Sending three, returning one

Sending three, returning one  

This looks like a seki, but Black can make a throw-in ko.

Sending three  

First, Black sacrifices three stones.

Returning one  

Then he captures White's stone.

Ko  

= pass.

After White's pass throws in for a two-stage ko.

Note that White cannot prevent the ko with at , as that makes a dead shape.

Repetition  

, = pass.

repeats the original position. If the rules allow it, can continue the cycle.

This cycle causes potential problems for the rules. For instance, rules with area scoring but no superko rule. Ing rules fall into this category. They probably classify this as a disturbing ko. Rules with territory scoring that end play with consecutive passes could continue indefinitely if the players collude. Otherwise, White can eventually give up his stones and still win. Rules where a pass lifts ko or superko bans also face a problem. Ing rules and Spight rules fall into this category. Spight rules prevent indefinite repetition by stopping play when the same player passes a second time in the same position. In this cycle, that would occur with .

More on the /Discussion page.