Arimaa/Attacking/Techniques

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With camels on opposite wings, each side will likely advance on its camel wing. In a typical EMH (elephant-camel-horse) attack, the elephant advances in the center, the horse advances on a flank, and the camel advances behind the horse. The first objective is to clear a decentralized key square of the enemy trap, so that a friendly piece can occupy that square.

An early hostage would change the game plan. If an attacking piece is taken hostage by the enemy elephant, and the attacking elephant defends the hostage, that is an elephant deadlock. An elephant-less attack may then occur on the other wing. If the hostage is a camel, and the hostage-holder's own camel is already on the other wing, the hostage-holder's position may be strong. This is why a horse usually advances ahead of the camel in an EMH attack; an early horse-by-elephant hostage is less of a problem, and might even play into the attacker's hands should the defender choose to take it.

Later in the game, similar attacks may use different pieces.

Course of an EMH attack[edit]

Prelude: horse to a6[edit]

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An attack on a defended trap will entail much maneuvering on both sides. Even an attacker's first objective, getting a friendly horse onto a decentralized key square, may not be straightforward; Silver can block c7 with a phalanx, and a defending silver horse can hold b6. Often, an attacking gold horse will go to a6, hoping to later get onto b6.

Likewise, an attacking silver horse may go to h3 in hopes of later getting onto g3. Anticipating such a counterattack, Gold blockaded h3 with rabbits; the silver horse can still get to h3, but must first move the h3 rabbit to h5 or g4, which would currently take five steps. Aiming to get a gold horse to b6 before a silver horse can get to g3, Gold is not worried about rabbit pulls, which would cost Silver time.

Occupy key square[edit]

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In this diagram, Gold has just played the pull-and-replace Mb4ns hb6s Ha6e, getting his horse onto b6. Note that the a5 rabbit allowed the camel to return from b5 even with the silver elephant on c5. It is common for a weak piece to advance on the a-file, and for weak pieces to occupy c3 and two adjacent squares, to give the gold camel greater mobility with the silver elephant nearby.

The gold camel now threatens to pull the silver horse south and take it hostage, giving Gold strong threats in both western traps, which Silver must not allow. In the game, the silver horse retreated to a6, from where it might get back onto b6 with a pull-and-replace.

The silver elephant will sometimes occupy b5 to block the gold camel, if the c6 trap doesn't need the silver elephant as a direct defender. In that case, Gold could still continue the attack, but might do better to move his camel east and create a second threat.

See #Maneuvers for more examples of ways to get a key square.

Rotate out elephant[edit]

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Once one has achieved shared control of an away trap, an ideal continuation is to replace the friendly elephant with a weaker piece. From this position, Silver played 11s De3e ed3e dd4s cf6e, now defending c3 with a camel and dog, and thus freeing the silver elephant to deal with Gold's attack at f6. The gold elephant, by contrast, must stay by c3 to prevent material loss, so the elephant rotation gives Silver the strongest free piece for now. In other cases, the removal of the attacking elephant might also free the defending elephant, but the lasting shared control should still give the attacker an advantage.

The right piece to replace the elephant depends on the defenders in the vicinity. In this case, no gold horse was near d3, so a silver dog could do the job. The presence of the gold dog on d2 might have allowed Gold to reclaim d3 with a pull-and-replace (12g Ec4ew dd3n Dd2n), but here that fails to 12s ee3n Dd3e dd4s dd5s, after which the silver dog on d4 blocks the pull-and-replace.

Alternative: switch wings with the camel[edit]

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In this game, the gold camel helped the gold horse get onto g6, and the camel now hastens west to defend against Silver's threats there. Gold is ahead, but his position is not ideal, as he has no good way to free his elephant. Meanwhile, the silver blockade on g7 stops the gold horse from penetrating further into Silver's camp. Without that blockade, Gold might have moved the horse to f7 and controlled g6 with his camel. Instead, Gold will have to find a slower way to use his trap control advantage.

Some noteworthy features of the position:

  • The g5 rabbit stops Silver from regaining g6 with a pull and replace. This defensive pull and replace is a common idea, as is blocking it by occupying g5.
  • Silver must keep a piece on d6 to stop Gold from flipping the f6 horse. If Gold could remove the silver horse from the northeast, the silver army would be unbalanced, and a gold dog could become a strong eastern attacker. Such a flip occurred on 12g in this game, giving Gold strong trap control.
  • If Gold has time to advance the h2 rabbit to h6, Silver will be cramped in the east.

Defences[edit]

Counterattack[edit]

While not strictly a defense, a counterattack is often the correct response to an EMH attack if the defender's camel is on the other wing. Such positions are extremely sharp, and a difference of a few steps can be crucial. In an opening with camels on opposite wings, it is typically an advantage to have greater development on one's camel wing. Also, if the elephants are on the same wing this tends to favour the side whose camel is not on that wing, since that camel is the strongest piece on its wing.

Bring the camel[edit]

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Silver brings the camel (game)

When an attacking horse occupies a key square, the defending camel might move through the back ranks to take it hostage. This is in some ways an ideal response to an attacking horse, but is not always feasible. The attacker might pull a back-rank rabbit into the path of the defending camel. Since it couldn't retreat, that rabbit might have to advance further, perhaps maneuvering around pieces, to get out of its friendly camel's way. The attacking elephant itself might sometimes go to the seventh rank to block the defending camel.

Even if the camel can get to the attacking horse, the attacking elephant may be a problem for the camel; while the camel came west, the attacker may have been maneuvering to make a horse-by-camel hostage harder to maintain. Furthermore, the attacking side might retreat the horse a square or two while preparing an attack on the other wing, intending to slowly advance whichever attack the defender is less able to respond to.

More generally, strong defenders are often needed to stop an attack. In this game Gold won material using his camel, then moved it through the back ranks to blunt Silver's eastern attack, since it no longer had large targets in the west.

Stuff the trap[edit]

The defender might blockade squares around the trap to deny the attacker room to maneuver. In addition, it can be valuable for either side to occupy the trap square itself. If one side occupies the trap, the other cannot readily move pieces through the trap. The piece on the trap might move off to defend the trap if necessary. If one might be forced to quickly abandon the trap, but still wants to occupy it, the weakest piece possible should be used.

Rabbit blockade[edit]

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Gold's own rabbits block his northeastern attack. (game)

In the game at right, Gold advanced a rabbit to h5 in order to make g5 mobile for his camel, which he intended to use for a pull-and-replace that would get the h6 gold horse onto g6. Silver foiled this plan by pulling another gold rabbit to g5. Since rabbits can't retreat, the g5 and h5 rabbits and thus also the h6 horse are stuck in place as long as the adjacent silver pieces stay put. While the gold elephant stays by the trap, Silver should keep these rabbits in place; framing one would break this blockade, which stops any Gold attack on the east wing. If the gold elephant leaves e6, the blockaded h6 horse may then be vulnerable to the silver camel, and of course the gold rabbits can be captured when Silver chooses.

A flank rabbit advance may aid an attack, but the attacker should take care not to let a second rabbit get pulled up if the two rabbits together might block the attack.

Horse-by-elephant hostage[edit]

An attacking gold horse might be taken hostage by the silver elephant. This is usually a bad long-term strategy, but it is still a way to slow an attack, and might possibly result in a horse frame. It may be best for an attacking horse to initially go to a7 rather than a6, so the defending elephant can't even think about going after it.

Maneuvers[edit]

Here are some ways for an attacker to get initial shared control of an enemy trap. There is no simple recipe for attacking: any of these maneuvers might be prevented by the defender, and the rest of the board must be considered before pieces are committed to a local fight. The following are simply some common tactics that both an attacker and defender should be aware of.

The positions are all from actual games (which are linked) except that they are transferred to the c6 area, swapping colours if necessary.

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The horse dives through the trap: Hb5en cc7n Hc6n. This may be dangerous for Gold if the silver camel is at home; even if the camel can't immediately take the gold horse hostage, the silver elephant may block the horse from retreating while the silver camel comes west. To prevent such a dive, the defender can either use a c7 phalanx or stuff the trap.
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Gold to move defeats the c7 phalanx with Ed6e cd7s cc7e Hc6n. The gold piece on c5 is essential, since otherwise the horse would be lost when the elephant stepped away. Were Silver to move here, the gold horse could be framed, although there would then be a chance for a pull-and-replace to get the gold horse onto b6.
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Silver has blockaded b7 against the advancing horse, but Gold defeats the blockade with Ed7s dc7e rb7e Ha7e.
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Gold to move does a pull-and-replace (Mb4ns hb6s Ha6e), taking shared control of c6 while also threatening to pull the silver horse to c3. Silver could then do a pull-and-replace to frame the gold horse; the frame would not hold for long, but might buy Silver time. If Silver is to move, she might place her elephant on b5 to block the gold camel, and also counterattack in the east.
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The gold camel goes directly into b6 with the gold horse on a6. Gold plans either to retreat the camel and move the a6 horse to b6, or to move the camel through the trap to c7 or d6. Beware double hostages and blockades: in the linked game, the move (played on 22g) that created this position was a mistake, because Silver blockaded the trap square, while Gold's own rabbits stopped the gold camel from retreating.
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Gold just played Rb2nn db6e Mb5n. The a7 horse stops the camel from being taken hostage. In the game Gold was subsequently able to push the silver horse down the a-file and take a strong hostage.
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Silver has blocked the gold camel, but Gold to move can still play a pull-and-replace with Ed6we hb6e Ha6e. Silver to move can prevent this by stuffing the trap, but the piece in the trap may be vulnerable to being flipped towards c3, especially if it is a cat or rabbit.
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Gold plays Ec5we hb6s Ha6e. This one is relatively easy, but since the gold elephant is not on d6, the silver camel might come over and threaten to hostage the gold horse. The attacking elephant probably wants to move to d6 regardless, so this maneuver loses a bit of time even if the defending camel doesn't cause a problem. Note that Gold could move his elephant to b5 ahead of time, but if the silver elephant could then reach c5, that would ruin Gold's plan and marginalize the gold elephant.
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The gold camel has just moved to c6, threatening to reach c7 or help the gold horse onto b6. If the silver elephant goes south and then east, the silver horse might be pushed towards c3. Camel-in-trap can be played with the gold elephant on c5 or d6; the a6 horse makes a camel hostage unlikely. The camel is however vulnerable to a fork between c6 and f6; Silver can now play hb6n eb5n Mc6e eb6e, though the camel could then escape. If the silver elephant were more centralized, it might pull the camel out for a fork; an attacker with a piece in the trap must watch for this, if the attacking elephant is not on d6.
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From this position the gold elephant occupied b6, pushing the defending horse away; the c4 gold horse then took b6 in what amounted to a multi-turn push-and-replace. A free silver camel could have punished the gold elephant's decentralization, but in this case the camels were deadlocked on the other wing.