...Just the opposite. White marked stone is in Atari and black can suicide and capture it. Well, if both black and white keep capturing each other the game will never end. So THE RULE IS: IT IS FORBIDDEN TO RECAPTURE A KO IMMEDIATELY! It means that black (in our case) has to wait at least one move until he can capture the Ko. "Waiting" means actually to play somewhere else. If white answers that move black can capture the Ko...if he wants to. We call this a "Ko threat" a move bigger than the Ko itself so the opponent will have to answer it. The one with more Ko threats will eventually win the Ko but the other will still play two moves somewhere else so we have to be very careful when fighting a Ko.

  Here we have two different kinds of Ko. Black can capture one and white-the other, or black can FINISH one and white the other. To FINISH a Ko means to simply connect the stone in Atari with the others and the Ko disappears. A Ko can be worth more than one stone so we have to be careful which Ko we finish.

  This time we have a triple Ko: one in the corner, one in the middle, and one on the right side. If black captures in the corner, white takes in the middle and black captures on the side, then white can return to the corner and recapture (one move passed since black played there!) but black will recapture in the center then white on the side and so on...Well, by doing this the game will never be finished but there is a rule about it. Capturing and recapturing a triple Ko will let return the board to the same position. IF THE WHOLE BOARD POSITION WILL BE REPEATED THREE TIMES THE GAME WILL BE STOPPED AND CONSIDERED A DRAW. There are cases when both players are forced to make a draw because of the values involved in the Ko but during a game many small Ko will appear and the players must fight only the important ones.

  Now about SEKI. A SEKI IS A POSITION IN WHICH SURROUNDED GROUPS ARE ALIVE BECAUSE OF COMMON LIBERTIES. Take a look at this first. Both black and white marked groups are surrounded but there are two common liberties left. If black takes one of these liberties he will be left in Atari and white to move so white will capture black. That means black better don't play...If white plays and take one common liberty then black will capture white. The conclusion is that neither black or white will like the prospect of taking the common liberty so nobody will capture nobody. In a Seki we will consider the common liberties as neutral points so zero points for both players. Seki and ko are very difficult situations and the differences between different rules (Japanese, Chinese, Ing and so on) are sensible around these matters.

  Black 1 here is a mistake and white is safe now being impossible to be killed.

If black plays like this...

  ... A ko will start. In conclusion: white can't play so for him it looks like a seki, while black can start a Ko. Under the japanese rules the WHITE GROUP IS DEAD! because black can start the ko any time so he can protect against white ko threats (though HE DOESN'T NEED TO ACTUALLY DO IT!) then kill white. Please observe that white has to find the first Ko threat. Under all other rules white is dead as well. The sequence in this corner involves a little bit of practice so please try to figure out by yourself other variations.