2005 Challenge Match
Bomb faced stiffer competition in the 2005 Arimaa Computer Championship than it had the previous year, and advanced to the challenge match only on tiebreaks. David Fotland had improved Bomb mostly by fixing small bugs and fine-tuning the evaluation function, but he also added one important strategic innovation: Bomb became selectively aggressive with its camel when the two elephants were tied up in a hostage situation.
Human understanding of Arimaa had expanded considerably in the intervening year, in particular with initial exploration of the elephant-horse attack. Despite these advances, some suspense crept back into the Challenge when the two top-rated human players declined to participate based on time commitments. Omar Syed (then ranked #3) did not want to defend his own prize again, so he persuaded Frank Heinemann, the only other human player rated higher than Bomb, to do the honors.
Heinemann entered the match rated a mere 55 points higher than Bomb, a gap that would imply only a 58% chance of winning each game. The superficially close match eventually turned into a rout, though, as Heinemann launched the elephant-horse attack in game after game, and perfected his technique as the match progressed. In the first game Bomb never got much going with its camel counter-attack, and in the second game it was too little too late. Heinemann engineered an elephant smother to dominate the third game.
In the fourth game, Heinemann attempted another elephant smother, which Bomb sidestepped at the last moment to enter an unclear midgame. Without any guiding strategic theme (no camel hostage, no blockade, no EH attack) Heinemann faltered and lost a double-edged endgame. That was to be Bomb's only victory. In the fifth game Heinemann caught Bomb's counter-attacking camel in exchange for a horse, and in the final three games, Heinemann won without losing a piece.
The final score of 7-1 in favor of Heinemann showcased his human adaptability, as his elephant-horse attack improved and Bomb's response remained static.
