Some people like to offer quotations aimed at showing how superior go is compared to other games. For example, I heard one that goes, "Chess was invented, but go was discovered." Another has it that "if aliens wanted to play a game on Earth, it would be go."

Over the past 10 weeks, we have gone through the basic rules of the game. Let us go through these rules again. For the purpose of brevity, the diagrams contain multiple situations.

Diagram 1: Black plays the first move. He can place his stone wherever he wants, even in the corner.

Diagram 2: For a stone to survive, it needs liberties. The liberties are a stone's adjacent unoccupied spaces. Black A has two liberties, white B has three, black C has four, and white D has one liberty. A stone that has only one liberty is described as being in "atari."

Diagram 3: Stones can form a group and share liberties. The two black stones A have six liberties, the white group B has just one liberty, the white group C and the black group D have two liberties each, which they share.

Diagram 4: Stones with no liberties are dead and must be removed from the board. The black stone at A, for example, is dead.
If Black plays at 1, the white stones B lose their last liberty and are removed from the board. If White were to play at 2, he would put his C group stones in grave danger. He has only one liberty left. Black's stones at D also have one liberty left but he can take away White's last liberty by playing at 3.

Diagram 5: These are the respective situations after capturing the various stones.

Diagram 6: This is the ko situation. The marked black stone has only one liberty left--it is in atari.

Diagram 7: If it is White's turn, he can capture the marked stone by playing at 1.

Diagram 8: After removing the captured stone, the new situation looks like this. However, the marked white stone is now in atari. However, Black is not allowed to capture it immediately because the ko rule says that no full-board position can exist twice. Black, therefore, must play elsewhere and in such a way that White has to answer--this is called a ko threat--so that he can in turn capture the marked white stone, which brings us back to Diagram 6. White now must play elsewhere.

Solutions to last week's problems

Solution 1: White can play at 1 to start a ko. Black has no choice but to capture at 2 and hope he wins the ko. To do this, he needs to connect at 1 on his next move. If he loses the ko, his group in the corner will die.

Solution 2: Black's marked stones are in danger. His last resort is to start a ko by playing at 1. White will capture the ko first, but at least Black has a chance to free his stones.

Solution 3: The white invasion, starting with 1 through 5 is very common. However, it has some scary consequences. In response to black 6, White has to start a ko with 7.

Reference 1: After white 8, in Solution 3, White cannot capture right away and plays elsewhere with 9 (not shown). Black can then finish the ko by capturing the marked stone with 10.

Reference 2: Now imagine that Black does not finish the ko with 10 and decides to answer white 9. Then on the next move, White can capture the ko with 11 and if he ignores Black's next move 12 (not shown), he can capture the second marked stone with 13.

There is a great difference between the results in Reference 1 and 2. In Reference 1, Black takes the corner and builds outward influence as well. In Reference 2, however, White takes the whole corner and destabilizes the entire black group. Since the outcome of the ko often has such a great effect on its surroundings, it is important to understand a little about ko threats. We will discuss this next week. Find out more? Come to Ben's Cafe in Takadanobaba, Tokyo (Tel: 03-3202-2445 or www.benscafe.com), where the English-sp eaking go community congregates every Sunday starting at 11 a.m. You can enjoy free lessons until 1 p.m.

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