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The Magic of Ko
January 13, 2003
By Roy Laird

The "ko" rule, which ensures a result in nearly every game by avoiding endlessly repetitive situations on the board, leads to situations of fascinating complexity: double and triple kos, multi-stage and multi-step kos, "hot" and "cold" kos, flower-viewing kos, thousand-year kos, "super-ko" and thousands of other peculiar positions, including the mind-bending "molasses ko." In truth, few if any of us truly understand the depth of those complications. Ko fights often decide games, especially if one player is afraid. Life and death problems often center on the question of finding, or avoiding, ko. 

Ko is the only rule to be the subject of an entire book (Fighting Ko by Jin Jiang, available from Yutopian Enterprises.) Nonetheless, we were surprised to discover dozens of web pages devoted exclusively to this topic. We were looking at Rob Van Ziejst's wonderful column, "The Magic of Go," which appears in the online English language Yomiuri newspaper. A discussion of pon-nuki, the four-leaf-clover shape that captures a stone, gradually evolved into a discussion of ko, which is created when two ponnukis of opposing colors overlap. Column #192 at http://www.yomiuri.co.jp/igo_e/ is a good place to jump in. Better yet, go back and read all 192 in order. They're great, especially for new players.

Sensei's Library, a set of user-maintained pages, contains two separate collections of pages on the subject. Learn the basics at http://senseis.xmp.net/?KoFighting, then move on to "The Second Course of Ko" at http://senseis.xmp.net/?SecondCourseOnKo. where you can learn about such arcane subjects as "Moonshine Life," the earliest known rules dispute, which arose during a game played in Japan in the 13th century.

We thought we had completely exhausted the subject, until we discovered a series of ten lengthy essays by Britis author Charles Matthews at http://gobase.org/studying/articles/matthews/ko/. Here you can learn even more about how to calculate the value of a ko fight, how and when to start a fight, how to understand "bulge ko" and "apex ko", how to block with implied ko, how to take a ko's "temperature," and other subjects. 

Sensei's Library (above) also contains a number of "party-trick" positions, more perplexing than plausible setups such as "Molasses Ko" and "Pinwheel Ko". If these entertainment's strike your fancy, you won't want to miss Harry Fearnley's "Bestiary" at http://www.goban.demon.co.uk/go/bestiary/zippersetc.html. You may never see a "zipper", a "loop" or a "train" in a real game, but they're fun in their own way. You'll also want to check out Matthew Macfadyen's collection at http://www.goban.demon.co.uk/go/bestiary/molasses_ko.html Animated versions of some of these positions can be viewed at http://www.britgo.org/rules/molasses.html and http://wwwhomes.uni-bielefeld.de/achim/goloopy.html

For a different perspective, check out Robert Jasiek's extensive discussion of the subject at http://home.snafu.de/jasiek/korules.html. Jasiek is particularly interested in classifying and comparing various rule sets according to their handling of ko, a subject he discusses thoroughly at http://home.snafu.de/jasiek/koclass.html. It seems that ko, like go itself, is so vast as to defy complete description.

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