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Introduction and object of the board game
Go is a classic Oriental board game. The goal of the game is to possess as much of the board as possible, by surrounding it with your own stones. This board game has about as many players as chess; it is one of the most played board games in the world. In contradiction to chess, where the individual qualities and differences between pieces are most important, the go-stones get their power from number and cooperation.
Liberty
Both players place one stone on a crossing of lines. An important concept in the board game of go, are the "liberties". A separate stone with no neighbours has 4 liberties; these are empty pieces of field which are accessible through the lines (only vertically and horizontally, not diagonally). When two stones of the same colour are connected through a line, they form a "chain". Chains share their liberties, and are therefore connected to each other throughout the rest of the board game. Thus, two connected stones without neighbours have 6 liberties.
 
To strike
Stones and chains of the opponent can be beaten by taking the liberties of the chain. You do this by placing your own stones on the empty places around the chain; to surround them with your stones. Because a chain is sharing its liberties with all the stones, the chains can only be beaten as a whole, when none of the stones in the chain has liberty anymore.
The black stones can be beaten in 1 move
Suicide
It is not allowed to place a stone where there are no liberties anymore, if you don't strike a whole chain. However, you are allowed to strike a whole chain.
 
White: placing on the red point is suicide, placing on the blue point will kill a black chain.
Eyes
Eyes are areas that are surrounded by a chain, in which the opponent will not be able to place stones without being killed immediately. Therefore, this eye guarantees the liberty of a chain. Because of the suicide rule, you can kill a chain that has one eye, by placing your stone in the eye and taking the last liberty. When a chain has two eyes, you cannot place anything, because neither one of the eyes can be the last. A chain with two eyes can therefore never be taken of the board, no matter how many moves the opponent is allowed to do. A chain like this is called "alive". This is very important, because you can chain everything, and still let it be alive. (chains can only be struck as a whole).
 |  | | Black has one eye. The black chain has two eyes and is alive. |
Fake eye
Sometimes a position looks like an eye, because the field is surrounded by stones of one colour. However, the opponent can still ruin this eye because it is not surrounded by a chain. This means the eye is not e real eye.
The red spot is not a "real" eye. Black has got only one eye, and is not alive.
Ko
The "ko" rule prevents endless repetition of moves. It is not allowed to move exactly one stone, which has beaten you during the last move. This rule is automatically carried out by Brettspielnetz.de.
Example of the ko-situation. White can not immediately strike back.
After another move, when your opponent hasn't blocked the ko, you are allowed to strike back. Because of this, it might be handy to save all your moves, on which your opponent has to react. When he reacts to your move somewhere else on the board, you can strike the ko and then the other player is not allowed to strike back immediately.
To pass
When you think all moves would be useless because all the areas are within borders, you may pass. If both players pass, the board game is over and the counting phase begins. During this phase, the results of the board game will be calculated. This can be quite tricky.
When to pass?
It is correct to pass when for either side
there is no possibility to surround more territory
the status (dead or alive) of all stones is clear
there is no possibility to create a new living group anywhere
there are no gaps in the external boundaries of living territories
Placing a stone in this situation would at best gain zero points and at worst lose one point, because:
you reduce your territory by one point when you place a stone inside it that's not required for defense.
you increase your opponent's territory by one point when you place a dead stone inside it that doesn't force your opponent to defend by placing a stone inside it too.
So it makes no sense to keep placing stones in this situation. This means the game is finished and ready to be scored.
Some skill and scrutiny are required to judge correctly whether a game is finished and some skill may be required to prove your status judgement if your opponent challenges it. But when you are convinced you don't need to defend further and the game is finished, you should pass.
Comments on passing
Sometimes a player passes when the game is in fact not finished (he misjudges the current position). His opponent may take advantage of this mistake.
Sometimes a player keeps placing stones when the game is in fact finished. This happens when:
The player is a novice who hasn't read the rules or does not understand them.
The player misjudges the status of a particular group. As soon as he realises his mistake, he'll probably pass too (or resign).
The player knows the game is finished and lost, but hopes to reverse the outcome by luring his opponent into making a game losing mistake. The longer this behaviour persists, the more it is considered poor sportmanship. His opponent could pass whenever he can to gain free points, but he should also take care to defend when it is required.
Even though legal, it is undesireable that a player drags on a finished game for hundreds of moves, until he ultimately runs out of legal moves and is thus forced to pass and accept defeat.
Score
Your score is calculated by adding the following to each other: number of confined areas + number of imprisoned stones of the opponent + number of stones of the opponent that are still on the board but can be killed anytime ("dead stones"). This is explained later on. Also, White gets 6,5 points bonus to compensate Black's beginning advantage.
Dead chains
Dead chains are groups of stones that are still on the board, but can be beaten anytime, because they can never make 2 eyes. Stones like these don't have to be captured during the board game, because they will be automatically caught at the end of the game. Do not strike them if you don't really have to, because to be able to strike them you will have to put your stones in your own area, which will lower your score. Besides that, these moves are completely useless.
Ordinarily, dead groups are automatically detected by Brettspielnetz.de. However; there are so many complex situations possible, which can cause the automatic detection to make a mistake. In this case, it is possible to correct this yourself. If you don't really understand the concept of dead stones, it is advisory to agree with the automatic presentation. In 95% of the cases, this is correct.
The red marked stone will be removed at the end of the game. The black chain will have 2 eyes and will live.
The white stones are dead, the black stone in the middle makes it impossible for white to make 2 eyes.
Enclosed areas
After the dead stones have been removed, the area points are counted. One area is counted for you, when it is completely surrounded by your own stones. Only empty fields are counted; your own stoned do not count as points. So, do not move your own stones in an area that's already yours; it will make your area smaller and this will cost you points. Also, pay attention not to pass too quickly: if you have a huge enclosed area with a tiny hole in the wall, the whole area will not be counted!
White has surrounded 7 areas.
Seki
It is possible that a situation will occur in which two chains do not have two eyes, but still cannot kill each other without being killed themselves. In the example below, the player who will move in one of the two mid-areas first, will lose the whole chain. Therefore, none of the players move and the surrounded area is neutral.
The blue marked stones "live in seki".
Author: Vincent de Boer.
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