The Arimaa challenge was won in 2015, when the bot Sharp won matches against three top human players.
The second strongest of the six unique Arimaa pieces.
A piece is captured and removed from the board if it occupies a trap square while there is no friendly piece on any of the four adjacent squares. A piece can occupy a trap square only if there is a friendly piece next to it, although an opponent might dislodge that piece and thereby capture the piece in the trap.
The fifth strongest of the six unique Arimaa pieces.
When a player's own Rabbit is used against them to help blockade a major piece. This is done by trapping the Rabbit next to the major piece, so that neither has anywhere to go. A piece's own friendly rabbit can be quite an effective blockader, since it can't step backward, and a piece can't push a friendly piece. A piece blocked by its own rabbit is said to be choked.
The fourth strongest of the six unique Arimaa pieces.
The right side of the board viewed from Gold's perspective, specifically the f-, g-, and h-files.
The strongest of the six unique Arimaa pieces. The Elephant is the only piece that cannot be pushed or pulled by the enemy.
A player wins the game by elimination if the opposing player has no Rabbits left.
Occurs when each side captures a piece of equal strength, usually within a short period of time. For example, if each side captured a Rabbit on consecutive moves it is described as a Rabbit Exchange. See also Capture.
When two friendly pieces next to a trap could each be dislodged in two steps, resulting in a capture in an apparently protected trap. See also Mutual Protection.
The combination of pulling and pushing an opponent's weaker piece such that the weaker piece appears to be flipped to a different side of the stronger piece. Weaker pieces are vulnerable to being flipped to the opponent's side and eventually captured. Two special cases are sometimes called Swing and Throw.
A fork occurs if a piece is simultaneously threatened with capture in two different traps. This can only occur on the squares c4, c5, d3, d6, e3, e6, f4 and f5.
A four-step move making a change to the position which can be undone in two steps by the opponent. Four-for-twos are seldom good moves.
A piece is frozen if it is adjacent to a stronger enemy piece and is not adjacent to any friendly piece. A frozen piece cannot move until the enemy piece moves away or a friendly piece moves onto an adjacent square.
If a rabbit reaches the opponent's home rank, the game is won by goal, which is the usual way a game ends.
The player with the Gold pieces is both the first to set up and the first to move. See also Silver.
The third strongest of the six unique Arimaa pieces.
A player wins by immobilization if the opponent has no piece which can move, or if any move the opponent could make would recreate a position they created twice before. See also Blockade
A square north, south, east, or west of a trap square.
When a bot sacrifices a series of pieces to protect a stronger piece from capture. Some bots don't recognize that a strong piece is doomed, and send over a weak piece to defend it, only to have the weak piece captured with nothing to show for it. The cycle may repeat several times, with the bot sending over weak pieces and the opponent capturing them.
A formation usually at the edge of the board where two friendly pieces are diagonal to one another such that if either is pulled one step it remains unfrozen due to the other friendly piece and can easily return to its original place.
A lone friendly piece that is supporting a framed piece is said to be pinned. See also Frame.
When every square a piece could be pushed onto is already occupied; if the opponent can't change this, even their elephant will be blocked.
A slow game in which the players are allowed a specified number of days (sometimes hours) to complete each move. Historically postal games (e.g. chess, go) were played by old-fashioned mail and a single game could last for years. Nowadays, postal games are normally played online in a period of weeks or months. Also known as a correspondence game.
A piece can pull a weaker enemy piece by first stepping to an unoccupied adjacent square, and then moving the enemy piece into the square that was just vacated. A pull requires two steps. See also Step.
Pull and replace
A turn where a strong piece pulls an enemy piece, and then a friendly piece steps onto the square the enemy piece was pulled from.
A piece can push a weaker enemy piece by first moving it to an adjacent empty square, and then itself stepping onto the square which that enemy piece had occupied. A push requires two steps. See also Step.
Push and replace
A somewhat less common variant of pull and replace.
A quarter of the board (16 squares), usually distinguished either by the trap square it contains, or by compass directions from the perspective of Gold. Thus the c6-quadrant is also the northwest quadrant, etc.
The weakest unit on the board and the only piece that cannot move backwards. However, Rabbits are extremely important due to their ability to win the game by goal. See also Goal.
One of eight rows on an Arimaa board. Gold begins the game with 16 pieces on the first and second ranks while Silver beings with 16 pieces on the seventh and eighth ranks. The home rank for Gold is 1, while Silver's is 8.
A player who has created the same position twice may never create that exact position again. This is a consideration in sequences where players undo each other's moves.
When a piece involved with holding a blockade or frame is replaced by another (usually weaker) friendly piece, the original piece is said to have been rotated out. Also, if a piece defending a hostage is replaced, usually by two weaker pieces, the original defender is said to have been rotated out.
If a player allows a friendly piece to be captured in order to pursue a strategic objective elsewhere on the board, the friendly piece is said to be sacrificed.
When a player's home trap is invaded, and nearby pieces move away to avoid being captured. See also Invade.
The player with the Silver pieces is second to set up the pieces and second to move. See also Gold.
There are six unique types of pieces, each with a different strength. Stronger units can push, pull and freeze any weaker enemy pieces. From strongest to weakest, the units are Elephant, Camel, Horse, Dog, Cat, Rabbit. See also Freeze, Pull, Push.
Three steps making a change to the position which can be undone in one step by the opponent. Three-for-ones are usually not good moves.
Three steps which can be undone in three steps by the opponent. If this happens, both players are effectively making one-step moves, since the other three steps cancel each other out. This may continue for several turns, as long as the fourth steps sometimes create unique positions.
There are four trap squares on the board, located at c3, c6, f3 and f6. A piece can be captured in a trap square.
A player completes a turn by moving pieces a total of one, two, three or four legal steps. The opposing player then makes his/her turn. Also known as a move. See also Step.
The left side of the board viewed from Gold's perspective, specifically the a-, b-, and c-files.