Dame Under Area Scoring

   

If someone could verify/clarify the contents of this page that would be much appreciated. If it is correct then this should also be linked to from half-point ko, area scoring and perhaps ko-threat.

 --Jono

Table of contents Table of diagrams
Black to move: Black is dame-master
Example: Even dame
Example: Odd dame

Under rules that use area scoring (such as Chinese, Ing, AGA, New Zealand) locations that are refered to as dame are often worth points.

Definition: Dame

For the purposes of these pages, a dame under area scoring is an empty location on the board which, if played by either player, would be worth 2 points in gote (deiri counting) to that player.

Dame-Master

[Diagram]

Black to move: Black is dame-master

The dame-master is the player who has the right to the final dame on the board.

Checking whether you are dame-master on your move is trivial: if there is one dame left, then you are dame-master. If there are two dame left, your opponent is dame-master. Through simple induction, if it is your move and there are an odd number of dame, then you are dame-master.

In an even game, when the dame-master also plays the first dame, no player has passed, and there is no seki, territory scoring and area scoring differ by one.

Jono: I thought the difference in seki scores was only because Japanese rules didn't count eyes in seki. If this "feature" didn't exist wouldn't the seki values be the same under both scoring methods?



Dame and Half-point Kos

At the end of a game there is often a final half-point ko to be played out. By miai counting a half-point ko is worth 1 1/3 of a point, and dame 1, so it is normally best to fight the ko if possible rather than filling dame. (It is always best to take the ko, but sometimes better to fill a dame rather than win the ko.)

Case 1: Last Dame

When there is only one dame remaining it is simple, fight and win the ko if you are ko-master, otherwise take the dame.

Case 2: Even Dame

When there are an even number of dame and one half-point ko, you once more wish to fight the ko. However, the opponent can use dame as ko threats, since if you fill the ko you will no longer be dame-master. If this means you are no longer ko-master, dame should be played, until your opponent is forced to connect the ko.

Case 3: Odd Dame

When there are an odd number of dame and one half-point ko, even if your opponent plays a dame point, you can fill the ko and remain dame-master.


Example 1

[Diagram]

Example: Even dame

If black had two external ko threats and white none, black can win the ko and take two dame. Giving black 4 of the contested points.

If black has only one external ko threat, the best he can do is to play a dame ko-threat, which white will ignore to connect the ko. This gives black 3 of the dame points.

If white has three more external ko threats than black, she does not need to ignore any of black's dame ko-threats, and black gets only 2 of the contested points.


Example 2

[Diagram]

Example: Odd dame

If both black and white have no external ko threats, black can take and fill the ko and still take 2 dame. Giving black 4 of the contested points.

If black has no external ko threats and white one, black can only take 3 dame.


This is a copy of the living page "Dame Under Area Scoring" at Sensei's Library.
(OC) 2009 the Authors, published under the OpenContent License V1.0.
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