“The Japanese game of Go is of interest both as a problem in mathematical representation and as a game which generates a move tree with an extraordinarily high branching factor (100 to 300 branches per ply).

“The complexity of Go (and the difficulty of Go for human players) is thought to be considerably greater than that of chess. The constraints of being able to play a complete game and of being able to produce a move with a moderate amount of processing time were placed on the solution. The basic approach used was to find methods for isolating and exploring several sorts of relevant subsections of the global game tree. This process depended heavily on the ability to define and manipulate entitles of Go as recursive functions rather than as patterns of stones.

“A general machine-accessible theory of Go was developed to provide context for program evaluations. A program for playing Go is now available on the Stanford PDP-10 computer.”

– Heuristic Analysis of Large Trees as Generated in the Game of Go, by Jonathan Leonard Ryder, Department of Computer Science, Stanford University, 1971

Onnanoko playing “go”, c. 1910.

“Go reached Japan in the 7th century CE. The game soon became popular at the Japanese imperial court, and among the general public by the 13th century. The game was formalized in Japan in the 15th century CE.

“In 1603, Tokugawa Ieyasu re-established Japan’s unified national government. In the same year, he assigned the then-best player in Japan, a Buddhist monk named Nikkai, to the post of Godokoro (Minister of Go). Nikkai took the name Honinbo Sansa and founded the Honinbo Go school. Several competing schools were founded soon after. These officially recognized and subsidized Go schools greatly developed the level of play and introduced the dan/kyu style system of ranking players. Players from the four schools (Honinbo, Yasui, Inoue and Hayashi) competed in the annual castle games, played in the presence of the Shogun.

“Despite its widespread popularity in East Asia, Go has been slow to spread to the rest of the world. Although there are some mentions of the game in western literature from the 16th century forward, Go did not start to become popular in the West until the end of the 19th century, when German scientist Oskar Korschelt wrote a treatise on the Japanese game.

“In 1996, NASA astronaut Daniel Barry and Japanese astronaut Koichi Wakata became the first people to play Go in space.”

– Wikipedia