Editing Rules of Go (section)

=== Repetition ===
The major division in rules to prevent repetition is between the simple ko rule and the super ko rule: the simple ko rule (typically part of the Japanese ruleset) prevents repetition of the ''last'' previous board position, while the superko rule (typically part of Chinese derived rulesets, including those of the [[American Go Association|AGA]] and the [[New Zealand Go Society]]) prevents repetition of ''any'' previous position. In both cases, the rule does not, however, prohibit passing.

The super ko rule is differentiated into situational super ko (SSK, in which the "position" that cannot be recreated includes knowledge of whose turn it is) and positional super ko (PSK, which ignores whose turn it is). Natural situational super ko (NSSK) is a variant in which what matters is not whose turn it is, but who created the position (i. e., who made the last move other than a pass.)

The Ing rules feature a complicated distinction between "fighting" and "disturbing" ko.

Situations other than ko which could lead to an endlessly repeating position are rare enough that many frequent players never encounter them; their treatment depends on what ruleset is being used. The simple ko rule generally requires the inclusion of additional rules to handle other undesirable repetitions (e.g. long cycles which can lead to ''no result'' where the game must be replayed).

The first position below is an example of a ''triple ko'', taken, with minor changes, from Ikeda Toshio's ''On the Rules of Go''.<ref>[http://gobase.org/studying/rules/ikeda/?sec=e2030601 European Go Culture Centre Homepage]</ref>

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Goban 9x9

| | | | | | | | | 
|b|b|b|b|b|b|b| | 
|w|w|w|w|w|w|b| | 
| |w| |w|b|w|b|b| 
|w|b|w|b| |b|w|b| 
|b|b|b|b|b|b|w|b|b
| |w|w|w|w|w|w|w|w
|w|w| |w| | | |w| 
| | | |w| | | |w|

|24|u=u|d=d|l=l|r=r}}
|&nbsp;&nbsp;
|
{{Goban 9x9

| | | | | | | | | 
|b|b|b|b|b|b|b| | 
|w|w|w|w|w|w|b| | 
| |w| |w|b|w|b|b| 
|w|b|w|b| |b|w|b| 
|b|b|b|b|b|b|w|b|b
| |w|w|w|w|w|w|w|w
|w|w|b|w|b|b|b|w| 
|b|b| |w|b| |b|w|b

|24|u=u|d=d|l=l|r=r}}
|&nbsp;&nbsp;
|
{{Goban 9x9

| | | | | | | | | 
|b|b|b|b|b|b|b| | 
|w|w|w|w|w|w|b| | 
| |w| |w|b|w|b|b| 
|w|b|w|b| |b|w|b| 
|b|b|b|b|b|b|w|b|b
| |w|w|w|w|w|w|w|w
|w|w| |w| |w| |w| 
| |w|w|w|w|w|w|w|w

|24|u=u|d=d|l=l|r=r}}
|-valign="top"
|Triple ko; Black kills group (PSK, SSK)
|&nbsp;&nbsp;
|Result if White moves first (NSSK) 
|&nbsp;&nbsp;
|White wins here with first move. (NSSK)
|}

Without a superko rule, this position would lead to an endless cycle, and hence "no result", a draw, or some other outcome determined by the rules.

For simplicity, when discussing this position using the superko rule, it is assumed that the last move placed a stone in a position unoccupied since the beginning of the game, and away from the ko. Under positional and situational super ko, Black captures the white group. This is also the case with natural situational super ko if it is Black's turn. If it is White's turn however, then NSSK exhibits odd behavior. White can get a seki by passing, but only at the cost of allowing Black unlimited moves away from the ko. If White insists on saving their group, the final position might look like the second diagram. On the other hand, with the first move (which should be a pass), White wins by two points in the third position using NSSK (assuming area scoring). Black's best response, in terms of maximizing their score, is a pass.