Is this a bot bug, an AI bug or a feature?

In this game, AI suggests A2 for move 42, but during the game it didn’t let me play there, stating it was ko.

Its private game :<

I’m sorry, it must have been by mistake, I don’t make my games private. I can’t find you as _KoBa, please tell me how to add you.

EDIT: I gave the OGS group access, hopefully almost everyone is there :-). Everyone else who wants access, please ask, sorry for the inconvenience.

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Works now. Game is played under chinese rules, a2 is banned because superko rules, its case of “sending two, returning one”

I’m bit surprised why kata recommends playing it, i thought it it knows superko rules xD


When I tried playing it and it said fobidden move because ko, I remembered I had asked a similar question a while ago, but then AI suggested that move and I was confused. :frowning:


Yes, KataGo does support positional superko. So OGS might have the wrong rules configured. For OGS, the correct rules to use in KataGo should be “chinese_ogs” which tries to match Chinese rules “as implemented on OGS”, i.e. Chinese rules with positional superko. Probably OGS is telling KataGo to use Chinese rules with simple ko right now.

One point of confusion might be the common belief (misconception?) that the Chinese rules everywhere use positional superko (i.e. not just Chinese rules on OGS/KGS). This probably arises from the fact that their written rules say they use positional superko. But, just as with Japanese rules, the situation in real life is more subtle.

I think what’s going on is that none of the professional Go associations in China/Japan/Korea care much about the written rules. They care some, but not much. The obsession with writing down exact rules is more of a Western thing. For the Asian Go associations, the rules are defined by the collective traditions and precedents that association and the intuitions of the professional players who play the game. Writing them down is secondary, and when the written rules disagree with practice, the written rules are ignored.

So in this case, it turns out that Chinese players generally use a simple ko rule, despite the written rules. You can see this because triple ko comes up every few years in league games or other matches or events, and it’s ruled as voiding the game (“no result”). Nobody tries to fight out the triple ko for real under superko.

You can find another provision that allows tournaments and competitions to use “alternate” rules - so you could say that technically the Chinese rules do use positional superko, it’s just that every tournament and every league universally overrides to “alternate” rules of simple ko. But that’s kind of the point - the written rules aren’t the real rules that everyone uses.

How to deal with sending-two-returning-one then? You simply say “sending two returning one” is illegal. So the real rule is “simple ko, except also sending two returning one is illegal”. Actually there’s also moonshine life too. So you also say “moonshine life is illegal”.

KataGo for now doesn’t support “simple ko, except also sending two returning one and moonshine life are illegal”. I could try to implement “simple ko, except also sending two returning one is illegal”, and maybe I could find some heuristic to also ban moonshine life too while still leaving “true” triple ko as a no result. But at least here, it’s not relevant - “OGS Chinese rules” uses positional superko, even practical Chinese professional rules don’t, so I think OGS just needs to tell KataGo to also use positional superko. (Or to demonstrate an actual test case with a bug in KataGo itself, and then I’ll fix it. :slight_smile: )


Where were you @hexahedron when I needed you? :heart:

(kidding plz don’t revive that thread)