Ultimate Go

The Go ruleset presented below has two main characteristics:

(i) It is very simple - the only non-trivial concept which is explicit in the rules is the one of "capture", reffered to as removal of "surrounded" stones from the board. All other concepts (including "score", "territory", "counting phase", "alive", "seki", "dame", etc.) are implicit from an analysis of the ruleset, not explicit in the rules. In other words it is a concise "axiomatization" of Go.

(ii) It solves the "free teire" issue, i.e. at the end of a tight game players will not get to play a reinforcement move "for free", without affecting the "score" at all. The simple solution via the device of an "ultimate stone", which signals the transition to an unofficial "counting phase", introduces only a slight complication to the rules.

An analysis of this ruleset (or rather of an older, equivalent version of this ruleset) can be found here: Analysis of Ultimate Go.

Ultimate Go rules

0. Ultimate Go is a game played between two players, Black and White. Each player has an endless supply of identical stones of her color, and a prisoner bowl.

1. The board consists of 19 horizontal and 19 vertical lines, and the stones are placed on their 19*19 intersections.

2. A stone on the board is said to be surrounded if there is no connected path along the lines from that stone to an empty intersection which avoids all opponent stones.

3. Before the game starts the board is empty, and each player puts exactly one of her stones in her opponent's prisoner bowl. Players move alternately, Black moving first.

4. A placement consists of a player placing a stone from her supply on an empty intersection, then checking which opponent stones are surrounded, and if such stones exist - removing all of them from the board to her prisoner bowl.

5. A placement is legal if the placed stone is not surrounded in the resulting board position, and furthermore that board position has not occurred in the game.

6. A delay consists of a player returning one of her prisoners (i.e. an opponent stone from her prisoner bowl) to her opponent’s supply. In the first delay of the game the delaying player should place her prisoner in her opponent's prisoner bowl (instead of his supply), and that stone is henceforth called the ultimate stone.

7. A move consists of either a legal placement or a delay.

8. A player may declare a draw if her opponent's prisoner bowl contains only the ultimate stone.

9. At a player’s turn she must do one of the following: make a move; declare a draw, in which case the game ends with a draw; resign the game, in which case her opponent wins.

• Note that only the player who was first to delay can declare a draw, and she can do so only if her opponent has no prisoners, so in particular he delayed at least once.

— Yoav Yaffe

Discussion:

1.

RobertJasiek: Are there pass fights?

YoavYaffe: There are no pass fights in Ultimate Go, at least not in the classic sense (e.g. the AGA example in the Pass fight). The reason is that, unlike a pass, a delay (in Ultimate Go) does not participate in any game ending mechanism. It is true that in correct play the first delay (which will be an ultimate delay) roughly signifies the beginning of the "counting phase", but that phase transition has no official status in Ultimate Go, and game continues as usual (in particular the game "remembers" who delayed first). See more details in Pass fights in Ultimate Go.

However, in examples like Molasses Ko the relevant property of a pass is that it does not change the board position, and this property is shared by a delay. Hence a decisive Mollasses Ko in Ultimate Go will have similar results (i.e. a de-facto no-pass-Go game will ensue).

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