Arimaa really is interesting

The computer is stymied by making the growth in possible positions per ply MUCH faster than in chess: first, because each player arranges his pieces as he wants at the start of the game—and in a neat bit of komi, Gold must arrange his pieces first, so Silver gets to see Gold’s arrangement before he (Silver) arranges his own pieces—an advantage—but Gold gets first move—also an advantage; and second, because on each ply (i.e., on each player’s turn), he gets 4 “moves” as we would normally say—moving 1 piece 4 squares, or 4 pieces 1 square, or any combination. So LOTS of possible positions for each ply, above and beyond all the possible opening positions.

The strength of pieces is monotonic—from strongest to weakest: Elephant > Camel > Horse > Dog > Cat > Rabbit. Interestingly, the size of the strength discrepancy between two pieces is (so far as I can tell at this point) immaterial: it’s a simply binary, stronger/weaker relationship, without any consideration of the degree of strength difference.

The move rules are simple: all pieces move exactly the same, which is one square orthogonally in any direction, save that rabbits (the weakest and most numerous piece, played by chess pawns) cannot move backward voluntarily. No diagonal moves, and diagonals (in effect) don’t count.

And no capturing, but the stronger of two pieces can push or pull the other—a notion that I think kids would understand from their own experience.

So it’s an up-close game, but since you can move as many as 4 pieces a turn, I would think it would have a broad strategy. What’s cool in the links below is that you can listen as one of the players goes over a world championship game. I don’t know the combinations he names, as yet, but still it’s possible to follow the general discussion, and I find it fascinating.

The instructional videos are succinct and informative. This whole list is from one page of the incredibly resource rich Arimaa site.

• Arimaa Tutorial (Flash version) – 500 KB
  • Watch this animation to learn the rules in just a few minutes.
• Arimaa Tutorial 2 (Flash version) – 1 MB
  • Aamir teaches Arimaa.
• 2009 World Championship Final Game
  • Video of Jean Daligault commenting on a championship game against Karl Juhnke.
• 2008 Postal Tournamnt Game
  • Video of Karl Juhnke commenting on a postal game against Ned Bent.