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| No Repetition (A rule called “Ko”)

No repetition ever.

Full disclosure - this is a rule that may confuse you at first. Fortunately, it is not as complicated as it appears at first glance. I for one think that a good ko fight is one of the most fun things you can have in Go, although many would disagree.

A game of Go can be really long. However, it must never be endless. To prevent the possibility of an endless game we have a rule called “Ko”.

Just imagine a situation like this one. Given enough stubbornness, players like these would be playing until they pass out. Feel free to watch for a while.

ko diagram

To prevent health problems connected with exhaustion, we have the following rule:

A completely identical board position must not appear twice in one game.
Therefore, before you can recapture a stone that just captured yours, you have to play elsewhere at least once.

Can you ever capture that stone then? What are your options? Basically, you have two:

⬤ You deem the stone not important for now and play elsewhere, letting your opponent end the ko by connecting her endangered stone if she wants.

⬤ You deem the stone important enough to fight the ko. You still have to play elsewhere, but you try to find a move your opponent will feel compelled to answer to immediately instead of resolving the original ko; we call this a ko-threat. After that, you retake the ko stone and the fight is on!

Confusing? Check out the following examples. It will be clear in no time.

Black to play

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On the 19x19 board, there are usually much more than only one threat, so the ko fight can span several moves. The hard part, of course, is judging if a given threat is big enough that it needs to be responded to or whether it is more beneficial to end the ko. But hey, I said the rules are easy, not the game itself.

Let me get back to this one later
I understand,
what's next?