Backgammon (GM[6])

For more information contact Gary Wong (author of Gnu Backgammon) at gary@cs.arizona.edu.

Point & Stone type

In Backgammon, the Stone becomes Point, and is a single lower case letter.

[coordinates (bgpoint.png)] Coordinate system for points and moves

`a' is the 1 point for white (and the 24 point for black), through to `x' which is the 24 point for white (and the 1 point for black). `y' is the bar, and `z' is the bearoff tray.

Move type

Normal moves specify the dice roll (as a pair of digits from 1 to 6) followed by 0 to 4 source/destination pairs. Moves which hit are not recorded differently.

Other legal moves include `double', `take' and `drop' for cube action (where `double' includes initial and subsequent doubles, as well as beavers).

Examples of legal moves include:

W[31hefe]: White playing an opening 31 as 8/5 6/5.
B[61yg]: Black entering with bar/18.
B[66]: Black failing to enter with 66.
W[66fzezdzcz]: White rolling 66 and playing 6/off 5/off 4/off 3/off.
W[double];B[double];W[take];W[66fzfzfzfz]: White doubles, black beavers, white accepts the beaver and rolls 66 to play 6/off(4).

Colours

The specification describes players as "black" and "white"; if an implementation uses alternate names, then the following defaults are recommended for consistency:

 White = O = 0
 Black = X = 1

Properties

Property:	CO
Propvalue:	simpletext
Propertytype:	setup
Function:	Set the position of the doubling cube.  The value
                should be `b' (black), `w' (white), `c' (centred), or `n'
		(none -- for cubeless or Crawford games).
Related:	CV

Property:	CV
Propvalue:	number
Propertytype:	setup
Function:	Set the value of the doubling cube.  This value
                defaults to 1 at the beginning of the game, but a CV property
		should be added when setting up a position where a double has
		been made, or at the beginning of a money game if automatic
		doubles occur.
Related:	CO

Property:	DI
Propvalue:	number
Propertytype:	setup
Function:	Set the dice without moving (this could be useful for
		creating problem positions, e.g. DI[31])
Related:	CO

Property:	MI
Propvalue:	list of composed simpletext ':' simpletext
Propertytype:	game-info
Function:	Specifies information about the match the game belongs to.
		This property should specify a list of tag/value pairs, where
                the allowable tags are case-insensitive, and include:

                  length - the match length (number of points); value should
                           be a number
                  game   - the number of this game within the match (the
                           first game is 1); value should be a number
                  bs     - the score for Black at the start of the game;
                           value should be a number
                  ws     - the score for White at the start of the game;
                           value should be a number

                Unknown tags should be ignored (a warning may be produced).
                The order of tags in the list is not significant.  An example
		MI property is:
		                  MI[length:7][game:3][ws:2][bs:1]
Related:	EV, GN, RE, RO

Property:	RE
Propvalue:	simpletext
Propertytype:	game-info
Function:	The general RE property has the following
                modification in backgammon games: in the case of a
                resignation, the value should also specify the number of
                points before the R(esign).  Here are three example RE
                properties:

                        RE[B+6R]      -- White resigns a backgammon on a 2
                                         cube (worth 6 points).
                        RE[W+2Resign] -- Black resigns a gammon on a 1 cube
                                         (worth 2 points).
                        RE[W+4]       -- Black drops a redouble to 8 (note
                                         this is considered a normal loss, not
                                         a resignation).
Related:	RE

Property:	RU
Propvalue:	simpletext
Propertytype:	game-info
Function:	Backgammon-specific values for the general RU property
                include the following:

		  [Crawford] -- the Crawford rule is being used in this match,
		    although this is not the Crawford game.
		  [Crawford:CrawfordGame] -- this IS the Crawford game.
		  [Jacoby] -- the Jacoby rule is in use for this game.
Related:	RU