Superko in KGS Computer Go Tournaments

In over a thousand games played in computer Go tournaments on KGS, six games have been ended by the Superko rule. In four of these four cases, the effect of the rule effectively decided the result of the game.

Forms of Superko rule.

There are three forms of superko rule:

PSK	Positional SuperKo	A player may not play a stone so as to recreate a previous board position from the game.	This refers to the position just after the play and consequent removals.
SSK	Situational SuperKo	A player may not play a stone so as to recreate a previous board position from the game, with the same player to move next.	Recreation refers to the position just after the play and consequent removals, and also takes account of who moves next.
NSK	Natural Situational SuperKo	A player may not play a stone so as to recreate a previous board position from the game, if s/he played to create it previously.	This refers to the position just after the play and consequent removals.

All forms of superko rule refer only to playing of stones. It is always legal to pass, whatever form of the rule may apply.

Chinese Rules of Go

Computer Go tournaments on KGS have so far always used "Chinese Rules", as implemented on KGS.

The intention of the Chinese Rules of Go about repeated positions is unclear. Section 6, as translated into English in "The Go Player's Almanac", Richard Bozulich, 1992, reads in full:

Reappearance of the same board position is forbidden throughout the game.

However, section 20.3 reads:

3. In rare situations such as triple ko, quadruple ko, eternal life, and round-robin ko, if neither side will yield, the referee may declare a draw or replay.

These two sections appear to be in contradiction. The implementers of KGS have resolved this by giving priority to the section which appears first, and implemented Positional Superko.

Superko incidents in KGS Computer Go tournaments

The application of the Positional Superko rule has six times affected a computer Go tournament game on KGS. These incidents have all be mentioned on the reports of the event, and are listed below.

date (link to report)	What happened
September 2005	Viking5 was unable to play the move it wanted against gonzoBot, and so resigned, in what would otherwise have been a won position.
October 2005	Dariush timed out in a won position against SlugGo, when prevented from playing the move it wanted.
November 2007	Break timed out in a lost position against FirstGoBot, when prevented from playing the move it wanted.
December 2007	MonteGNU timed out in a won position against WeakBot50k, when prevented from playing the move it wanted.
September 2008	SimpleBot timed out in a won position against WeakBot50k, when prevented from playing the move it wanted.
October 2008	HouseBot timed out in a lost position against ManyFaces, when prevented from playing the move it wanted.

All of these positions involved the Sending two, returning one shape. None of the moves involved would have been forbidden by Situational Superko or by Natural Situational Superko.