Jay Burmeister Janet Wiles Departments of Computer Science and Psychology The University of Queensland, QLD 4072, Australia Technical Report 339, Department of Computer Science, The University of Queensland, 1995 (This document is - permanently - under construction). See also: Jay Burmeister’s PhD Thesis (2000) Table of Contents 1.0 Introduction 2.0 The Game of Go 2.1 Liberties and Capture 2.1.1 Suicide 2.2 Strings 2.3 Eyes 2.3.1 Dead or Alive 2.3.2 False Eyes 2.3.3 Seki 2.4 Repetition of Board Positions - Ko 2.5 Sente and Gote 2.6 Ladders 2.6.1 Snapbacks 2.7 Links 2.8 Groups 2.9 Armies 2.10 Winning the Game 2.11 The Go Handicap and Ranking System 3.0 The Challenge of Programming Go 3.1 A Comparison of Chess and Go 3.2 The Complexity of Go 3.3 Why Go Cannot be Programmed Like Chess 4.0 History of the Computer Go Field 4.1 Academic Work 4.1.1 Zobrist 4.1.2 Ryder 4.1.3 Reitman and Wilcox 4.1.4 Other Academic Work 4.2 Programs 4.2.1 The Many Faces of Go 4.2.1.1 G2 4.2.1.2 Cosmos 4.2.1.3 Many Faces of Go 4.2.2 Go4++ 4.2.2.1 Candidate Move Generation 4.2.2.2 Evaluation Function 4.2.2.3 Performance and Timeline 4.2.3 Handtalk 4.3 Computer Go Competitions 4.3.1 The Ing Prize 5.0 What's in a Go Program? 6.0 Performance of Current Programs 6.1 Program versus Program Performance 6.2 Program versus Human Performance 7.0 Future Improvements in Performance 8.0 Go and Computer Go Resources on the Internet 8.1 Computer Go related Internet Resources 8.1.1 Anonymous FTP Archive and Mirror Sites 8.1.2 The Internet Go Server (IGS) 8.1.3 Game Record Formats 8.1.4 The Computer-Go Mailing List 8.1.5 The Computer Go Ladder 8.1.6 Computer Go Competitions/Tournaments and Results 8.1.7 Computer Go Bibliographies 8.1.8 Game Databases 8.2 Go Related Internet Resources 8.2.1 Go Rules and Learning to Play 8.2.2 Go Learning Aids and Tutorials 8.2.3 The Go News Group 8.2.4 The Go Frequently Asked Questions (FAQ) 9.0 Conclusions Appendix A Common Go Terms and Their English Equivalents References 1.0 Introduction This document introduces the reader to the computer Go field and Internet resources pertaining to Go and Computer Go. For readers unfamiliar with Go, section 2 describes the rules and common concepts of the game. Readers comfortable with their knowledge of Go may skip section 2, reading it only if the use of terms in this document needs clarification. Section 6 describes the current state-of-the-art in Go programs which is far behind that of Chess programs even allowing for the comparative disparity in the amount of effort expended on developing programs for each game. Theoretical and practical reasons are given in section 3 for this disparity as well as reasons why Go cannot be programmed in a similar fashion to Chess (see Table 1 for a brief comparison). The history of the computer Go field is briefly outlined in section 4. Included in this outline are descriptions of some of the academic work that has used Go as a vehicle to pursue research, computer Go competitions and results, and programs. Internet resources pertaining to Go and computer Go are described in section 8. The resources listed include a server for playing a game of Go, an FTP archive site and a mailing list which provides a forum for discussing aspects of programming Go. 2.0 The Game of Go Go is a two player board game in which chance plays no part. It is an Oriental game which originated between 2500 and 4000 years ago and enjoys a similar status in Japan, China, Taiwan and Korea as Chess does in Western countries. Go is played on a board which consists of a grid made by the intersection of horizontal and vertical lines. The size of the board is generally 19 x 19, however, 9 x 9 and 13 x 13 sized boards are also used for playing quicker games. Intersection points are connected along the horizontal and vertical lines such that the neighbours of any given point are the intersection points that are horizontally and vertically adjacent to it. Two players alternate in placing black and white stones on the intersection points of the board (including edges and corners of the board) with the black player moving first. The aim of Go is to capture more territory and prisoners than your opponent. 2.1 Liberties and Capture Empty points that neighbour a stone are called its liberties (points marked L in Figure 1). Any stone which has no liberties is captured and removed from the board (white stone in Figure 2). This is the only instance in which stones, once placed, are moved. 2.1.1 Suicide A player cannot commit suicide by placing a stone in a position which leads to its immediate capture (points marked X in Figure 3). 2.2 Strings Stones of the same colour can be joined into strings by being horizontally or vertically connected to each other (Figure 4). Single stones can also be described as strings which we will refer to as unitary strings. Instead of the stones in a string having individual liberties, the liberties of the constituent stones of the string become the liberties of the string (points marked L in Figure 5). To be captured, a string must be surrounded by opponent stones such that no stone in the string has any liberties (black stones in Figure 6). When a player fills the penultimate liberty of a stone or string, it is courtesy to declare "Atari!" which alerts the owner of the stone or string of its impending capture. 2.3 Eyes Eyes are formed when a string surrounds one or more empty intersection points (point marked E in Figure 7). Strings which contain a single eye can be captured by first being surrounded and then the eye being filled (Figure 8). Filling the eye does not violate the suicide rule since the opponents captured stones are first removed, creating liberties for the last stone played. A string that has two eyes (points marked E in Figure 9) is safe from capture since there is no way for an opponent to capture such a string. The reason for the inability to capture a string with two eyes is that the stone played in the first eye will be subject to the suicide rule. Dead or Alive Strings which have two eyes are said to be alive. In general, a string is alive if it cannot be captured even if the opponent moves first. A string is considered to be dead if there is no way to stop it from being captured even if its owner moves first. 2.3.2 False Eyes 2.3.3 Seki 2.4 Repetition of Board Positions - Ko To stop endless cycles occurring, a player cannot play a stone which causes a previous board position to be repeated. In general, the only situation in which a cycle can arise is called a ko. In Figure 10, a white stone at 1 is captured by a black stone at 2 which could itself be captured by a white stone being played at 1 again. Such a situation is prohibited by the rule against repetition. A ko situation can lead to a ko fight (Figure 11) in which the player which loses a stone in the ko (white stone at 4 captured by black at 1) threatens an opponent stone elsewhere (at 2) and then recaptures the opponent stone in the ko (at 4) after the opponent responds to the threat (at 3). 2.5 Sente and Gote Skilful players can engineer the game so that they gain the initiative for a number of moves and dictate the response of their opponent. In such a case, a player is said to have sente and the opponent to have gote. Sente usually occurs when players place their opponent in a situation of having to save stones and only having one option available to do so. Sente allows a player to control the course of the game so as to execute a plan of several moves without the opponent being able to frustrate the plan in midstream. 2.6 Ladders Ladders are a capturing race between a group that is almost enclosed, and a surrounding group. Consider the initial stones in Figure 12 (the stones without numbers). The black stone is doomed to be captured no matter what the Black player does. When White plays at 1, the black stone is threatened with capture. To defend this stone, Black plays at 2. White once again threatens capture by playing at 3. This process continues and results in a ladder being formed. White eventually wins the ladder when the board edge is encountered. 2.7 Links The only links between stones which is recognized in the rules of Go is between horizontally and vertically adjacent stones (called nobi). In practice however, there are several links which are recognized by experienced Go players (Figure 13). The ikken tobi link can be physically connected as long as black plays next. The kosumi link can be made as long as black plays next or each of the connecting points are empty if white plays first.

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