Backgammon

Backgammon is a traditional Saxon game opposing two players. There exist a lot of ancestors everywhere around the world and they are probably coming from antic Roma or even earlier.
The objective is to take all your tokens out of the board, before your opponent do the same. One play with a pair of classic six-faced dice and with a specific board composed of 24 squares.

Game rules

The board

The backgammon board is composed of 24 squares, divided into 4 quadrants of 6 squares each, or, otherwise seen, two lines of 12 squares.
Squares are numbered clockwise, starting at 1 on the bottom right, 12 on bottom left, 13 on top left, and 24 on top right.
Another way to describe it is to say that the track forms an horse iron open on the right.
Tokens of the first player will go through the board from square 24 to square 1, while those of the second player will go in the other direction, from square 1 to 24.

Normally, the two right quadrants are called interior quadrants, and the two on the left the exterior quadrants. As well, each one's camp is the above or below part containing their starting square (on top for the first player, containing square 24, and the bottom for the second player, containing square 1).
Finally, the bar separate the two camps.

Each player initially owns 15 tokens, placed as follows: 2 tokens on square 24, 3 tokens on square 8 and 5 tokens on squares 13 and 6 for the first player, and symetrically, 2 tokens on square 1, 3 tokens on square 17 and 5 tokens on squares 12 and 19 for the second player.

Movements

At each turn, dice are rolled and one or two tokens are advanced of the number of squares indicated by the dice.

One can move twice the same token in a row, as long as each move is run in a clearly distinguishable way one after the other. Thus, for example, if you rolled 3 and 6, you can't advance a token directly by 9 squares; but you can advance it first by 3 squares and then by 6, or the opposite, first by 6 squares and then by 3, depending on your choice and your possibilities.
One can of course also advance a token by 3 squares and then another by 6 or conversely. The order in which dice are played is indifferent.

Well distinguish moves one from another is very important because everything isn't allowed (see further below). IN the previous example, it may be the case that the token you want to move could advance by 9 squares directly, but couldn't neither advance by 3 nor 6 squares, in which case you can't touch that token this turn.
You will have to play another token if you can. It could happen sometimes that you are forced to skip your turn or a part of it because no moves are possible.

When rolling double, dice are played twice instead of just once. Thus, for example, by rolling 5 5, you can run four moves of 5 squares each instead of just two.
In such a case, you can move four times the same token, or four different tokens, at your choice.

Barriers and captures

When moving a token, you can make it arrive on a free square, or on a square where there are already one or more of your tokens.

You can also move a token on a square occupied by a single token of your opponent, in which case it is captured. A captured token is placed in the bar and must re-enter the board before any other movement
You can't move any token on the board as long as you still have one or more of your tokens captured by your opponent on the bar.
A 1 on a die allow to make a token re-enter on square 1 or 24, a 2 on square 2 or 23, etc. of course in your camp, squares 19 to 24 for the first player and squares 1 to 6 for the second player.

You aren't allowed to place a token on a square already occupied by two or more tokens owned by your opponent; the later are forming a barrier.
It is therefore impossible for a square to have tokens of both players at the same time.

Exiting tokens

When all your tokens have been brought to your interior quadrant, respectively in squares 1 to 6 and 19 to 24, the exit phase can start.
A 1 on the die allow to exit a token from square 1 or 24, a 2 on the die from square 2 or 23, etc.

If there is no token in the exact required square, you can make tokens exit the board from more advanced squares, but only if there is no token in previous squares.
For example with a 4 on the die, you can always exit a token from square 4; you can also exit a token from squares 3, 2 or 1, but only if none of your tokens are on squares 4, 5 or 6.
In this case, this implies that all dice points may not be used completely. Such unused dice points are lost.

IF one of your tokens is captured during your exit phase, you are no longer allowed to make tokens exit the board until the captured token hasn't re-entered the board and reached again the last interior quadrant.

Winning, gammon and backgammon

To win the round, you must exit all your tokens from the board. So a victory point is counted. A complete game is usually played in 3, 5 or 7 points, which are reached in several rounds (at least 3).
Given that the randomness of the dice take an important part in the game, it is rather unusual and unappropriate to finish a complete game in a single round.

If you manage to make all your tokens exit the board while your opponent didn't take any, two victory points are counted instead of just one. This is called gammon.
If you finish while your opponent still has tokens on the bar or in his first interior quadrant, whether he already exited tokens or not, this gives a backgammon which is worth three victory points.

Doubling die

At any time, you are allowed to request a doubling of the stack. IF your opponent accepts, the game continue; if he refuses, then he immediately loses the round.
By doing it, the round will be worth two victory points instead of just one, and therefore the value of a gammon goes to 4 points and a backgammon to 6.

Once you doubled the stack and that your opponent accepted, he has then the hand on the doubling die. This means that he's now the only one allowed to make a new doubling request.
IF he makes a new request and if you accept, the round will be worth quadruple and you again take the hand back on the doubling die. In case you would like to request a third doubling, the value of the round could come to 8 points, and so on.
IN theory, there is no limit in the number of doubling that can be requested, but having a round worth 16 points ore more is quite rare.

Given that one can't refuse a doubling request made by the opponent, you aren't allowed to request it in any situation. For example in a game in 7 points, if your opponent is winning 6-5, you aren't allowed to request a doubling. Normally, in this situation, you would need a gammon, or two simple wins, in order to win the whole game. Doublign would remove that obligation and would allow you to win the game in a single simple win. Otherwise said, this would superficially remove the advantage your opponent had against you in the score.
More generally, as soon as doubling would allow to win immediately the game or remove such score advantages, it isn't allowed.

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