03 What are the basic rules of the game? (Backgammon)

Backgammon Equipment
* A Backgammon board or layout.
* Thirty round stones, or checkers, 15 each of two different colors,
generally referred to as `men'.
* A pair of regular dice, numbered from 1 to 6. (For convenience,
two pairs of dice, one for each player, are generally used.)
* A dice cup, used to shake and cast the dice. (Again, it is more
convenient to have two dice cups.)
* A doubling cube---A six-faced die, marked with the numerals
2,4,8,16,32 & 64. This is used to keep track of the number of
units at stake in each game, as well as to mark the player who
last doubled.

The backgammon board

Backgammon is an obstacle race between two armies of 15 men each,
moving around a track divided into 24 dagger-like divisions known as
``points''.

The Backgammon layout is divided down the center by a partition, known
as the ``bar'' (See Diagram 1), into an outer and inner (or home)
board or table. The side nearest you is your outer and home tables;
the side farther away is your opponents outer and home boards. The
arrows indicate the direction of play.

For purposes of convenience we have numbered the points in the
diagram. Though the points are not numbered on the actual board, they
are frequently referred to during play to describe a move or a
position. Your (X's) 4-point or 8-point will always be on your side of
the board; your opponent's (O's) will always be on his side of the
board.

A move from your 9-point to your 5-point is four spaces (the bar does
not count as a space). A move from White's 12-point to your 12-point,
though it crosses from his board to yours, is but one space, for these
two points are really next to each other.

Diagram 2 shows the board set up ready for play. Each side has five
men on his 6-point, three men on his 8-point, five men on his
opponent's 12-point, and two men, known as ``runners'', on his
opponents' 1-point. The runners will have to travel the full length of
the track, the other men have shorter distances to go. Note that play
proceeds in opposite directions, so that the men can be set up in two
ways. Turn the diagram upside down to see the layout if play were
proceeding in the other direction.

```      +-------------------------------------------------->
|
|   +-----------------------------< X moves this direction
|   |
|   |
|   |    13 14 15 16 17 18       19 20 21 22 23 24
|   |   +------------------------------------------+
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   |                  |   |                   |  +----+
^   v   |   Outer Board    |BAR|     Home Board    |  | 64 |
|   |   |                  |   |                   |  +----+
|   |   | P  O  I  N  T  S |   |  .  .  .  .  .  . | Doubling
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |   Cube
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   | .  .  .  .  .  . |   |  .  .  .  .  .  . |
|   |   +------------------------------------------+
|   |    12 11 10  9  8  7        6  5  4  3  2  1
|   |
|   +---------------------------------------------->
|
+---------------------------------< Y moves this direction
```

Diagram 1 (Numbered from X's point of view)

```       13 14 15 16 17 18       19 20 21 22 23 24
+------------------------------------------+
| X  .  .  .  O  . |   |  O  .  .  .  .  X |
| X           O    |   |  O              X |
| X           O    |   |  O                |
| X                |   |  O                |
| X                |   |  O                |  +----+
|                  |BAR|                   |  | 64 |
| O                |   |  X                |  +----+
| O                |   |  X                |
| O           X    |   |  X                |
| O           X    |   |  X              O |
| O  .  .  .  X  . |   |  X  .  .  .  .  O |
+------------------------------------------+
12 11 10  9  8  7        6  5  4  3  2  1
```

Diagram #2 (Numbered from X's point of view)

Object of the game

The object of Backgammon is for each player to bring all his men into
his home board, and then to bear them off the board. The first player
to get all his men off the board is the winner.

Starting the game

Each player casts one die. The player with the higher number makes the
first move, using the two numbers cast by his die and his opponent's.
In the event that both players roll the same number, it is a standoff
and each rolls another die to determine the first move. In the event
of subsequent ties, this process is repeated until the dice turn up
different numbers. (In some games, players double the unit stake
automatically every time they cast the same number; others limit the
automatic doubles to one. In tournament play, there is no such thing
as an automatic double.)

Each player's turn consists of the roll of two dice. He then moves one
or more men in accordance with the numbers cast. Assume he rolls 4-2.
He may move one man six spaces, or one man four spaces and another man
two spaces. Bear in mind that, when moving a single man for the total
shown by the two dice, you are actually making two moves with the one
man---each move according to the number shown on one of the dice.

Doublets

If the same number appears on both dice, for example, 2-2 or 3-3
(known as doublets), the caster is entitled to four moves instead of
two. Thus, if he rolls 3-3, he can move up to four men, but each move
must consist of three spaces.

The players throw and play alternately throughout the game, except in
the case where a player cannot make a legal move and therefore
forfeits his turn.

Making points

A player makes a point by positioning two or more of his men on it. He
then ``owns'' that point, and his opponent can neither come to rest on
that point nor touch down on it when taking the combined total of his
dice with one man.

Prime

A player who has made six consecutive points has completed a prime. An
opposing man trapped behind a prime cannot move past, for it cannot be
moved more than six spaces at a time---the largest number on a die.

Blots

A single man on a point is called a blot. If you move a man onto an
opponent's blot, or touch down on it in the process of moving the
combined total of your cast, the blot is hit, removed from the board
and placed on the bar.

A man that has been hit must re-enter in the opposing home table. A
player may not make any move until such time as he has brought the man
on the bar back into play. Re-entry is made on a point equivalent to
the number of one of the dice cast, providing that point is not owned
by the opponent.

Closed board

A Player who has made all six points in his home board is said to have
a closed board. If the opponent has any men on the bar, he will not be
able to re-enter it since there is no vacant point in his adversary;s
home board. Therefore, he forfeits his rolls, and continues to do so
until such time as the player has to open up a point in his home
board, thus providing a point of rentry. It should be noted, the he
doesn't loses his turn, as he still retains the ability to double his
opponent before any of his opponents rolls, assuming the cube is
centered or on his side.

Compulsory move

A player is compelled to take his complete move if there is any way
for him to do so. If he can take either of the numbers but not both,
he must take the higher number if possible, the lower if not.

[Another way of saying this...]
* If both parts of the roll can be played legally, then this must be
done. Note that you may play the roll in such a way as to move
fewer pips than the larger die indicates by playing the smaller
die first --- this is common in bearoff situations, and legal as
long as each part of the roll is played legally at the moment you
play it.
* If only one part of the roll can be played legally, then you must
play the higher die if possible; if not, play the lower die.

--kw

Bearing off

Once a player has brought all his men into his home board, he can
commence bearing off. Men borne off the board are not re-entered into
play. The player who bears off all his men first is the winner. A
player may not bear off men while he has a man on the bar, or outside
his home board. Thus if, in the process of bearing off, a player
leaves a blot and it is hit by his opponent, he must first re-enter
the man in his opponents home board, and bring it round the board into
his own home board before he can continue the bearing off process.

In bearing off, you remove men from the points corresponding to the
numbers on the dice cast. However, you are not compelled to remove a
man. You may, if you can, move a man inside your home board a number
of spaces equivalent to the number of a die.

If you roll a number higher than the highest point on which you have a
man, you may apply that number to your highest occupied point. Thus,
if you roll 6-3 and your 6-point has already been cleared but you have
men on your 5-point, you may use your 6 to remove a man from your
5-point.

In some cases it may be advantagous to play the smaller die first
before applying the higher die to your highest point (See Compulsory
Move). For example, suppose you have one checker on your 5 point, and
two checkers on your 2 point. Your opponent has a checker on the ace
(one point) and on the bar. You roll 6-3. You may play the 3 to the 2
point then the 6 to bear a checker off the 2 point leaving your
opponent no shots (no blots for the opponent to hit). The alternative,
using the 6-3 to bear checkers off both the 5 and 2 points, would
leave your opponent 20 out of 36 ways to hit your remaining blot.

Gammon and Backgammon

If you bear off all 15 of your men before your opponent has borne off
a single man, you win a gammon, or double game.

If you bear off all 15 of your men before your opponent has borne off
a single man, and he still has one or more men in your home board or
on the bar, you win a backgammon, or a triple game.

Cocked dice

It is customary to cast your dice in your right-hand board. Both dice
must come to rest completely flat in that board. If one die crosses
the bar into the other table, or jumps off the board, or does not come
to rest flat, or ends up resting on one of the men, the dice are
``cocked'' and the whole throw, using both dice, must be retaken.

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