Arimaa/Glossary

Adjacent

The d4 square is adjacent to c4, e4, d3, and d5. In Arimaa, adjacent does not include diagonals, which have no place in the rules.

Arimaa Challenge

First held in 2004, the Arimaa Challenge was an annual match between a top bot and top human players. Humans dominated for eleven years, until a bot's surprise victory in 2015.

Away trap

An opponent's home trap: c6 and f6 are away traps for Gold, while c3 and f3 are away traps for Silver.

Basket

A basket is like a frame or fence, but does not directly involve a trap square. A piece in a basket is blocked in any direction it could move if it were unfrozen.

Blockade

A blockaded or smothered piece is surrounded by pieces which it can't push away. A blockaded square is occupied by a piece which can't be pushed off. See also Phalanx, Frame, Immobilization.

Camel

The second strongest of the six unique Arimaa pieces. Each side has one camel.

Capture

A capture removes a piece from the board; a piece is captured when it occupies a trap square with no friendly piece beside it.

Cat

The fifth strongest of the six unique Arimaa pieces. Each side has two cats.

Choke

A choked piece is blocked by its own rabbit. Unable to retreat homeward, advanced rabbits can sometimes be used against their owner.

Dislodge

To push or pull an opponent's piece. Dislodge should not be confused with capture.

Dog

The fourth strongest of the six unique Arimaa pieces. Each side has two dogs.

Draw

Prior to July 1, 2008, one who had lost all eight rabbits could still get a draw by capturing all remaining enemy rabbits. Draws are no longer possible, as a game now ends when one side is out of rabbits.

East wing

The right side of the board viewed from Gold's perspective, specifically the f-, g-, and h-files.

Elephant

The strongest of the six unique Arimaa pieces. Each side has one elephant, which is the only piece that cannot be pushed or pulled by the opponent.

Elephant deadlock

The two elephants are deadlocked when both remain next to the same trap, preventing any capture therein.

Elimination

A player wins by elimination if the opponent has no rabbits left. In the rare event that each player loses his last rabbit in the same move, the one who made the move wins. See also Goal, Immobilization.

Endgame

The game phase when a goal line can no longer be blocked reliably, and thus gameplay centers around goal threats. See also Opening, Middlegame.

Exchange

An exchange or trade occurs when each side captures material within a few turns. If each side captures a rabbit, that is a rabbit exchange. If the gold camel is captured and then a silver horse is captured, that is a camel-for-horse exchange. See also Sacrifice.

False protection

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.

Fence

A fenced piece is stuck next to a trap, and could only step into that trap. A fence may result in a capture, frame, or hostage.

File

One of eight columns on an Arimaa board. From Gold's perspective, the a-file is on the left and the h-file is on the right. From Silver's perspective, it is the reverse.

Flip

In one turn, a piece might pull and then push a weaker enemy piece; the stronger piece finishes where it started, having flipped the enemy piece two squares. A piece surrounded on three sides cannot do a flip, as there is not room for the movement.

Fork

A forked 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.

Four-for-two

A four-step move which can be undone in two steps by the opponent. Like three-for-ones, four-for-twos usually give away time.

Frame

A piece which is on a trap square, securely surrounded on three sides by opposing pieces, has been framed. Its lone friendly defender is pinned. See also Basket, Phalanx, Blockade.

Freeze

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 until the stronger enemy piece leaves. A frozen piece can still be pushed or pulled by the opponent.

Free piece

A free piece can move around with limited risk. Blockades, frames, hostages, trap attacks, and goal threats may restrict pieces on both sides, leaving other pieces to decide the game. Having the strongest free piece or strongest local piece can be a large advantage.

Friendly piece

For Gold, any gold piece is a friendly piece. For Silver, any silver piece is friendly. Friendly pieces can unfreeze each other or protect each other from capture.

Goal

If a rabbit reaches the opponent's home rank, the game is won by goal, which is the usual way a game ends. See also Elimination, Immobilization.

Goal attack

An ongoing goal threat. See also Trap attack.

Gold

Gold is the player with gold pieces. Gold is both the first to set up and the first to move. See also Silver.

Hang

A hanging piece is exposed to immediate or forced capture. See also False protection.

Home trap

A trap on a player's third rank. The squares c3 and f3 are Gold's home traps; the squares c6 and f6 are Silver's home traps. See also Away trap.

Horse

The third strongest of the six unique Arimaa pieces. Each side has two horses.

Hostage

A hostage piece is held near a trap and threatened with capture should a friendly defender leave.

Immobilization

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 Freeze, Blockade, Goal, Elimination.

Key square

A square north, south, east, or west of a trap square. See also Trap attack.

Lemming

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.

Linchpin

A stabilising piece in front of a friendly piece which might otherwise be vulnerable. If the gold camel is on b3 and intends to stay there, Gold might have a linchpin horse on a4 to prevent his camel from being frozen on b4 in the event it is pulled up.

Middlegame

The period between the opening and endgame.

Mutual protection

When two or more friendly pieces protect each other from capture in a trap they are adjacent to. See also False protection.

Opening

The period from setup roughly until the first capture. See also Middlegame, Endgame.

Overload

Multiple threats might overload the enemy elephant, if no other piece can defend.

Phalanx

When every square a piece could be pushed onto is already occupied. A phalanx may be part of a larger blockade, or may simply block a particular move.

Pin

A lone friendly piece supporting a framed piece is said to be pinned. If a pinned piece moves, the framed piece disappears instantly.

Pinch

A capture defense in which an enemy piece is surrounded so that it cannot pull or flip a piece into a trap.

Postal game

A game in which players have at least a day to complete each move, allowing for deeper exploration than would a live game.

Pull

A piece can pull a weaker enemy piece by first stepping onto an unoccupied adjacent square, and then moving the enemy piece onto the square that was just vacated. A pull uses two steps.

Pull and replace

When a piece pulls a weaker enemy piece, and then a friendly piece steps onto the square the enemy piece was pulled from.

Push

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 uses two steps. A phalanx may block a push.

Push and replace

When one piece pushes another and steps away, allowing a different friendly piece to take a square formerly occupied by an enemy piece. See also Pull and replace.

Quadrant

A 64-square board can be divided into four quadrants of 16 squares each. In Arimaa, each quadrant contains one trap.

Rabbit

The weakest unit on the board, and the only piece that cannot be moved backward by its owner. Each player starts with eight rabbits, and aims to eventually get one to goal.

Rank

One of eight rows on an Arimaa board. Gold's home rank is 1, while Silver's is 8. The opponent's home rank is the goal line.

Repetition rule

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.

Rotation

When a piece holding a blockade or frame is replaced by a weaker piece or a phalanx, the original piece has rotated out. If a hostage defender is replaced, usually by multiple weaker pieces, the original defender has rotated out. A piece can likewise rotate out of a trap control fight. See also Swarm.

Sacrifice

A strong piece might be sacrificed so that a friendly rabbit can reach goal. A weak piece might be sacrificed while one secures a frame or hostage. Likewise, one might have to give up a piece to break an elephant blockade or stop an enemy goal.

Scatter

If there is no good way to defend against a trap attack, home pieces might scatter to avoid or delay capture.

Setup

At the start of a game, Gold sets up his pieces on the first and second ranks, in any configuration he chooses. Silver then sets up her pieces on the seventh and eighth ranks.

Silver

Silver is the player with silver pieces. Silver is second to set up and second to move. See also Gold.

Step

A piece can step onto any unoccupied adjacent square. A player takes one to four steps on any turn. Any piece move uses one step; a push or pull uses two steps, since two different pieces move.

Strength

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.

Strong piece

The elephants, camels, and horses are sometimes known as strong pieces. When one side loses two such pieces, an opposing dog might then be considered a strong piece, as it faces threats from only two enemy pieces.

Swarm

When several pieces advance toward an away trap. A swarm may allow an advanced elephant to rotate out of a trap control fight, or out of hostage defense. See also Trap attack.

Three-for-one

Three steps which can be undone in a single step by the opponent. Such a move will give away time, unless the opponent can't easily spare that one step.

Three-for-three

Three steps which could be undone in three steps by the opponent. When three steps cancel three steps, both sides have effectively taken one-step turns. This may continue for several turns, as long as the fourth steps sometimes create unique positions.

Trap

There are four trap squares on the board, located at c3, c6, f3 and f6. A piece can be captured in a trap square.

Trap attack

A trap attack entails an attempt to occupy multiple key squares of an away trap, perhaps creating capture or goal threats.

Turn

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.

West wing

The left side of the board viewed from Gold's perspective, specifically the a-, b-, and c-files.