The Magic of Go

Meijin title match

On Nov. 12, Cho Chikun defended his Meijin title by winning the seventh game and defeating O Rissei 4—2 in the best-of-seven match with one game ending without result. With this victory, Cho has maintained his dominance over the three top Japanese go titles: Kisei, Meijin and Honinbo.

O Rissei is one of the top players in Japan. He has had especially good results this year. In March, he won the LG Cup, a major international tournament sponsored by the South Korean LG Group. Then, in May and June, he challenged Cho for the Honinbo title (he lost 4—2). In August he swept the Meijin league with eight straight wins to become the Meijin challenger. He is also the challenger for the Oza title, one of the big seven open titles.

O was born in Taiwan in 1958 and, like Cho, came to Japan to pursue a career as a professional go player. He became a professional at the age of 14 and attained the highest rank of 9-dan in 1988. Over the years, he has won numerous titles, but it is only in the last three years or so that he has come into his own. His go is much admired by his fellow professionals, and he has created many new moves in the opening.

Both Cho and O play tight territorial games as opposed to an influence-oriented strategy. But, in their games with each other, Cho seems to be able to force O to play for influence, which goes against his nature. This is one of the hallmarks of Cho’s strength: he does not let his opponents play the way they want.

The title match this year was especially noteworthy because the fourth game ended with a no-result, the first time this has happened in a major title match. This requires an explanation.

Draws never occur in tournament games because of the «komi» system, which evens up the contest. Since it is estimated that making the first move is worth about five to six points, the player with Black (who makes the first move) gives the player with White 5 1/2 points.

At the end of the game, these extra points are added to White’s territory. Therefore, after the game is counted, one side will have at least half a point more than the other side. The only way that a result other than victory or defeat can occur is if some sort of impasse develops in the game.

One of the official rules of the Japan Go Association states that if the same whole-board position is repeated during a game, and the players refuse to stop this repetition, the game ends without result.

Here is what happened in the fourth game. Early in the game, one of O’s groups got into trouble, but it succeeded in living because, if Cho attacked it, it could live by creating a double ko. However, another ko developed in another part of the board later in the game. Cho felt that he might lose by half a point, so he attacked O’s group and O had to defend by turning the position into a double ko. There were now three active kos on the board. If either side lost one of these kos, he would lose the game. Thus, neither side could yield, and, eventually, the whole-board position repeated itself, so the game was declared no-result.

It is extremely rare for a game to end with no result, but, interestingly, this was the fourth time in Cho’s career that one of his games ended in a no-result.

Double ko

Let’s look at the double ko that occurred in the fourth Cho-O game. O was White. Diagram 1 shows the position after 98 moves. The white group in the middle of the left side is alive. It has one eye at A and can easily get another eye at B.

Go rules

If Black plays 1 in Diagram 2, White defends with 2. Black captures the marked stone with 3, threatening to capture the stone to the right of 1. But White captures the stone at 1 with 4. If Black connects where the marked stone was, White will connect at 1 and he now has two eyes for his group at A and B (see Diagram 1)

Suppose Black tries to fight the ko around 1 by making a threat elsewhere. If White answers this threat, Black can come back and capture the stone at 4, but White will play the other ko by capturing the stone at 3.

As you can see there are two kos here, and, for Black to kill the white group, he has to win both kos-the one around 1 and the one around 3. But this is impossible, so the white group is unconditionally alive.

However, when a third ko occurred later in the game, the stability of this position was upset. In our next installment, we will show the final position that led to the no-result.