Arimaa/Trap Control

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Silver's long-term threat to c3 is strong.


Trap control is related to ownership. A trap might be fully controlled by one side, or might be shared. At the outset, each player essentially has full control of his two home traps. Trap control depends on the key squares, especially the decentralized ones (e.g. b6 and c7 in the northwest, b3 and c2 in the southwest). Getting a non-elephant safely onto a decentralized key square of an away trap is an important step toward wresting control of that trap. Even if one doesn't take full control of an away trap, strong shared control can impact the rest of the board.

In this opening, a horse procured a long-term trap control advantage for Silver. Although Silver had no immediate way to force a capture, Gold had no direct way to deal with the intruding silver horse: the silver elephant would stop the gold camel, and Gold could not afford to decentralize his elephant just to deal with a horse. From here, Silver swarmed the c3 trap and overloaded Gold, whose elephant stayed beside c3 and thus could not defend in the east.

Deadlocked TrapsEdit

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There is an elephant deadlock at f6 and a camel deadlock at c3. (Game)

A trap is deadlocked when its strongest gold defender and strongest silver defender are equal. In the event of an elephant deadlock, no capture will be possible in the deadlocked trap until an elephant chooses to leave. If both elephants stay beside the same trap, it is usually because both sides have a large stake there. Remember that a hostage position can tie down both sides, as a hostage could become an attacker if the hostage-holder simply left. Here, the silver elephant is not holding a hostage, but is defending against an attack which more gold pieces might soon join.

A camel deadlock will hold only so long as neither elephant can be bothered to break it. Despite Silver's material advantage, she has more to lose than does Gold, as a threat to the silver camel would by extension threaten the horse which it defends. If Silver were to now abandon f6 and attack c3, Gold would easily win the race, as the gold camel would have to be removed from b3 before any capture could occur in c3. When there are two deadlocks, the side with the advanced elephant may have potential for a quick cleanup in either trap. Gold could move his horse to f7, advance more pieces in the east, and rotate out his elephant. If he does not feel confident about that strategy, he might retreat his horse and immediately move his elephant toward c3.

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Gold will lose a horse for abandoning c6; Silver will lose a dog and some rabbits for abandoning c6.

Since no capture is possible in a trap defended by both elephants, the player whose home trap is deadlocked is often at a space disadvantage, especially if his elephant is decentralized. Enemy pieces can safely advance toward such a deadlock, whereas the home elephant would have to leave if it wanted to ensure safe advances of its own pieces. If the deadlock is the result of a hostage position, the defender's space advantage might allow him to rotate his elephant out of hostage defense.

Before and after diagrams illustrate the effect of gold rabbit advances on a northwestern elephant deadlock. In the before diagram, Gold would stand to lose his horse if his elephant abandoned c6. If the silver elephant abandoned c6, the gold horse and elephant together could force the capture of any silver piece near the trap. This is typical of an elephant deadlock: it would be costly for either elephant to leave.

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Gold will lose a horse and some rabbits for abandoning c6; Silver will lose a dog, some rabbits, and the game for abandoning c6.

In the after diagram, gold rabbit advances have further raised the stakes for both sides. If the gold elephant abandoned c6, Silver would then clean house. If the silver elephant abandoned c6, a gold rabbit would soon reach goal. With so much now at stake in the northwest, the deadlock has tightened considerably.

Having effectively committed to the c6 trap, Gold should now advance his western dog and then his camel, so that his elephant can rotate out before the silver camel does much damage in the east. Had Gold kept his western rabbits at home, he could have moved his camel to the g- or h-file to pull silver pieces toward f3. The difference would be that Gold could more easily afford to abandon c6 if that only meant giving up a horse, especially if he captured the silver camel in return. Moreover, Gold's goal line would be well-defended had the gold rabbits stayed at home, so there would be less risk of a quick goal attack by Silver.

One whose elephant is stuck in a home deadlock must ensure that the enemy elephant has no good way to leave. One unprepared to make a strong second threat should avoid getting into a home elephant deadlock; for example, taking a hostage could backfire if one is not already poised to attack on the other wing.

Stronger vs. weaker piecesEdit

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At each trap, the strongest local piece faces multiple weaker pieces which protect each other.


Shared trap control also occurs when one side has the strongest local piece, but the other has multiple weaker pieces which protect one another from capture. After 23s of this game, all four traps were contested in such a manner. A capture will be possible only when one side can establish full control of some trap. When a strong piece moves from one fight to another, the area it leaves could become vulnerable; here, Gold would face at least a horse loss in f6 if he moved his elephant. A position with multiple trap control fights may amount to a race, as things will move quickly if each side prioritizes offense.

Losing controlEdit

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As long as Gold owns no trap, Silver has nothing to fear. (Game)

Silver currently defends all four traps, and will face no capture threat until Gold can change that. The gold elephant can't take a strong hostage, and can't afford to leave c3. Even if one can take a seemingly strong hostage, it won't ultimately be effective without a second threat. To have any chance here, Gold must advance his camel and reassert full control of f3; if that draws the silver elephant east, Gold can then own c3 instead of f3. Once Gold owns a home trap, he might then attack the away trap on that wing. It is crucial to own at least one trap, so that the opponent is somewhat limited by capture threats.


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Silver owns no traps, and can't even move pieces through her home traps.

In this game, Gold's advances gave him strong shared control of both c6 and f6. As long as the silver elephant defends f6, the gold elephant can dominate the west. Gold's home defense is now thin, though it would not be easy for Silver to get anything started.