Arimaa/Other Hostages
As with a camel hostage, a horse or smaller piece hostage will be effective only if it gives the hostage-holder a usable advantage in free pieces.
Horse-by-elephant hostages
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Gold's camel is more free than Silver's. |
Even with camel hostages, the hostage-holder is often more stuck than the defender, since the hostage could become an attacker if freed. This gets worse if an elephant holds a horse hostage instead, as occurred in this opening. If the silver elephant left the northeast trap, the gold horse would likely help its elephant make captures, perhaps decimating Silver's eastern forces. Thus both elephants are basically stuck, but consider the overall position. Gold would gladly trade his horse for the silver camel, which if it came east might get forked between c3 and f3. The gold camel is much less restricted, as it would face no such fork threat even if the silver elephant were to abandon the northeast trap. The camels are the strongest free pieces, but Gold's camel is more free, thus the hostage does not benefit Silver. Ultimately, this is an issue of alignment; decentralizing one's elephant on account of an enemy horse is highly questionable.
For now, the gold elephant is better placed on e6 than on f5. If e6 and e7 were clear, the silver elephant could pull the gold horse onto e7 and then fork it between traps. That is a possible advantage of positioning a hostage-holder behind the trap.
In some cases, a horse-by-elephant hostage might be converted to a frame or passed off to the silver camel. If Silver were better positioned for that, it would be urgent for Gold to prevent a solid frame or horse-by-camel hostage, which could free the silver elephant while the gold elephant remained stuck defending the horse.
Gold can begin to advance in the east, but should try to avoid having a second piece taken hostage while the gold elephant is still needed for defense. The more Gold has at stake in the northeast, the more aggressive Silver can afford to be elsewhere.
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The dogs are the strongest free pieces. |
A horse-by-elephant hostage may be effective on a depleted board. In this endgame, such a hostage tied up the three strongest remaining pieces. Up two-to-one in dogs, Silver can dominate the rest of the board. If a second gold horse or dog remained, this hostage would likely be weak.
Horse-by-camel hostages
The camel is usually the piece that should fight an enemy horse long term. This may lead to a horse-by-camel hostage, which will ideally tie the opposing elephant to defense while the hostage-holder's elephant is free to roam. However, the "defending" elephant can often attack the hostage-holding camel, and thus turn the tables. If the hostage is defended by the enemy elephant, a hostage-holding camel will need friendly support. If a solid horse-by-camel hostage is feasible, it may be worth using considerable material on, since it can give one the only free elephant.
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These diagrams illustrate different horse-by-camel hostage configurations, with Gold holding such a hostage in the southwest. A gold piece is always on a4, to keep the gold camel mobile if it is pulled to b4. In the first diagram, note that the b2 cat allows capture of the hostage if the silver elephant goes to b4. Gold should leave d3 clear, so that the camel could finish on d3 after making that capture. The b2 cat and empty d3 square indirectly protect Gold on the b-file; if the silver elephant could afford to step west and begin the next turn on b4, things could quickly turn around. As things stand, this may be a solid hostage position for Gold, whose own elephant is the strongest free piece for the time being.
Without a gold piece securely on a4, the hostage would be weak. With ec4we Mb3n ha3e, Silver could have her elephant on c4 and her horse on b3; if the gold camel were frozen on b4, Silver would have strong capture threats in c3, and could also flip the gold camel to c5 with a threat to capture it in c6. The a4 square is thus crucial to such a hostage position, and Gold does well to have a horse on that square, as a weaker piece could be pulled away more easily.
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In the second diagram, the hostage horse is on b2 rather than a3; this has implications if the camel is dislodged. For instance, if the silver elephant moved to b4, it would then threaten to capture the camel due to false protection. On the other hand, Gold now has the option of pushing the horse to b1. If the silver elephant left, the horse could then be pulled back to b2.
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In the third diagram, the silver elephant cannot easily displace the gold camel. As long as Gold can hold b3, Silver could break this hostage position only by decentralizing her elephant. A horse hostage behind the trap can be quite strong, if there are enough pieces to support the camel while its elephant is active elsewhere.
In all of these cases, the defender should consider bringing in more pieces if possible. In the last example, Silver might have a strong position if she could bring a horse to b3, dislodging the gold dog. In the first, the silver camel might attack the a4 horse, weakening the hostage pattern.
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Gold cannot save both horses. |
While a horse-by-elephant hostage is usually a bad long-term strategy, it may be an effective tactic if the hostage-holder can make a quick second threat. In this opening, Silver took both gold horses hostage, and Gold did not have time to defend both traps.
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To break this hostage, the gold elephant would have to go to f7. |
When a hostage-holding camel is behind a trap, the defender might be no better off if he pushes the camel away. On 13g of this game, Gold played Ce1n Ee6n mf7s Ee7e; Silver moved the d6 rabbit to e6, and Gold had no active strong piece. When the gold elephant left f7, the silver camel retook the hostage. It is sometimes possible to free such a hostage, but that could be slow, and the enemy elephant could dominate in the meantime. Furthermore, the hostage piece and defending elephant might both get blockaded in the corner.
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Silver's horse-by-camel hostage allows silver dogs to control an away trap. |
By tying up the gold elephant and horse while other strong pieces were tied up in the west, Silver's horse-by-camel hostage at right enabled silver dogs to control f3. This led to a 29-turn win.
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Gold holds a camel hostage in the east, and a double hostage in the center. |
In this game, Gold's central horse-by-camel hostage stopped Silver from forcing a western goal; with the d2 horse frozen and other silver pieces blocked out of the southwest, there was nothing to help the silver elephant counter Gold's defense. This would be a strong position for Silver if he could displace the gold camel, but Gold to move can blockade c3 and perhaps move toward a northwestern goal threat. With the southern forces tying each other down, the western gold horse is the strongest free piece; the silver elephant must stay beside c3, and cannot freeze the gold horse in place. One way or another, this horse can soon accomplish something.
Cat and dog hostages
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Silver does not have an ideal alignment, but may eventually overload Gold. (Game) |
A smaller piece may also make a valuable hostage, if its elephant is the only piece which can defend it. In this example, the silver camel holds a gold dog hostage next to c6. The silver elephant is free to pull gold pieces toward f6. The gold elephant can't defend both traps.
However, Silver's situation is less than ideal, for two reasons. First, the gold elephant could currently leave the c6 trap without losing the c8 dog on the next turn, since the silver cat would have to leave the trap square to allow for the capture. Second, the h5 gold rabbit will make it harder for the silver elephant to threaten the gold camel. Silver might have to capture the h5 rabbit before making any other threat in f6.
Silver would have a greater advantage if her horse held the dog hostage and her camel were free; with the gold elephant stuck defending against a silver horse, the silver elephant and camel together could make a strong threat elsewhere. Like a horse-by-elephant hostage, a dog-by-camel hostage is at best non-ideal in most situations.
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Gold's dog-by-horse hostage allowed the gold camel to safely advance to g6. |
In this game, Gold's early dog-by-horse hostage allowed for an elephant-camel attack on f6. An early camel advance would often result in a camel hostage, but the southeastern hostage gave Gold time to advance his camel and support it with rabbits.