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``.
|Table of contents||Table of diagrams
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.)