Ikeda Area III Rules


The Ikeda Area III rules are one of the rulesets proposed by Ikeda Toshio

The nice things about this ruleset is that it combines the granularity of territory scoring with the ease of area scoring (although not everybody agrees with this)

the rules of all Ikeda rule sets can be found at [ext] http://gobase.org/studying/rules/ikeda/e_rules.html

The Ikeda Area III rules are:


Definitions (1)

n x n go board
A grid comprising n equally spaced parallel lines and n other parallel lines orthogonally intersecting them is called an n x n go board.
grid line
The parallel lines that intersect orthogonally on the board are called grid lines.
grid point
The points of intersection of grid lines are called grid points.
empty grid point
A grid point not occupied by a stone is called an empty grid point.
occupied grid point
A grid point occupied by a stone is called an occupied grid point.
played stone
A stone occupying a grid point is called a played stone.
adjacent points
On the grid lines incident with a given grid point, the grid points closest to that grid point are called the adjacent points of that grid point.

Definitions (2)

To play means to place a stone on an empty grid point.
To remove means to remove a played stone from a grid point.
To move means to play or pass.
To pass means to proceed to the next turn without playing.

Definitions (3)

removable state
A set of played stones of the same color is said to be in a removable state if all grid points that are not occupied by the set, but are adjacent points of grid points occupied by the set, are occupied by played stones of the other color.

Definitions (4)

The arrangement of all played stones on the board is called a configuration.

Definitions (5)

If continued motion on the grid lines in a set of empty grid points, starting from any grid point in the set, always leads to played stones of the same color, that set of empty grid points is said to be territory of that color, and those played stones are said to surround that territory.


(only the rules of the area III rules are mentioned here)

Rule 1 Black and white stones:

One of the two players possesses black stones; the other player possesses white stones. The players play stones of their own possession.

Rule 2 Rule of alternate moves:

The players move alternately. A player who fails to move loses.

Rule 3 Rule of removing:

When a stone has been played, if a set of stones of the other color is in a removable state, that set of played stones is removed before the next move.

Rule 4 Rule prohibiting repeated configurations:

If playing on a grid point places any stones of the other color in a removable state, the configuration resulting from removal of those stones must not be identical to a configuration that has already appeared in the game.

Rule 5 Rule prohibiting self-capture:

If playing on a grid point does not place any stones of the other color in a removable state, the played stone itself must not be in a removable state.

Rule 6 End of the game: (special Area III rule)

After the first pass, the game ends when both players pass in succession.

Rule 7 Rule of scoring: (Special area III rule also known as the Ikeda's rule)

A player's score is the number of that player's played stones plus the number of grid points in that player's territory. If the first pass was made by White, however, then 1/2 point is subtracted from Black's score and added to White's score. The winner is determined by comparing the players' scores.

Rule 8 Rules establishing conditions of play:

Separate rules may be made concerning the first move (e.g. handicap stones) and determination of the winner (komi).

Notes by Ikeda Toshio (Part of the rules)

Area rules III adjust the score by one point when White passes first. This eliminates the one-point difference between area and territory rules that arises about half the time in even games from Black's having played an extra stone.

By having the players compete to be first to pass, territory rules I and area rules III introduce an element of skill not found in traditional territory or area rules. Territory rules III and area rules II avoid introducing this new element.

None of these rules make any provision for removing dead stones without further play at the end of the game. As Ikeda mentions in Part II, however, this can be done by mutual agreement after both sides have passed.

Explanations by Ikeda

Ikeda explains these rules at:

[ext] http://gobase.org/studying/rules/ikeda/?sec=e4010000 and following pages

More comments and explanations:

The only 2 special rules in this rule set are rule 6 and rule 7

Rule 6 End of the game: This is a rather complex rule: the game ends with 3 passes if the first (bonus) pass is not followed by a play) and with 2 passes if it is.

Ikeda does not give an explanation for this rule.

It seems likely that it is that he doesn't want to give the opponent of the player that makes the first pass the option to end the game directly after the first pass. If this player also passes the first passer has the option to continue the game by making a play.

Rule 7 Rule of scoring: For commenta on this rule see the comments at Ikeda's Rule

See also:

Nobrowser?: Rule 6 seems to make a difference if there is a one-sided dame (OSD) point. The player in control of that point can pass (and collect the first-to-pass bonus), knowing that a pass by the opponent will not end the game but allow another opportunity to fill the OSD, which in area scoring counts as a full point.

Also, Rule 6 together with Rule 7 is exactly equivalent to the Button rule (with integral komi). Without Rule 6, it wouldn't be, because taking the Button doesn't count as a pass, per its inventors.

Ikeda Area III Rules last edited by on March 27, 2023 - 19:37
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