Go is such a difficult game ...

By Rob Van Zeijst

Go is such a difficult game to crack because of the vast number of possible positions that it is frequently used in studies of artificial intelligence. No wonder players feel the need to limit the number of their possibilities on the board. This can be done by making forced exchanges, which would be reasonable if you are ahead and want to settle the game in your favor. At the same time, playing out all your options simplifies the game for your opponent, which is called aji keshi, and puts him at ease. If you leave your options open though, it will keep your opponent off balance and may lead to a quick victory.

The following game is the second in the best-of-five Women's Honinbo title match between Kaori Chinen (White), current female Honinbo, and challenger Kumiko Yashiro (Black). The challenger won the first game by 1-! points. In this game Black commits a grave blunder by playing aji keshi.

Diagram 1: In the opening, Black sets up a large-scale framework through 13, which was followed by White's invasion at 14. Both sides display a lot of fighting spirit in the sequence through 23. The moves 24 to 32 are more or less forced, but black 33 is a bad move (see Reference 1). This also led to Black's next blunder, move 37. The exchange 37 for 38 does not reinforce Black's position much and it enables White to cap at 40. Black resists with 45, but because she failed to exchange A for B, White hit her hard in this area. We will see how next week.

Reference 1: Black 1 (33 in Diagram 1) allows white 2 to repair her defects. In addition, white 2 restricts the liberties of Black's marked stones. For example, if Black plays 5 straight away (without exchanging 9 for A as in the game), White can cut with 6. However, Black has no problem in sacrificing these stones with 9 through 17, because White's marked stones are weakened significantly. This is a good result for Black.

Reference 2: Instead of first exchanging black A for white B, Black should have played at 1 immediately. Black can later play at 5, threatening to capture white 2. By avoiding the exchange C for D (as in the game), Black's marked stones are not nearly as weak.

Reference 3: Without the exchange A for 4, White can capture the marked stone by cutting at 1. If White tries to escape with 2, black 3 is sente and White has to defend with 4 (or B), allowing Black to capture White in a ladder up to 11.

Hints for improving your game

Playing out a position while reducing possibilities is usually not a good idea. Let's see why.

Diagram 2: The moves through 14 are a joseki, a standard corner exchange. There is no need to add moves at this point.

Diagram 3: What happens if White plays at 1? To protect against the cut, Black has to defend somewhere. What do you think when you see the 2-for-3 exchange before Black defends at 4? All too often, beginners believe a sente exchange--a move that has to be answered--is automatically a good move.

Diagram 4: If Black immediately defends without the exchange A for B, he may be able to pull out his stone with 1, while threatening the marked white stones.

Solutions to last week's problems

Solution 1: As we discovered last week, White has to be careful. After pushing Black down once with 1, he should defend his cutting point with 3. Black connects with 4 and White pushes Black down again with 5. Later he can aim at the cut at A by playing at B, C, or D.

Solution 2: White 1, 3 and 5 make optimal use of the threat the marked white stones pose. Even after black 6, these stones have potential. Since A is sente, Black cannot pull his marked stones out after white 9. Black is reduced to making life on the side. White ends up with a lot of center thickness and starts a new attack with 31.

New problems

Problem 1: The moves through 11 are a joseki. The stone at 2 still has potential. White 12 threatens A so the moves through 17 are forced. White can play at 18 to exploit the potential of white 2. But what is he really aiming at?

Want to find out more? Come to Ben's Cafe in Takadanobaba, Tokyo (03) 3202-2445 where the English-speaking go community congregates every Sunday. You can enjoy free lessons, 11 a.m.-1 p.m. Ben's Cafe can be accessed at www.benscafe.com.

Van Zeijst is a four-time European go champion and European representative at the Fujitsu World Championship.