Pair ko rule: a practical alternative to superko

[luigi]

I have come up with a new way to prevent cycles. I call it the pair ko rule. It goes like this:

There is an off-board location called memo. Whenever you make a play immediately after an enemy play in your territory, add to the memo an entry with your opponent's last move, your current move and your color. Do not include information about captured stones. Some examples of valid entries are "B6 M15 Black" and "O10 D4 White". Your territory is all empty regions touching your stones only.

You cannot make a play that requires you to repeat an existing entry on the memo. Passing is always allowed. Suicide is not allowed.

For convenience, this rule can be complemented with the basic ko rule. Otherwise, every ko can be taken three times in succession before the first ko threat is needed. This makes the game longer but does not change the result.

Since highly skilled players can replay their games from memory, I think they would have no trouble complying with the pair ko rule even without the memo. Note that this only requires players to keep track of 17 new bits of information for every play in enemy territory, while superko requires keeping track of 573 new bits for every move.

Pair ko produces almost the same game as superko, but it affects long cycles differently. It also turns double-ko seki into a complex ko fight, which seems good news to me. Does it change the result of any other non-cyclical positions? Do you think it would be a good replacement for superko?

(As an aside, since all forced cycles include at least one sequence of two consecutive plays in enemy territory, the rule could even be simplified to: "Do not repeat a sequence of two consecutive plays in enemy territory, one by each player. A play is defined by its color and its coordinates, regardless of any captures it makes." This would still allow cooperative cycles, but those are not a concern.)

[Schachus]

I do not understand how you imagine this to work. After the first capture in a ko, can i recapture immediately without playing a ko threat? It seeems so, I dont see what would prevent it.
Also: is move 2 by white a move in blacks „territory“?

[luigi]

After the first capture in a ko, can i recapture immediately without playing a ko threat? It seeems so, I dont see what would prevent it.

Yes, if the basic ko rule is not used, you can recapture immediately, but so can your opponent. After your opponent recaptures, you cannot recapture again, so you end up in the same situation as if you hadn't recaptured. That's why I said this produces the same result as the basic ko rule, even though it takes longer to get there.

Also: is move 2 by white a move in blacks „territory“?

Yes.

[luigi]

The rule can be stated more concisely like this:

You cannot play at point B immediately after an incursion by your opponent at point A if, on any earlier turn, you played at point B immediately after an incursion by your opponent at point A. Passing is always allowed. Suicide is not allowed.

An incursion is a play by one player in a territory owned by the other player. A territory is a maximal set of connected empty points. You own a territory if all stones connected to it are of your color.

[Schachus]

I like that formulation better than the list.
It is very counterintuitive that an „under the stones ko threat“ can‘t be used in the same ko as the threat before, but can be used in a different ko. I do think this could actually affect „normal“ play, where we have no double kos or antything like it

[luigi]

I like that formulation better than the list.
It is very counterintuitive that an „under the stones ko threat“ can‘t be used in the same ko as the threat before, but can be used in a different ko. I do think this could actually affect „normal“ play, where we have no double kos or antything like it

I actually see the lack of double ko as a good thing. It means you cannot have an unlimited number of unremovable ko threats, and moonshine life can be killed.

[Elom0]

In the past few weeks I thought of the idea to replace the ability to pass with the ability to repeat any sequence of moves that have been played. If both players do this then the score is counted. That way you don't have to remember whole board positions but just which mo es have been played