Arimaa/Setup

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There are 64,864,800 possible setups for each side, although Gold in effect only has half that many, since an east-west reflection amounts to the same setup for the one going first. Players frequently experiment with different setups, but certain guiding principles are usually followed:

  • Elephant centralisation: The elephant usually starts on the d- or e-file; less commonly, on the c- or f-file.
  • Activity: A piece typically does not start directly behind a weaker piece. For example, the elephant should always start in the front row, as should the camel unless it starts directly behind the elephant.
  • Defence: It should be possible to defend the key squares b3 and g3 (or b6 and g6) in the opening. Often, the initial setups will see b2, g2, b7, and g7 each occupied by a camel or horse.
  • Balance: Whether or not a setup is totally symmetric, there should be some strength on each wing, so that neither home trap can be attacked too easily.
  • Rabbit protection: Since rabbits can't retreat, they should not begin exposed to easy pulls.

A small minority of the possible setups obey these rules. However, there is still plenty of scope for variation. Unusual setups, especially those which place rabbits in front of strong pieces, may be a form of handicap.

In the opening, the elephants tend to stay in the centre, while camels and horses often choose a wing. Therefore, the most basic characteristic of a setup is the placement of the camel and horses. A symmetric setup, with the camel in the centre and a horse on each wing, is the most flexible. However, some prefer to begin with the camel decentralized; the enemy elephant could block the camel's movement no matter where the camel was, so it might be best to immediately commit the camel to one wing, and thus force the enemy elephant to decentralize itself if it wants to fight the camel. Asymmetric setups are more common with Silver than with Gold; if the gold camel began decentralized, the silver horses could both start far away from it, giving Silver an early alignment advantage.

Symmetric setups[edit]

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The diagram shows two standard symmetric setups. Gold uses the most common gold setup since 2005, known as the classic 99of9. A 99of9 setup places the elephant and camel on d2 and e2, the horses on b2 and g2, and the dogs and cats on d1, e1, c2, and f2. Rabbits are arranged so that they won't get in the way of friendly pieces; a rabbit advanced in the middle could be a problem, whereas the opponent has less to gain by pulling an a- or h-file rabbit. Eventually, the c- and f-file rabbits might step into the center to block the goal line.

Cats often start behind the traps, but a dog behind a trap would make that trap safer from attack, since a dog can't be pushed aside by an enemy dog. Cats and dogs are therefore sometimes swapped in the 99of9 setup. However, the d- and e-file pieces will affect the center, so "cats behind the traps, dogs back" is more common than the reverse. Moreover, the piece behind a trap will most likely be the first to go if the opponent takes over the trap, so it makes sense to have that piece be small.

Silver's setup, known as the Fritzlein setup, puts rabbits behind the traps, leaving the cats slightly more active since they may at some point advance along the b- and g-files. The downside is that, in the event of a trap control fight in silver territory, the c7 or f7 rabbit could be pulled into the trap and then could never step back, making things awkward for Silver.

Note that the silver elephant does not directly face its gold counterpart. Had Silver placed her elephant on e7, the gold elephant could immediately go to e6 and delay the silver elephant's advance. That would be bad for Silver, but only because of her symmetric setup, which allows Gold to advance his elephant without fear of a quick attack that could compel the elephant to return home.

MH setups[edit]

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At left, Silver uses an asymmetric setup popularised by browni. Silver plans to move her elephant to d3 or c4, move her western horse to a3, and use her camel against the western gold horse, so that Silver can occupy b3. Key to Gold's response is his camel, which could move west for defence, or east for a camel-horse counterattack against f6; the gold camel should quickly commit to one or the other, before Silver gets an advantage.

Silver's attacking threat justifies having her elephant directly face the gold elephant. Gold might play 2g Ed2nnnn, but then Silver could play 2s ha7s mb7s cc7w hg7s and 3s ed7wsse. Silver has lost some time with sideways steps, but Gold will lose even more time moving his elephant, which will have to step around its silver counterpart and go back home to defend c3.

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The setup from this game

At right, Gold plays an asymmetric setup, intending to quickly attack in the west with elephant, camel, and horse. Silver should not respond with a symmetric setup, which would do little to counter Gold's western strength. Here Silver takes an eastern advantage while minimizing Gold's western advantage; the silver camel will slow down Gold's attack. If the d7 horse goes east, Gold might attack c6 with elephant, horse, and dog, while moving his camel east to face the silver horses.

Another idea for Silver (illustrated here) would be to put the elephant in the west and camel and horse in the east, reasoning that Silver will be faster in an attacking race since Silver's attack is further from the elephants. Yet another idea, from this game, is to play an approximate mirror image of Gold's setup, leading to a slow maneuvering opening.

HH setups[edit]

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The setup from this game

At left, Silver has used an HH setup, placing both horses on the same wing. From here, the gold camel should probably move west to face them. Silver's plan is to create a strong western threat, restricting the gold elephant to defense and perhaps blocking the gold camel, making the silver camel the strongest piece in the east. Silver's HH wing threat usually involves homeward pulls, hence this setup is typically played less aggressively than MH setups. With three horses on one wing, framing tactics may come to the forefront.

The proper response by Gold is an unsettled question. If the gold horse can advance in the west, this may lead to a strong attack on the c6 trap, but forcing the horse past the silver horses can be tricky. Alternatively, Gold might attack the f6 trap, which will be highly vulnerable if the silver camel can't hold a key square.

As with MH setups, HH setups are less popular for Gold. If both gold horses start on the same wing, Silver can gain time by setting up with the camel already facing them. Silver might also avoid having a horse directly face the gold camel.

Statistics[edit]

Percentage popularity of camel and horse distributions for Gold
Silver responses to a symmetric gold setup
Average number of forward rabbits

These statistics are based on games between two humans rated over 1800. Setups where one wing has no horse or camel are rare and excluded here. Note that in this classification, 'old-style' EHH setups (e.g. with b- and d-file horses) are counted as central horse setups.