Atari Go Counting
Atari Go Counting
Atari-go is a go variant, where the first player to capture any stones instantly wins the game.
Usually a game of atari-go is played to the bitter end, so that if no stones are captured before the territories are settled, players play the dame, and then add stones to their own territories until one of the players will be forced to put some of his own stones into atari.
Counting territories
Counting points in atari-go is done very much the same way as in normal go. [1]
At this point of the game, all the territory is settled. Black has 7 points of surrounded territory, white has 6. As the players play inside their territories, white will be the first to put himself in a self-atari, so black will win, if he plays with a correct strategy.
Seki
On this board, there are two independent sekis. The sekis count as zero points for both, so the next player to move will lose, because only self-atari moves are available.
Group tax
Because every group needs two liberties to avoid capture (in atari-go they don't even have to be in separate eyes), having more groups costs some of the points as group tax.
Here white has two groups against black's one. As you can see, black can play one more move without putting himself in atari, after which white is forced into playing self-atari.
"Square tax"
A surprising feature of atari go is that the square shape in this diagram counts as zero points for white. This happens when the white group does not have another eye elsewhere.
Even though black originally had no move inside the white square, after black can play
to turn white's group into a seki. White is forced to playing a self-atari on his next move.
The square tax seems to be two points, just like the group tax. Because a group with a two point eye is worth zero (2 points minus group tax), and a group with a single square eye is worth zero (4 points minus group tax and the square tax), here it does not matter whether white plays a or b.
If white chooses to play b, he gets rid of the square (or, "pays the square tax"), but black a will force white to play inside his own territory once more, so the price was two points anyway.
Other interesting bits
Bass could not come up with any more strange atari-go scoring quirks, so add yours here!
[1] RobertJasiek: Why? Pass-fights are possible and can let "scores" be fake predictions! Oops, now I get it: One needs a proof that pass-fights would require captures, and in atari go, they can't occur prematurely.