The Arimaa Challenge was won in 2015, when the bot Sharp won matches against three top human players.
An opponent's home trap: c6 and f6 are away traps for Gold, while c3 and f3 are away traps for Silver.
A basket is like a frame, but not on a trap square. A piece in a basket is blocked on three sides, and can't escape on the fourth side.
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. There are two ways a piece might be captured: it could be dislodged into an undefended trap, or might already be on a defended trap square which then becomes undefended.
The fifth strongest of the six unique Arimaa pieces.
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 by elimination if the opponent has no rabbits left.
An exchange occurs when each side captures material within a few turns. If a gold rabbit is captured and then a silver rabbit is captured, this is a rabbit exchange. If the gold camel is captured and then a silver horse is captured, this is a camel-for-horse exchange. Also called a trade.
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.
In one turn, a piece can pull and then push a weaker enemy piece, so that the stronger piece finishes where it started, and the weaker piece has in effect been flipped. Any non-elephant piece could potentially be flipped into enemy territory, and perhaps forked.
A fork occurs when one piece is simultaneously threatened with capture in two different traps. The forked piece would have to be on c4, c5, d3, d6, e3, e6, f4, or f5.
A four-step move which can be undone in two steps by the opponent. Like three-for-ones, four-for-twos are seldom good moves.
A piece is frozen if no friendly piece occupies an adjacent square, and a stronger enemy piece does occupy one. A frozen piece cannot move until a friendly piece is beside it, or the stronger enemy piece leaves.
Gold is the player with gold pieces. Gold 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 hostage piece is held near a trap and threatened with capture should a friendly defender leave.
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.
Not recognizing a lost cause, some bots will go all out to save a doomed strong piece. The bot sends over a weak piece to defend it, only to have the weak piece captured with the strong piece no better off. The cycle may repeat several times, with the bot sending over lemmings and the opponent capturing them.
An elephant is said to be overloaded if its side faces multiple threats which no other piece can defend against. Any piece might get overloaded, which could require a stronger piece to be used inefficiently, which could ultimately lead to an elephant overload.
A lone friendly piece supporting a framed piece is said to be pinned.
A defence in which an enemy piece is surrounded so that it has no room for a flip.
A slow game in which the players are allowed a specified number of hours or days 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 over 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.
Pull and replace
A turn where a piece pulls a weaker 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.
Push and replace
A quarter of the board (16 squares), distinguished by compass directions from the perspective of Gold. The northwest quadrant contains the c6 trap, the northeast contains f6, the southwest contains c3, and the southeast contains f3.
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.
One of eight rows on an Arimaa board. Gold begins the game with 16 pieces on the first and second ranks, while Silver begins 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 holding a blockade or frame is replaced by a weaker piece or a phalanx, the original piece has been rotated out. If a hostage defender is replaced, usually by multiple weaker pieces, the original defender has been rotated out. A piece can likewise be rotated out of a trap control fight.
When a player's home trap is invaded, nearby pieces may scatter to avoid being captured.
Silver is the player with silver pieces. Silver is second to set up and second to move. See also Gold.
There are six unique types of pieces, each with a different strength. A piece can push, pull, or freeze any weaker enemy piece. From strongest to weakest, the units are elephant, camel, horse, dog, cat, and rabbit.
When several weak pieces advance toward an away trap. The aim may be to replace the defender of a hostage, blockade a strong enemy piece, threaten goal, or just strengthen one's forces around that trap.
Three steps that could be completely undone in one step by the opponent. It is usually wasteful to take three steps which can be canceled with one, since that would effectively lose two steps.
Three steps which can be undone in three steps by the opponent. If this happens, both players have effectively taken one-step turns, 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 gets a turn. Also known as a move.
The left side of the board viewed from Gold's perspective, specifically the a-, b-, and c-files.