to refer to a ko that can only be worth fighting when Chinese (area) scoring is in force.

The ko in question looks similar to this, where all stones except the marked stones are independently alive:

[Diagram]
Chinese ko  

With Japanese (territory) scoring, there are no points to be gained here: we expect Black to connect at k and White to connect at w or b. With area scoring, however, it turns out that it can be worth fighting this ko!


[Diagram]
Normal sente  

With area scoring, if Black is not komonstrous, then ​ W1 B2 ​ is sente, after which circle is a normal dame. ​ ​ ​ (With Japanese scoring, W1 is a tiny ko threat and B2 is the reply.)


[Diagram]
Black's alternative  

With area scoring, if

Black has "sufficiently many kothreats that" Black "can avoid filling" k "until after all dame are filled and White is forced to either pass or fill in a point of" White's "own territory while" k "remains empty and surrounded by Black", then

B1 W2 ​ is sente, after which Black gets k as if it was a one-sided dame for Black.

(The quotes are from page 216 of [1].)



References

[1] Where Is the “Thousand-Dollar Ko”?, Elwyn Berlekamp and Yonghoan Kim, Games of No Chance, MSRI Publications?, Volume 29, 1996, [ext] http://library.msri.org/books/Book29/files/kim.pdf .

This paper analyses four problems based on a minor variants of a position that appeared on the inside cover of Go World, issue 70. In each case, one assumes that the winner collects a prize of $1,000. If he wins by more than one point, he can keep the entire amount, but if he wins by only one point, he is required to pay the loser $1 per move. The problems require one to say how long the will game last in each case.

Chinese Ko last edited by RickyDemer on May 16, 2019 - 01:23
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