From the official rules:
These are essentially the New Zealand rules, re-worded to be as simple and elegant as possible. The NZ rules are in turn the simplest version of Chinese-style rules around. The NZ rules are worded with definitions given recursively, which is elegant and a joy to computer scientists, logicians and mathematicians, but perhaps not so nice for most others. John Tromp came up with the key idea of a stone “seeing” (or as I’ve presently worded “reaching”) a different color. This was the brilliant step which enabled such succinct rules. My modest contribution was the wording for the end-of-game criterion, and putting an expansion into a second tier of interpretations rather than rules. This was
- to keep the logical rules as simple as possible, and
- to keep things close to how the game is actually played by humans.
And a fun fact about OGS’s implementation of New Zealand rules: