   #copyright

Backgammon

2007 Schools Wikipedia Selection. Related subjects: Games

                               Backgammon
   A modern backgammon set, consisting of a board, two sets of 15
   checkers, two pairs of dice, and a doubling cube
       Players      2
      Age range     5+
      Setup time    10–30 seconds
     Playing time   5–30 minutes
   Rules complexity Medium
    Strategy depth  High
    Random chance   Medium (Dice)
   Skills required  Strategy, Probability

   Backgammon is a board game for two players in which pieces are moved
   according to the roll of dice and the winner is the first to remove all
   his pieces from the board. Many variants have developed throughout the
   world, but most share the same common elements. It is a member of the
   tables family of games.

   The game is essentially a race, and luck plays a measurable role, but
   backgammon offers a significant scope for strategy. With each roll of
   the dice, a player must choose between numerous options for moving the
   checkers, and plan for possible counter-moves by his opponent.
   Opportunities for raising the stakes of the game introduce more
   strategic intricacies. Players have developed a vocabulary for common
   tactics and occurrences.

   Like chess, backgammon has been studied considerably by computer
   scientists. Research has resulted in backgammon software that is
   capable of beating world-class human players.

History

   Game recovered from the Vasa, sunk in 1628
   Enlarge
   Game recovered from the Vasa, sunk in 1628

   The ancient Egyptians played a game called senet, which resembled
   backgammon, with moves controlled by the roll of dice. The Royal Game
   of Ur, played in ancient Mesopotamia, is a more likely ancestor of
   modern tables games. Recent excavations at the " Burnt City" in Iran
   showed that a similar game existed there around 3000 BC. The artifacts
   include two dice and 60 pieces, and the set is believed to be 100 to
   200 years older than the sets found in Ur.

   The ancient Romans played a number of games with remarkable
   similarities to backgammon. Ludus duodecim scriptorum ("game of twelve
   lines") used a board with three rows of 12 points each, and the pieces
   were moved across all three rows according to the roll of dice. Not
   much specific text about the gameplay has survived. Tabula, meaning
   "table" or "board", was a game mentioned in an epigram of Byzantine
   Emperor Zeno (AD 476–481). It was similar to modern backgammon in that
   a board with 24 points was used, and the object of the game was to be
   the first to bear off all of one's checkers. Three dice were used
   instead of two, and opposing checkers moved in opposite directions.

   In the 11th century Shahnameh, the Persian poet Ferdowsi credits Burzoe
   with the invention of the tables game nard in the 6th century. He
   describes an encounter between Burzoe and a Raja visiting from India.
   The Raja introduces the game of chess, and Burzoe demonstrates nard,
   played with dice made from ivory and teak.

   The jeux de tables, predecessors of modern backgammon, first appeared
   in France during the 11th century and became a frequent pastime for
   gamblers. In 1254, Louis IX issued a decree prohibiting his court
   officials and subjects from playing the games. Tables games were played
   in Germany in the 12th century, and had reached Iceland by the 13th
   century. While it is mostly known for its extensive discussion of
   chess, the Alfonso X manuscript Libro de los juegos, completed in 1283,
   describes rules for a number of dice and tables games. By the 17th
   century, tables games had spread to Sweden. A wooden board and checkers
   were recovered from the wreck of the Vasa among the belongings of the
   ship's officers.

   In the 16th century, Elizabethan laws and church regulations had
   prohibited playing tables, but by the 18th century backgammon was
   popular among the English clergy. Edmund Hoyle published A Short
   Treatise on the Game of Backgammon in 1743; this book described the
   rules of the game and was bound together with a similar text on whist.
   The game described by Hoyle is, in most respects, the same as the game
   played today.

Name

     * In English, the word "backgammon" is most likely derived from
       "back" and Middle English "gamen", meaning "game" or "play". The
       earliest use documented by the Oxford English Dictionary was in
       1650.
     * In Arabic, the game is called tawilat el-nard (طاولة النرد) or
       tawilat el-zahr (طاولة الزهر), meaning "board of dice".
     * In Chinese, the game is called shuang lu (双陆), meaning "double
       sixes".
     * In Greek, it is referred to as portes and is played as one of the
       three games in a tavli match.
     * In Hebrew, it is called shesh besh (שש בש), derived from the
       Persian and Turkish for "six" and "five"
     * In Japanese, sugoroku (双六) refers to backgammon as well as other
       racing games.
     * In Persian, backgammon is called takhte nard, meaning "battle on a
       wooden board".
     * In Portuguese, backgammon is called gamão.
     * In Romanian, backgammon is called table.
     * In Turkish, the game is called tavla.

Rules

   The objective of backgammon is to move all of one's own checkers past
   those of one's opponent and then remove them from the board. The pieces
   are scattered at first and may be blocked or hit by the opponent.
   Because the playing time for each individual game is short, it is often
   played in matches, where victory is awarded to the first player to
   reach a certain number of points.

Setup

   Each side of the board has a track of twelve long triangles, called
   points. The points are considered to be connected across one edge of
   the board, forming a continuous track analogous to a horseshoe,
   numbered from 1 to 24. Each player begins with two checkers on his
   24-point, three checkers on his 8-point, and five checkers each on his
   13-point and his 6-point. The two players move their checkers in
   opposite directions, each from his own 24-point toward his 1-point.
   Path of movement for blue and green; checkers are in starting position
   Enlarge
   Path of movement for blue and green; checkers are in starting position

   Points 1 to 6 are called the home board or inner board, and points 7 to
   12 are called the outer board. The 7-point is referred to as the bar
   point and the 13-point as the mid point.

Movement

   At the start of the game, each player rolls one die, and the player
   with the higher number moves first. The players then alternate turns,
   rolling two dice at the beginning of each turn.

   After rolling the dice a player must, if possible, move checkers
   according to the number of pips showing on each die. For example, if he
   rolls a 6 and a 3 (noted as "6-3") he must move one checker six points
   forward, and another checker three points forward. The same checker may
   be moved twice as long as the two moves are distinct: six and then
   three, or three and then six, but not all nine at once. If a player
   rolls two of the same number (doubles) he must play each die twice. For
   example, upon rolling a 5-5 he must move four checkers forward five
   spaces each.

   A checker may land on any point that is either unoccupied or is
   occupied only by a player's own checkers. It may also land on a point
   occupied by exactly one opposing checker; such a lone piece is called a
   blot. In the latter case, the blot has been hit, and is placed in the
   middle of the board on the bar, the divider between the home boards and
   the outer boards. A checker may never land on a point occupied by two
   or more opposing checkers, thus, no point is ever occupied by checkers
   from both players at the same time.
   Medieval players, from the 14th century Codex Manesse
   Enlarge
   Medieval players, from the 14th century Codex Manesse

   Checkers placed on the bar re-enter the game through the opponent's
   home field. A roll of 2 allows the checker to enter on the 23-point, a
   roll of 3 on the 22-point, etc. A player may not move any other
   checkers until all of his checkers on the bar have first re-entered the
   opponent's home field.

   When all of a player's checkers are in his home board, he must bear
   off, removing the checkers from the board. A roll of 1 may be used to
   bear off a checker from the 1-point, a 2 from the 2-point, etc. A die
   may not be used to bear off checkers from a lower-numbered point unless
   there are no checkers on any higher points.

   If one player has not borne off any checkers by the time his opponent
   has borne off all fifteen, he has lost a gammon, which counts for
   double a normal loss. If the losing player still has checkers on the
   bar or in his opponent's home board, he has lost a backgammon, which
   counts for triple a normal loss.

Doubling cube

   Backgammon set, 19th century
   Enlarge
   Backgammon set, 19th century

   To speed up match play and to provide an added dimension for strategy,
   a doubling cube is normally used. The doubling cube is a 6-sided die
   marked with the numbers 2, 4, 8, 16, 32 and 64. If a player believes
   his position to be superior he may, before rolling the dice on his
   turn, double, demanding that the game be played for twice the current
   stakes. The doubling cube is then placed with the 2 side face up to
   show that the game's value has been doubled. His opponent must either
   accept the new stakes or resign the game immediately. Thereafter the
   right to redouble belongs exclusively to the player who last accepted a
   double. When this occurs, the cube is placed with the face of the next
   power of two showing.

   The game is rarely redoubled beyond four times the original stake, but
   there is no theoretical limit on the number of doubles. Although 64 is
   the highest number depicted on the doubling cube, the stakes may rise
   to 128, 256, 512 and so on.

   In money games, a player is often permitted to beaver when offered a
   double, doubling the value of the game again, while retaining
   possession of the cube.

   The Jacoby rule allows gammons and backgammons to count for their
   respective double and triple values only if there has been at least one
   use of the doubling cube in the game. This encourages a player with a
   large lead in a game to double, possibly ending the game, rather than
   to play the game to its conclusion in hopes of a gammon or backgammon.
   The Jacoby Rule is widely used in money play but is not used in match
   play.

   The Crawford rule is designed to make match play more equitable for the
   player in the lead. If a player is one point away from winning a match,
   his opponent has no incentive not to double; whether the game is worth
   one point or two, the outcome of the match is unaffected. To balance
   the situation, the Crawford rule requires that when a player first
   reaches a score one point short of winning the match, neither player
   may use the doubling cube for the following game, called the Crawford
   game. After the Crawford game, normal use of the doubling cube resumes.
   The Crawford rule is used in most match play.

   Sometimes automatic doubles are used, meaning that any ties in the very
   first roll of the game automatically double the stakes. Thus, after a
   3-3 roll, followed by a re-roll of 5-5, followed by a re-roll of 1-4 to
   begin the game itself, the game would be played for quadruple stakes.
   The doubling remains in the middle, with both players having access to
   it, and the Jacoby Rule is still in effect. Again, automatic doubles
   are common in money games. but they are rarely, if ever, used in match
   play.

Variants

   There are many variants to standard backgammon rules. Some are played
   primarily throughout one geographic region, and others add new tactical
   elements to the game, such as by altering the starting position,
   restricting certain moves, or assigning special value to certain dice
   rolls.

Acey-deucey

   Acey-deucey is a variant of backgammon in which players start with no
   checkers on the board, and must bear them on at the beginning of the
   game. The roll of 1-2 is given special consideration, allowing the
   player to select doubles of her choice. A player also receives an extra
   turn after the roll of 1-2 or of doubles.

Hypergammon

   Hypergammon is a variant of backgammon in which players have only three
   checkers on the board, starting with one each on the 24-, 23- and
   22-points. The game has been strongly solved, meaning that exact
   equities are available for all 32 million positions possible in the
   game.

Nackgammon

   Nackgammon is a variant devised by Nack Ballard. It differs only in its
   initial setup: each player starts with two checkers on the 24-point,
   two checkers on the 23-point, three checkers on the 8-point, and four
   checkers each on the 13-point and 6-point. Each side still has fifteen
   checkers total, but with two checkers on each side starting further
   back, there is more initial contact between the two sides, and less
   chance the game will quickly develop into a race.

Old English

   Old English backgammon restricts the number of checkers to a maximum of
   five on each point, thus forbidding some moves that might otherwise be
   made. A player may also opt to play one part of a roll in such a way
   that the rest may not be played.

Strategy

   Backgammon has an established opening theory, although it is less
   detailed than that of games like chess. The tree of checker positions
   expands quickly because of the number of possible dice rolls and the
   moves available on each turn. Recent computer analysis has offered more
   insight on opening moves, but the midgame is reached quickly. After the
   opening moves, backgammon players frequently rely on some established
   general strategies, and will combine and switch among them to adapt to
   changing conditions as a game unfolds.

   The most direct and sometimes the most successful strategy is simply to
   avoid being hit, trapped, or getting into mutually blocked stand-offs.
   The running game describes a strategy of moving as quickly as possible
   around the board, and is most successful when a player is already ahead
   in the race.

   A holding game is a strategy wherein a player keeps a point high in his
   opponent's board or on his opponent's bar point, as the game
   progresses. The player may gain an advantage by hitting an opponent's
   blot from the held point, or by rolling large doubles that allow the
   player to advance both checkers and begin a running game.

   The priming game involves building a wall of checkers, called a prime,
   ideally covering six consecutive points. This obstructs opposing
   checkers that are behind the blockade. The prime is usually built
   somewhere between the 11-point and the 2-point, and then shuffled into
   the home board as the game progresses.

   A blitz describes a strategy of closing the home board as quickly as
   possible while keeping one's opponent on the bar. Because the opponent
   has difficulty re-entering from the bar or escaping, a player can
   quickly gain a running advantage and win the game..

   A backgame is a strategy of placing two or more anchors (points with
   two or more checkers) in one's opponent's home board, while building a
   prime in one's own home board. The anchors obstruct the opponent's
   checkers, and create opportunities to hit them as they move toward the
   home board. The backgame is generally used only to salvage a game
   wherein a player is already significantly behind; using a backgame as
   an initial strategy is usually unsuccessful.

   Duplication refers to the placement of checkers in such a way that
   advantageous dice rolls for one's opponent are the same for a number of
   desirable moves. For example, a player may position all of her blots in
   such a way that her opponent must roll a 2 in order to hit one,
   reducing the probability that any blot will be hit. Diversification
   refers to a complementary tactic of placing one's own checkers in such
   a way that more numbers are useful.

Social and competitive play

   Medieval players, from the 13th century Carmina Burana
   Enlarge
   Medieval players, from the 13th century Carmina Burana

Club and tournament play

   Enthusiasts have formed clubs for social play of backgammon. Local
   clubs may hold informal gatherings, with members meeting at cafés and
   bars in the evening to play and converse. A few clubs offer additional
   services, maintaining their own facilities or offering computer
   analysis of troublesome plays. Some club leaders have noticed a recent
   growth of interest in backgammon, and attribute it to the game's
   popularity on the internet.

   A backgammon chouette permits three or more players to participate in a
   single game, often for money. One player competes against a team of all
   the other participants, and positions rotate after each game. Chouette
   play often permits the use of multiple doubling cubes.

   Backgammon clubs may also organize tournaments. Large club tournaments
   sometimes draw competitors from other regions, with final matches
   viewed by hundreds of spectators. The top players at regional
   tournaments often compete in major national and international
   championships. Winners at top tournaments may receive prizes of tens of
   thousands of dollars. One sponsor announced a purse of US$1,000,000 for
   a tournament held in the Bahamas in 2006.

World Backgammon Championship

   Prior to 1979, there was no single world championship competition in
   backgammon. A number of tournaments were held in Las Vegas and the
   Bahamas. Since 1979, the World Backgammon Championship in Monte Carlo
   has been widely acknowledged as the top international tournament. The
   tournament in Monte Carlo draws thousands of players and spectators,
   and is played over the course of a week.

Gambling

   When backgammon is played for money, the most common arrangement is to
   assign a monetary value to each game, and to play to a certain score,
   or until either player chooses to stop. The stakes are raised by
   gammons, backgammons, and use of the doubling cube. Backgammon is
   sometimes available in casinos. As with most gambling games, successful
   play requires a combination of both luck and skill, as a single dice
   roll can, in some circumstances, significantly change the outcome of
   the game.

Software

Play and analysis

   A screen shot of GNU Backgammon, showing an evaluation and rollout of
   possible moves.
   Enlarge
   A screen shot of GNU Backgammon, showing an evaluation and rollout of
   possible moves.

   Backgammon has been studied considerably by computer scientists. Neural
   networks and other approaches have offered significant advances to
   software both for gameplay and analysis.

   The first strong computer opponent was BKG 9.8. It was written by Hans
   Berliner in the late 1970s on a DEC PDP-10 as an experiment in
   evaluating board positions. Early versions of BKG played badly even
   against poor players, but Berliner noticed that its critical mistakes
   were always at phase changes. He applied principles of fuzzy logic to
   smooth out the transition between phases, and by July 1979, BKG 9.8 was
   strong enough to play against the ruling world champion Luigi Villa. It
   won the match, 7-1, becoming the first computer program to defeat a
   world champion in any game. Berliner states that the victory was
   largely a matter of luck, as the computer received more favorable dice
   rolls.

   In the late 1980s, creators of backgammon software began to have more
   success with an approach based on neural networks. TD-Gammon, developed
   by Gerald Tesauro of IBM, was the first of these programs to play near
   the expert level. Its neural network was trained using temporal
   difference learning applied to data generated from self-play. According
   to assessments by Bill Robertie and Kit Woolsey, TD-Gammon plays at or
   above the level of the top human players in the world.

   This line of research has resulted in two modern commercial programs,
   Jellyfish and Snowie, as well as the shareware BGBlitz implemented in
   Java, and the free software GNU Backgammon. They also offer tools for
   analyzing games and offering detailed comparisons of individual moves.
   It is worth noting that without their associated "weights" tables,
   which represent hours or even months of tedious neural net training,
   these programs play no better than a human novice.

Internet play

   Backgammon software has been developed not only to play and analyze
   games, but also to facilitate play between humans from different parts
   of the world over the internet. Dice rolls are provided by random or
   pseudorandom number generators. Real-time on-line play began with the
   First Internet Backgammon Server on July 19, 1992. The server is the
   longest running non-commercial backgammon server and enjoys a strong
   international community of backgammon players. Several commercial
   websites also offer on-line real-time backgammon play. Yahoo! Games has
   offered a Java-based online backgammon game since 1997. MSN Games
   currently offers a backgammon game based on ActiveX. The online
   gambling industry began to expand its offerings to include backgammon
   in 2006.

   Retrieved from " http://en.wikipedia.org/wiki/Backgammon"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
