Arimaa/Introduction to Strategy
Arimaa strategy involves straightforward concepts which overlap in complex ways. Very different styles of play remain popular; some players are quite aggressive, quickly advancing piece after piece with the aim of controlling the entire board. Others prefer to play a "home game", initially advancing only their elephant and maybe a horse. Reckless advances can be punished with basic tactics, but measured advances can be very effective if they are part of a long-term plan.
The most direct strategy in Arimaa is to try to rip a hole in the goal line and then march a rabbit through. If both players go this route, the game turns into a race; if a race begins right away, it may favor Gold since Gold goes first. Fortunately for Silver, racing is not one's only option.
Defending one's home territory is important; a player who neglects home defense will tend to lose to one who prioritizes it. Thus one should not begin the game aiming to force a goal. Instead, there will likely be several intermediate steps, although one might get an early goal if an aggressive opponent leaves a hole open.
As long as there is no real opening in the goal line, it is futile to advance a rabbit for the purpose of reaching goal. Remember that an advanced rabbit can't retreat, and thus is quite vulnerable to capture. Generally speaking, it would be extremely wasteful to use one's elephant to protect a rabbit.
In short, going for a direct goal is a poor strategy which can quickly set one back. Nevertheless, a goal path must eventually be cleared somehow.
The next obvious strategy is that of capturing pieces, though that is not straightforward either. A piece is captured only when it is on a trap square with no friendly piece beside it; an opponent has many ways to prevent a capture. If nothing else, the defending elephant can camp out by a trap where there is a capture threat; since nothing can dislodge an elephant, its friendly pieces can never be captured in a trap it stays next to.
The key to progress is to make strong threats around two different traps, overloading the enemy elephant. The elephant can only defend one trap, and any other piece which tries to prevent a capture might be captured itself.
The simplest double threat is a fork between one's home traps. If a piece can be flipped in the center, it may be doomed to such a fork. This is one of many reasons both elephants might stay near the center. Although any piece can unfreeze a friend, an elephant can do so without putting itself at risk. Since rabbits can't retreat, they are often not placed in the center.
Pieces advanced on the wings are less vulnerable to a fork. It is easier to forcibly drag down a piece right against the edge, but then it is harder to force capture if the defending elephant stands in between traps.
If both sides take care to prevent a fork, the threats will have to be more sophisticated.
|In this game, the silver camel has been taken hostage.|
In the diagram, Gold has taken the silver camel hostage, threatening to capture it in c3 if Silver does not adequately defend the trap. A solid camel hostage will make the forces asymmetrical: with the gold elephant holding the silver camel hostage and the silver elephant defending it, the gold camel is the strongest free piece. Using his camel, Gold can make a threat in the east, overloading Silver's defences. A hostage is only one way one can get the strongest free piece, which is often a large advantage.
The risk of a hostage might make one reluctant to advance any piece other than the elephant. Also, one might jump at any chance to take an enemy piece hostage. However, holding a hostage can be costly. If the elephants are deadlocked at one's home trap, that is a space disadvantage, since the opponent can safely advance pieces toward the deadlocked trap, but the home elephant is not available to ensure safe advances of its own friendly pieces. A home hostage-holder can't simply leave, as the former hostage could then team up with its elephant to force captures in the trap, which would clear space for a goal. In fact, the defending elephant often has better prospects for leaving; if its friendly pieces do advance toward the trap, they might eventually defend it without the elephant.
Given all this, one should be selective about hostage-taking. A camel-by-elephant hostage may be worthwhile, but a horse-by-elephant hostage usually isn't. While the enemy camel remains, a long-term horse hostage should only be held by one's camel; pieces should be used efficiently. A good horse-by-camel hostage forces the opposing elephant to defend, while making the hostage-holder's elephant the strongest free piece.
|In this game, Silver is making threats in c3 and c6.|
If a piece cannot be taken as a strong hostage, it can safely advance. In the opening, for instance, the most reliable advances (other than of the elephant) are of horses on the wing away from the enemy camel. In the game shown, the silver horses were able to advance with impunity because the gold camel was far away.
The main use of advanced pieces is to take control of an away trap. They can also drag enemy pieces back to the home trap. Here Silver has taken control of c3 and pulled out the gold dog as a hostage, and Gold cannot defend both. Away trap control has various advantages besides material gain, such as the possibility of starting a goal attack. If a silver rabbit can advance to the c3 area, it will be a strong threat to reach goal. At least while the board is fairly full, successful goal attacks usually require sharing control of an away trap.
Home and away games
If pieces cannot safely advance on a wing, the opponent might pull them in order to take a hostage. There are therefore two basic plans – advance pieces, or pull enemy pieces – which might respectively lead to positions known as home and away games. Since rabbits cannot retreat, they could in principle be pulled out gradually over several turns. Early in Arimaa's history, rabbit pulling was considered an important element of opening strategy.
However, pulling pieces cedes valuable space and time to the opponent, who might use this to develop pieces with the long-term aim of competing for trap control. Although the proper balance between attack and defence is not easy to ascertain, strategy has moved towards earlier development and aggression. Many rabbit pulls are now considered dubious.
A recurring theme in Arimaa strategy is elephant mobility. Sometimes an elephant gets blockaded, but more often it is restricted by the cost of leaving a particular trap. Before getting into a position that will require one's elephant to stay put, one must consider the opposing elephant's situation. If one elephant is even slightly more free than the other, this can snowball, since it affects how free other pieces are.