Game: Arimaa
Invented and implemented by Omar and Aamir Syed, November 2002
See the 'Learn to Play' section on
www.arimaa.com for an animated tutorial.
Arimaa was designed to be difficult for computers to play, yet easy for people to learn and play. A challenge of $10,000 USD is offered to the first person or company that can build a computer program which can defeat the best Arimaa player prior to 2020.
Objective
The first player to get just one Rabbit across the board to the other side wins. If both players lose all their Rabbits the game is a draw.
Setup
The game has no fixed starting position for the pieces. The game starts with an empty board. First Gold sets down all the pieces in any order on the first 2 rows. Silver can then set down all the pieces on the first 2 rows closest to Silvers side. Once the peices have been set down the players take turn moving the pieces with Gold going first. Each player has 8 Rabbits, 2 Cats, 2 Dogs, 2 Horses, 1 Camel and 1 Elephant.
Steps
In each turn the players can take up to 4 steps. All pieces move the same way, which is laterally (i.e. left, right, forward and back). Except that Rabbits cannot move backwards. Moving a piece from its current square to an adjacent square counts as one step. The 4 steps can be distributed across multiple pieces. Thus a player can move one piece 4 steps, four pieces 1 step each,one piece 3 steps and another piece 1 step, etc. The same piece may take steps in different directions. At least 1 step must be taken on each turn to change the state of the board.
Pushing and Pulling
A piece can push opponents weaker pieces to any laterally adjacent square and move into its place. This is called 'pushing' and uses up 2 steps; one for pushing the opponents piece and one for moving into its square. Pushing must be completed within a players turn and cannot be distributed across turns. The Elephant is the strongest and can push any other piece except another Elephant. The Elephant is followed in strength by the Camel, then the Horse, Dog, Cat and finally the Rabbit which is the weakest and cannot push any other piece. Pieces of equal strength cannot push each other.
A piece can also pull opponents weaker pieces which are laterally adjacent into the square that it moved from. This is called 'pulling' and uses up 2 steps; one for moving the piece and one for pulling the opponents piece. A piece cannot pull while completing a push.
Freezing
A piece that is alone and laterally adjacent to an opponents stronger piece is considered 'frozen' and cannot move. A piece is considered to be alone if there is no friendly pieces laterally adjacent to it. The lonely weaker piece can be 'unfrozen' by moving any other friendly piece next to it. When no longer alone the weaker piece is unfrozen and can immediately begin to move within the same turn.
Traps
The squares c3, f3, c6 and f6 are called 'traps'. Any piece that is standing on a trap square is immeadiatly removed from the board if there are no friendly piece laterally adjacent to it.
A piece may safely stand on or pass through a trap square as long as there is a friendly piece adjacent to it. If the friendly piece moves away then the lonely piece on the trap square is immeadiately removed from the board.
The development of Arimaa began on January 15th 1999 while Omar Syed was trying to teach his son Aamir how to play Chess. By the way the name Arimaa is really A followed by Aamir spelled backwards.
Updated 05/10/03
several modifications by L. Lynn Smith
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