Tang Rules

Version 1, 2011-06-09

General

- The players alternate plays until agreement or overflow.
- A player's "play" places his stone on an empty intersection and then removes any opposing stones without liberty and adds them to the prisoners.
- "Equal Stones": The last play is undone if it creates an odd difference of numbers of black and white plays.
- A "road" is an empty intersection surrounded only by one player's stones.
- The player with a favourable score wins.

Scoring after Completion without Overflow

- "Completion" is the imagined filling of all empty intersections so that a player's plays fill his roads and empty intersections surrounded by both players' stones are filled by both player's plays.
- "Overflow" occurs when a player seeking completion transforms a string of his from uncapturable to capturable.
- Each player plays until completion without overflow.
- Subject to Equal Stones, the score is Black's minus White's number of stones on the board.

Counting without Completion

- The players stop alternating plays on agreement.
- Then those stones are removed and added to the prisoners that would be removed in completion without overflow.
- The group tax is Black's minus White's roads as if completion without overflow were used.
- The score is counted as Black's minus White's current roads plus white minus black prisoners minus the group tax.

Comments

- These rules are implied from Chen Zuyuan's history research summary The History of Go Rules and are Robert Jasiek's wording in modern rules language.
- In case of an equal score, the game is a tie.
- Either Black or White starts the game.
- Probably the basic ko rule applies.
- Probably the no suicide rule applies.
- If the last play is yose, there are no dame, counting without completion is used and the last play needs to be undone, then it is undefined how Equal Stones is achieved.
- Group tax applies to the remaining roads in (ordinary) sekis but not to the empty intersections surrounded by both players' stones.
- Playing an equal number of two-sided dame does not affect Equal Stones.
- Equal Stones cannot always refer to an equal number of plays but has to refer to an even difference of numbers of plays because it can happen that one player reaches overflow while the opponent still has to make more than one excess play before also reaching overflow. If the opponent's roads are all ponnuki shapes, then the player's invasions there could not work. It is unclear whether this circumstance was considered during the Tang Dynasty.
- Also when the players make an agreement to stop, Equal Stones has to be applied.
- Hopefully the counting without completion determines the score after completion without overflow. A proof should be provided.

These rules describe a territory style stone scoring.
It starts with normal stone scoring which corresponds area scoring minus group tax and then uses the equal-stones rule to transform between area and territory style scoring(both with group tax). So the end result corresponds to territory scoring minus group tax. (Disregarding very exotic situations).

Is this interpretation correct, or did I miss something?

_________________
Sanity is for the weak.

Unless some pass fight trouble exists, your description more or less gets it. Within the rules, it is not a transformation from area scoring though but from stone scoring. (I guess you are aware that the group tax changes middle game strategy because connecting groups is worth an endgame bonus.)

- "Equal Stones": The last play is undone if it creates an odd difference of numbers of black and white plays.

not sure i understand this rule.
let's take the first move on the board. so far, 1 player played 1 move while the other played 0 moves. 1-0 = 1, an odd number. therefore the first move is always removed? now let's say the opponent played a move. the total number of moves for both sides is 1, although player 1's first move was removed. therefore player 2's move doesn't get removed? and when player 1 plays again, he creates another odd difference.

i assume you really mean an odd difference as in more moves for one player than the other, and not opponents turn.
this really is only a concern then near the end of the game with passing.
like aga rules, if player 1 passes first, then player 2 passes, everything is fine.
but if player 2 passes first, and player 1 passes, player 2 needs to pass again.

@phillip1882:

It is the "last" play that is undone, not the "latest", so this only applies when all plays of the game have been made (i.e. when it is finished).

there is no group tax in Tang rule ,because it immédiatly count the roads whthout two eyes for every stone group.group tax appeared about Ming ，to be part Ming and Ching rule