Chinese Rule Sharpness
This page aims to provide a simple position in which Chinese Rules are “sharper” than Japanese Rules, where (as indicated in the article Sunjang Baduk Counting) a rule set ``R`` is considered “sharper” than another rule set ``S`` in a certain position if fewer moves are optimal in that position under ``R`` than under ``S``.
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Black to play
takes ko, fills ko
Theoretically, gains ⅙ pt. less than , but it is correct in this case to play it first, to force White to win the ko. After the ko exchange, gains 1˝ pt., gains 1⅓ pt., and then gains 1 pt, for a net gain to Black of 1⅙ pt. Black wins by 1 pt.
takes ko, fills ko
Locally gains 1˝ pt. and gains 1 pt., so locally Black has a net gain of ˝ pt. But globally Black has a net loss of ⅚ pt. How come? The reason is that, because White was komaster, with the drops in temperature, the ko lost a total of 1⅓ pts. At first it was worth ⅔ pt. for White, at the end it was worth 2 pts. for White. This is a good example of why the koloser should start the ko fight.
RobertJasiek: What does "sharpness" in the page titles mean?
Bill: Maybe the original author will let us know.
[ ]: it is from Sunjang Baduk Counting. See paragraph containing link to this page.
[ ]: Considering what sharpness means here, one can create a counting system that says "its a draw". This would be "not sharp" or have a sharpness of 0 as all moves lead to a draw. The claim that one out of area and territory counting is sharper may be based on the idea that there are more board arrangements where playing differently causes a change in the result when using one system than there are when using the other one.
Bill: OK. So a small Black mistake on this board costs 2 pts. in the end, while a small Black mistake on the Japanese Rule Sharpness board costs only 1 pt. But that why the difficult to understand ko positions?
[ ]: The smallest change when using area counting is two points. (OK, one point if we're looking at some lengthy sequence where one line leads to a draw involving a seki with an odd number of dame, and the other a one point win (see One Point Area Scoring Swing)). Regarding the ko positions, they were the easiest I could create. It is not simply a matter of the mistake costing x points, it is also then when the other counting system is used, the mistake costs 0 points. The Japanese Rule Sharpness page is an example of "...by Japanese counting Black may have only one option that wins by 1 point, while another results in jigo". The Chinese Rule Sharpness page is an attempt to create the same situation by Chinese counting, although it doesn't quite succeed because of the minimum 2 points swing and the difficulties in arranging a jigo.
Bill: On an odd parity board, with no komi, it is not at all difficult to construct a position where Black to play loses 1 pt. by a mistake to get jigo under Japanese scoring, while the same "mistake" costs nothing and is a 1 pt. win under Chinese scoring, because Black gets the last dame. That is an example of the condition in your final sentence.
[ ]: the Japanese Rule Sharpness page provides such a position. If you have a simpler example then to provide it would improve the page.
Bill: Well this page has an example of how the mistake under Chinese scoring, which loses 2 pts., loses nothing under Japanese scoring, because the ko loses only ⅓ pt. by the temperature drop instead of 1⅓ pt. (Black does not play , OC.)
Impact of ButtonGo on outcome
nola: Am I correctly evaluating this using Button Go rules? It seems like those rules can distinguish both this case and the Japanese Rule Sharpness example, and that after accounting for the impact of Komi adjustments, you get the "right" outcome in both cases: precise play is rewarded. Is this true in general? Or is it an artifact of these two examples?