2007 World Championship

From ArimaaWiki

It's that time of year again, when we gear up for the annual tournament to decide who will be Arimaa World Champion. Last year a record 16 players from six countries participated. This year 20 players from ten countries have registered, easily setting another record. Arimaa continues to expand in popularity, despite a complete lack of advertising. Unfortunately, the top players from Japan, Singapore, and China did not register. Each of the three has a high rating and a legitimate chance to win, so it is a shame that Asia is not better represented. The tournament format will be floating double-elimination. Everyone plays one game per week until losing twice. Last one standing is Champion!

Fritzlein is the top seed based on rating, despite finishing tied for fourth last year. Robinson, the reigning World Champion, is the third seed this year, behind 99of9, who won the annual postal tournament 10-0 while robinson went a disappointing 4-6. On the other hand, 99of9 has played only a handful of live games in the past six months, so he may be rusty. Chessandgo, the fourth seed, has practiced more than anyone in the past month, and looks to be a threat to win it all despite only learning to play Arimaa eight months ago. Equally impressive is the twelfth seed Brendan, who learned the rules just two months ago and is still rising in rating game by game.

Contents 1 Round 1 2 Round 2 3 Round 3 4 Round 4 5 Round 5 6 Round 6 7 Round 7 8 Round 8 9 Second Place Game

Round 1

The first round was marred by two forfeits. Brendan's Internet connection at his new flat was not installed Friday as hoped, so he forfeited to jdb. OLTI missed a train home from a weekend trip, so seanick benefited with a forfeit win. Also connection troubles decided two other games, with naveed losing on time to arimaa_master from a favorable opening, and megamau losing on time to Adanac in an unclear position.

The other six games of the first round were won by the favorites in each case. The most exciting game was omar vs. Chegorimaa, in which Chegorimaa cut omar's elephant off from the center, and captured a horse for free on move 10. However, omar fought back, accumulating hostages and frames, and by move 33 had material equality with a very favorable position. A quick goal attack gave omar the victory seven moves later.

Robinson's victory over woh and chessandgo's victory over fritzlforpresident were notable for their brutality. Each of the high seeds attacked full out and each soon framed an opposing piece in an opposing trap! Committing three heavy pieces (EHH or EMH) to an immediate attack was unheard of a year ago, but has become the hottest trend in the months leading up to this year's championship. Robinson won in twenty-five moves, while chessandgo went one better.

99of9, PMertens, and Fritzlein took longer to win over their respective opponents richard, Tore, and Idaho_Ev, but none of the favorites was ever in danger, and each sealed a victory in under 40 moves. The shift towards attacking play, whether one is ahead or behind, is neatly summarized by this statistic: Last November the seven full first-round games averaged 45 moves per game, but this November the six full first-round games averaged 33 moves per game.

The parallel prediction contest rewarded confident betting on the favorites, because all the favorites won. Ultra_Weak took a 100-point lead over Ron_Weasley in second place, while another fourteen players were within 200 points of Ron_Weasley. Given that toss-up games cause an average swing of more than 100 points between players who guess right and those who guess wrong, the leaders will have to be prescient to stay in front.

Round 2

In the first game of the second round, Brendan made woh look like a newcomer, which is notable since Brendan is also a newcomer himself. Woh valiantly postponed his loss to move 42, the first game of the tournament over 40 moves, but he never managed to pose a threat on offense.

After missing a train the first round, OLTI had no better luck in the second round, as his Internet connection from his dormitory proved too unreliable, and he ultimately timed out. The 35 moves of his game that happened first, however, were exciting. Idaho_Ev, despite 20 of 20 predictors betting against him at an average confidence of 95%, managed to get a powerful horse-frame/horse-hostage combination. OLTI had just managed to fight back and even the position materially at a horse for a dog and a rabbit when his connection went down for good.

After getting behind in rabbit-pulling, Adanac uncorked his characteristic EMRR attack against PMertens, but PMertens pulled a marvelous jiu-jitsu move, using an advanced rabbit to hem in Adanac's elephant on e3. By move nineteen, PMertens had trapped Adanac's EMHRRRRR in an unbreakable blockade. PMertens used his free elephant and camel so efficiently thereafter, his move 31 was simultaneously a goal and an immobilization.

Chegorimaa launched an immediate EH attack against fritzlforpresident, who never found an effective answer for it. Chegorimaa gradually increased the strategic bind until he was able to start winning pieces right and left. The modern aggressive style is not merely being touted by a few players, it has permeated throughout the ranks.

Arimaa_master had a great shot at knocking off the #2 seed 99of9, winning a camel for horse plus rabbit in the opening, and following up his material gain with a dangerous attack on both of 99of9's traps. 99of9 captured a stray dog in the melee, but had an untenable position which looked destined to collapse until an inaccuracy by arimaa_master on move 19 let 99of9 return the dog for a camel hostage. When 99of9 later captured the hostage camel for a horse, he was up a clear rabbit, and only increased the pressure from there, easily winning a goal race on move 35.

Robinson's EHH opening proved difficult for jdb to counter, and by move 35 robinson had collected a material advantage of DCR for nothing. But then jdb got a horse and a dog in excellent hostage position with his camel. Jdb increased the pressure until he evened the material at a net DR for H on move 58. However, a tactical miscalculation by jdb on move 62 cost him a horse and turned the tide for good.

Megamau vs Tore was the only truly defensive opening of the round, and nothing much happened until move 17 when Tore hung a dog. Another cycle of defense and slow rabbit-pulling followed until move 43 when Tore, in an attempt to save an advanced rabbit, allowed his elephant to be blockaded. Still, Tore fought hard until losing two horses for one around move 54, after which his position fell apart.

Fritzlein departed from his usual ultra-conservative style to voluntarily advance a rabbit column against seanick. Seanick defended very solidly, but never framed attacking pieces or took them hostage. Also he didn't counter-attack. Around move 27 it was finally clear Fritzlein had achieved something, and seanick needed to become more active. Seanick's bid for counter-play resulted in his camel becoming hostage, after which the rest of the game was a plodding mop-up in classic Fritzlein style.

Chessandgo attempted to blitz omar in the opening, and got a free dog before Omar managed to regroup and create complications. Just then, on Omar's 30th move, the arimaa.com server crashed. Fortunately the game was restarted and both players were able to play it out. Chessandgo gained a material advantage of HD for R, and was able to share control of both of Omar's traps for the rest of the game, until punching through a rabbit.

In the last game of the round, richard did not show up and forfeited to naveed.

The average move number in completed games this round was up to 46, much more like last year, although still only one of the games featured a defensive dual-lone-elephant opening.

In the prediction contest, Ultra_Weak held on to his lead, although PMertens jumped to within 60 points by betting 100% on himself when most others favored Adanac. Confident betting on favorites was punished by that game, by OLTI's timeout, and by megamau's upset of Tore, but the favorites swept the other six, leaving it unclear whether the risk-takers or the hedgers did better as a group. In the future it will be the good-guessers who fare well, as many remaining games will be coin flips. The competitive field thinned out somewhat: 6 players trail Ultra_Weak by 230 or less, but only 9 total are within 530.

Round 3

The first game of the third round was a stunning upset. The predictors had Idaho_Ev as 97% to lose to Adanac, an even greater underdog than he was last round, but Idaho_Ev was undaunted. He opened aggressively, and pushed a horse behind Adanac's home trap by move 10. On move 12, Adanac began a counter-attack with his camel on the diagonally opposite trap. With elephant vs. elephant on one trap and camel vs. camel on another, it wasn't clear how either player would make progress, but both pushed pieces forward rapidly. On move 17, Adanac decided to switch quadrants with his elephant, initiating a deadly race. Idaho_Ev couldn't avoid material loss, but Adanac couldn't stop Idaho_Ev's goal.

Jdb vs. seanick was the second defensive (i.e. dual-lone elephant) opening of the tournament. Eventually jdb pulled a rabbit, then took a camel hostage. When seanick gave up the camel to prevent material loss elsewhere, he was able to create counterplay for a while, but in the long run jdb's extra material was too much to overcome.

Brendan took the fight to arimaa_master's half of the board with early piece and rabbit advances. Arimaa_master framed Brendan's wayward horse, but couldn't keep it imprisoned as Brendan's rabbits and camel sailed to the rescue. By move 27 Brendan's camel had taken arimaa_master's horse hostage in exchange for a rabbit. A bit later, Brendan's elephant separated arimaa_master's camel from his other pieces. The camel hostage seemed destined to decide the game, until Brendan let it go to pursue a goal attack. In response, arimaa_master freed his horse hostage as well, and appeared to have just achieved a very good position strategically when he overlooked a goal threat on move 47.

Chegorimaa won by forfeit over naveed, which means naveed is out with one win and two losses after having played just four moves total on the board.

99of9, in his postal tournament games, had introduced the Arimaa community to the EHH attack for the first time, and he stuck with it against PMertens in their game this round. PMertens took one of 99of9's encroaching horses hostage with his camel, so 99of9 tried to complicate the situation as soon as PMertens' elephant left the vicinity. 99of9 lost cat and rabbit for only a rabbit, but managed to get his second horse involved in the attack. For a while it seemed that 99of9 was keeping his hopes alive by making one counter-threat after another, so that PMertens couldn't capture anything more. Then, on move 33, PMertens sacrificed his camel in exchange for a goal attack in the opposite corner. 99of9 had little choice but to accept the sacrifice, and PMertens slid a rabbit to goal three moves later.

Megamau vs. omar began defensively, but when omar took a cat hostage, megamau was forced to try to rescue it with an EH attack, which resulted in his horse being framed before long. When megamau sought counterplay with his camel, omar released the framed horse and eventually secured a camel hostage in exchange for a rabbit. Megamau gave up the hostage camel for a horse, then lost a rabbit for a net material disadvantage of M for H. Omar made the ending exciting by entering into a goal race rather than playing defensively, but he raced better than megamau. When megamau timed out on move 47, omar was a few moves from goal.

The climactic game of the round between chessandgo and robinson was the sort of thrill ride to be expected from two masters of attack. Chessandgo pulled a rabbit for an early advantage, but robinson advanced pieces to contest chessandgo's home traps. By the time the exposed rabbit fell, each player had initiated an elephant-horse attack, while trying to fend off the opponent's attack with little pieces. Soon a third trap became contested, and then all four were in play at once. After a cat trade, chessandgo extended his material lead to two rabbits, with no serious weaknesses. It looked like the game would turn into a rout, but robinson created a series of goal threats, seemingly out of thin air. But despite the scary appearances, chessandgo calmly defended, collected an increasing material advantage, and ultimately advanced a rabbit through robinson's thinned defense.

In the prediction contest, Ultra_Weak widened his lead to 217 points over Janzert in second place. Ultra_Weak guessed right on PMertens' upset of 99of9, and indeed on every game except Idaho_Ev's upset of Adanac, where he hedged enough that he gained ground on most of the field. Given all the coin-flip games, the field thinned out even further, leaving only six players within 600 points of the lead. Only eleven or twelve games remain, so unless Ultra_Weak falters, the only real drama will be for second and third place.

Round 4

PMertens launched an EHH attack against chessandgo in this round's first game, after having publicly disparaged the EHH attack, and after having dissected 99of9's EHH attack in the previous round. Sadly for PMertens, the results were as he himself would have predicted. Chessandgo quickly took an attacking horse hostage with his camel, and then, with PMertens' elephant tied to the defense of that trap, started to capture PMertens' little pieces around the rest of the board. What seemed to be a rout was given a breath of drama when chessandgo blundered a horse for a rabbit on move 27, but that still left him up DCCR for H, and his army of ants broke through not long after.

99of9 put an end to Idaho_Ev's string of upsets. Both sides launched a multi-piece attack early, but 99of9 broke off his attack with clever timing to emerge with a hostage dog. As he tried to stretch his advantage, he gave up a horse hostage in the diagonally opposite trap, and even offered to let Idaho_Ev capture it, and enter a sharp line. After Idaho_Ev declined the sacrifice, there were racing attacks on diagonally opposite traps, which netted 99of9 a camel and a horse for a dog. 99of9 then carefully shut down all counterplay and slowly increased his material advantage to win in 55 moves. Idaho_Ev, the tournament's bottom seed, put in four gutty performances against seeds #1, #2, #5, and #6.

The predictors couldn't make up their minds about omar vs. jdb, with 11 betting on omar while 10 bet on jdb. The game, despite a slow dual-lone-elephant opening, lived up to close expectations with many dramatic shifts. Jdb got the first rabbit pulls, and looked to be leading until omar pried loose a dog to take hostage. Some criss-cross attack and defense led to omar caputuring HDC while jdb took MRR, a very unbalanced situation which all material evaluation formulas consider nearly even. Jdb appeared to take control of the game by attacking one of omar's home traps with EH and the other with MR, but on move 36 he opted to break off his attack and defend his home with his horse, which resulted in omar framing a rabbit and taking a camel hostage. With nothing to lose, jdb again abandoned defense and launched an attack, only this time with camel and horse on the same side, so omar's elephant knew where to be. Jdb squirmed valiantly, but to avoid goal he had to eventually lose control of one of omar's home traps, then the other, suffering fatal material losses in the mean time.

Chegorimaa gave a scare to the top seed Fritzlein. Fritzlein pulled a rabbit early, and used it to blockade Chegorimaa's elephant between Fritzlein's home traps. Chegorimaa invaded at once with a horse, and when Fritzlein found no way to neutralize the horse while maintaining the blockade, his position gradually weakened. He eventually framed the blockading rabbit, giving up on the elephant blockade. Chegorimaa lost a horse in the other home trap, but then sacrificed his framed rabbit to set up extremely powerful goal and material threats. It looked grim for Fritzlein when he gave up a horse to get his elephant home on defense, but he then was able to slowly untangle and increase his material lead until breaking through.

Brendan's game against robinson caused much confusion. Omar, in order to accommodate a Tuesday game time for PMertens vs. chessandgo, had scheduled the games for Round 4 before everyone had a chance to enter their game time preferences. After everyone had a chance to enter preferences, Omar re-ran the scheduler to produce corrected times, but Brendan had already seen the first scheduled time, so he thought his game would start two hours later than it was ultimately scheduled for. It seemed unfair to forfeit Brendan on that ground. After much difficulty communicating with both players and finding a new time acceptable to both, the game was re-scheduled and the tournament was delayed two weeks.

When the game was finally played, robinson got nothing from his EHH setup, and neither side committed to anything until robinson advanced a rabbit on move 17 to protect his exposed camel. Brendan duly framed the exposed rabbit, and robinson abandoned it for minimal compensation on move 28, giving Brendan a clear lead. However, Brendan blundered his horse on the very next move, and never recovered from the material deficit. Robinson contested both Brendan's home traps for the rest of the game, and Brendan didn't regain full control of one until two moves before robinson forced goal around the other.

In the prediction contest, Ultra_Weak finally guessed wrong on a coin flip, favoring jdb over omar, but lost the minimum amount and retained a 198-point lead. With six or seven games remaining, the only players within 800 points of the lead are Ultra_Weak 3346; 99of9 3148; Janzert 3002; Fritzlein 2983; Ron_Weasley 2888; OLTI 2781.

Round 5

Robinson once again rolled out his favorite EHH opening against PMertens, but got nothing out of it while PMertens pulled and captured a rabbit. Then each side tried to drag a rabbit, but while PMertens let his rabbit be captured, robinson defended his framed rabbit with camel and horse to free up his elephant again. PMertens then managed to extract a series of positional concessions: a horse frame, a rabbit capture, releasing the horse frame for a camel holding a horse hostage, then a horse for dog trade. With a clear material and positional advantage, PMertens looked set to dominate, but robinson cleared out the position considerably by finding an opportunity to trade MH for MH. The material balance stayed the same, but on an emptier board more crazy things can happen. By move 63 robinson had engineered a favorable horse for dog trade, to leave himself down only a rabbit, but instead of taking the horse to finish the trade, robinson initiated a goal race. After Robinson's attack fizzled, he didn't have enough pieces to undertake anything, and PMertens soon forced goal with a cute elephant sacrifice.

99of9 opened against omar by sending his lone elephant around the back of one of omar's traps, a once-common strategy that is rarely seen these days. When omar declined to threaten an elephant blockade, 99of9's elephant emerged unscathed, dragging a rabbit behind it. In the next few moves omar focused on dragging pieces while 99of9 brought his pieces back to safety and dragged the exposed rabbit. Omar appeared to be simply losing the rabbit-pulling race, but then got counterplay via a favorable horse trade. After the horse trade, omar's persistent piece-dragging nearly won him a piece, but an inaccurate move 18 let 99of9 re-group. 99of9 then collected the stray rabbit, and forced a second horse trade on move 25, which left omar positionally weakened. Omar blundered a cat under pressure from 99of9's ensuing elephant-dog attack, and never regained control of that home trap. Omar tried to keep hope alive with a series of tactical threats, but 99of9's superior position allowed him to slowly collect an unstoppable material advantage.

Fritzlein used his elephant to take an early horse hostage against chessandgo. Unfortunately, chessandgo lost his Internet connection on move five, and was not able to reconnect again that night. Both players wanted to resume the game the following day, but Ron_Weasley, the tournament director, pointed out that the rules had no provision for resuming games, and on the contrary, stated clearly that no relief would be granted for games lost due to interface or connection troubles. Furthermore, it would have seemed unfair to resume this game after previous timeouts (naveed, meagamau, and OLTI) resulted in losses for the player having connection issues.

In the prediction contest, Ultra_Weak erroneously backed robinson, so his lead shrank to a mere 83 points over 99of9. The five remaining players with a shot at the money are Ultra_Weak 3477; 99of9 3394; Janzert 3284; Ron_Weasley 3277; Fritzlein 3236.

Round 6

With only four remaining players, only one possible pairing avoided repeated matchups: Fritzlein vs. PMertens and chessandgo vs. 99of9.

Fritzlein's lone elephant opening was effective against PMeterns. Fritzlein first pulled a rabbit, then took a counter-attacking horse hostage with his camel, and then captured the exposed rabbit. With a small but clear material and positional advantage, Fritzlein blundered horribly on move 21, allowing his elephant to be blockaded. There was still some fight in the position, but Fritzlein panicked while PMertens deftly advanced his forces, keeping a hammerlock on the position. Fritzlein ultimately forced a release of the elephant blockade in a clumsy fashion that caused devastating material losses, after which PMertens patiently mopped up and won in 56 moves.

The dual-lone-elephant opening in chessandgo vs. 99of9 resulted in an early horse exchange, another once-common motif that has become quite rare of late. In the resulting even position, 99of9 immediately launched an elephant-horse attack into the teeth of chessandgo's camel, giving up a horse hostage for no compensation. When 99of9 tried to complicate by advancing his camel on the opposite flank, chessandgo attacked with a dog against 99of9's exposed home trap, and freed his elephant to switch sides and threaten 99of9's exposed camel. In the ensuing complications, chessandgo captured the two hostages (horse and camel) for two dogs by move 23. At enormous material disadvantage, 99of9 had few strategic options. He launched a doomed goal race, which chessandgo won a dozen moves later.

In the prediction contest, Fritzlein's loss actually gained him a few points relative to the other four top predictors who all backed him and lost points. The system rewards slow losses, and PMertens took a long time to finish off the game. 99of9, in contrast, was hurt by his loss to chessandgo, because 99of9 lost quickly, and moreover was forced to bet on himself while the other top four predictors backed chessandgo. Second place through fifth place is now a virtual tie. Ultra_Weak's lead of 167 points looks large with only two games remaining, but any one of the four trailers could make an extreme bet on either game and close the gap in one fell swoop. Ultra_Weak 3560; Janzert 3393; Ron_Weasley 3393; 99of9 3386; Fritzlein 3368.

Round 7

Given that each of three players left had played each of the others already, it was no longer possible to avoid a repeat pairing. The actual pairing was decided based on the assignment of the bye. Fritzlein couldn't get the bye because he had received a bye already in round three. Chessandgo and PMertens were both eligible with no byes yet and identical 5-1 records, but chessandgo got the nod by virtue of a higher pre-tournament rating. Thus PMertens and Fritzlein had a rematch.

PMertens chose an amusing opening as Gold, mimicking Fritzlein's moves from the prior round until Fritzlein unconsciously deviated as Silver. This was good enough to get PMertens the early lead in rabbit-pulling, but Fritzlein complicated by trying to pull out small pieces, and by advancing a horse. When PMertens swung his camel through the center to attack Fritzlein's exposed horse, it caused a major piece reshuffling with little ultimate effect other than giving Fritzlein a rabbit pull of his own.

Although PMertens was leading the rabbit-pulling race, he was more willing to give up his own rabbit to retain elephant mobility, just as he had done against robinson two rounds before. By move 20 Fritzlein was ahead by a rabbit, although PMertens had exposed two more of Fritzlein's rabbits. Fritzlein then used the temporary protection afforded by his exposed rabbits to run his own camel through the center, attacking PMertens' exposed horse. When the situation clarified by move 30, Fritzlein was still up a rabbit, and had taken PMertens' horse hostage with his camel, but PMertens had framed one of Fritzlein's rabbits in each of his home traps, one pinning an elephant an the other pinning a horse.

The strategic objectives of the midgame were, for Fritzlein, to break one of the frames, and for PMertens, to create an opportunity for his elephant to attack the pinned horse without letting his hostage horse be captured in the process. PMertens struck on move 34, but in exchange for winning one pinned rabbit and another exposed rabbit, he then had to choose between saving his own horse and allowing Fritzlein to break the pin on his elephant. PMertens chose to let go of his horse to maintain the frame, and was then able to fork the framed rabbit between his two home traps for a material balance, as of move 39, of three rabbits for PMertens and a horse and a rabbit for Fritzlein.

PMertens would have had adequate compensation for his material deficit in that he had taken one of Fritzlein's horses hostage in the melee, but PMertens miscalculated on move 39 in a way that let Fritzlein contest one of his home traps with only an elephant and a cat. Thereafter Fritzlein was able keep up the pressure until PMertens blundered a dog on move 54 while shuttling his elephant back and forth in an attempt to keep both of his home traps safe. A dozen moves after that, Fritzlein was able to overload the defense and force a rabbit to goal.

After all the wild play in the early rounds, the late-round games have tilted back towards dual-lone-elephant rabbit pulling contests. Does this merely reflect the style of the players who have survived, or is it an indication that multi-piece opening attacks are unsound after all? It will be interesting to see whether offensive or defensive openings rule in the 2007 Postal Tournament.

In the prediction contest, 99of9 tried to make a move by betting the minimum on PMertens while the other top four favored Fritzlein. This dropped 99of9 to fifth place, from where it would take a large swing to get back into the prediction money prizes (1st-3rd place). Fritzlein also lost ground by betting the minimum on himself and taking a long time to win. Janzert pulled a bit ahead of Ron_Weasley, and narrowed the gap to Ultra_Weak to only 121 points, so Janzert can still win by strongly betting the opposite of whatever Ultra_Weak bets on the final game. The trouble for Janzert is that Ultra_Weak must guess wrong, and in any case doesn't have to tell anyone who he is betting on until after the championship game is over! Ultra_Weak 3674; Janzert 3543; Ron_Weasley 3506; Fritzlein 3422; 99of9 3365.

Round 8

Although chessandgo was seeded fourth at the beginning of the tournament, his rating rose enough mid-tournament to make him a clear second, which also reflected the consensus view of his true playing strength. After his disappointing loss by disconnection to Fritzlein in round five, it was very satisfying that he would have a chance to re-match Fritzlein for the Championship.

Fritzlein used the initiative of the first move to pull chessandgo's eastern flank rabbit to the third rank, but in exchange chessandgo was able to force Fritzlein's two horses and camel all onto the west half of the board. Fritzlein managed to get at least his camel back over to the east, whereupon chessandgo promptly advanced a horse in the west, threatening a rabbit pull where neither Fritzlein's camel nor his elephant could defend.

In order to retain a lead in the rabbit pulling-race, Fritzlein went after chessandgo's exposed rabbit with his camel in the east. When chessandgo threatened the advanced camel, Fritzlein was able to rescue it while pulling the rabbit, but only at a cost of decentralizing his elephant in a way that allowed chessandgo to advance his camel in the west, joining his advanced horse for a powerful attack on Fritzlein's western home trap.

Fritzlein's elephant made it across to the west just in time to stave off material loss, and to cut off chessandgo's camel from taking a horse hostage. Chessandgo stationed his advanced horse behind Fritzlein's western trap, and advanced his western flank rabbit, which in conjunction prevented Fritzlein from making a useful hostage out of the camel he had cut off, and indeed threatened to tie down Fritzlein's elephant while freeing chessandgo's elephant for attack elsewhere.

In response, Fritzlein's camel captured the rabbit it had dragged in the east, and starting trying to cross over to help get the west back under control. Chessandgo complicated by pushing first Fritzlein's dog, then Fritzlein's horse over to chessandgo's side of the board. Fritzlein erred under pressure and hung a cat, but then, after a horse trade, got chessandgo's camel hostage in the west.

Fritzlein's dog was still exposed in the center, which prompted Fritzlein to advance his remaining horse. Chessandgo took the opportunity to trade his hostage camel for Fritzlein's exposed horse in a way that also threatened Fritzlein's exposed dog. Chessandgo's flank rabbit in the west, still lurking from its earlier advance, forced Fritzlein to compromise his defense in the west in order to save his dog. Thus chessandgo, at the material disadvantage of horse and cat for camel and rabbit, got excellent compensation in the form of a strong western goal attack.

With action focused around Fritzlein's western trap, chessandgo threw EHDRR into his attack, while Fritzlein tried to regain some control with his elephant and camel. Several turns later chessandgo managed to win a dog in the northwest for a rabbit in the southeast, leaving the material imbalance at HDC for MRR, the same rare material imbalance jdb and omar had. Fritzlein also shut down chessandgo's western goal threat and got the attacking dog hostage with his camel, but this proved of little value as chessandgo quickly freed the dog with his elephant, and forced Fritzlein's camel into an awkward defensive position. Meanwhile chessandgo took one of Fritzlein's rabbits hostage in the west, effectively tying down Fritzlein's elephant to defense.

While chessandgo shifted his dog and elephant to the center, Fritzlein tried to free his camel, but his elephant remained stuck. Eventually Fritzlein had to give up on his rabbit to counter chessandgo's goal threat in the east. Now at a material disadvantage, Fritzlein opted to capture a dog while allowing chessandgo a strong goal attack. The attack was stronger than Fritzlein had realized, as chessandgo forced a goal two moves later, but even with a more accurate move from Fritzlein, chessandgo's attack in the east would have been very difficult to stop.

Thus chessandgo won the 2007 Arimaa World Championship, becoming the fourth champion in four years to have learned the game less than a year prior to taking the crown. He didn't rely merely on his own accurate play and opposing blunders, but rather played imaginatively throughout, freely mixing attack and defense, and creatively sacrificing material for attacking possibilities when necessary. He defeated all of the top three seeds, as well as the second-place finisher PMertens. Chessandgo finished undefeated over the board, with his only loss due to Internet disconnection.

In the prediction contest, 99of9 was the only one of the top players to bet on chessandgo, and only one of four players overall to do so. He scored the maximum 200 points by not only wagering 100% on chessandgo, but also by exactly predicting the actual game length of 49 moves. This vaulted 99of9 from fifth to second. Ron_Weasley slipped from third to fifth by wagering a bit more on Fritzlein than the other top predictors. The "final" standings were: Ultra_Weak 3653; 99of9 3565; Janzert 3474; Fritzlein 3450; Ron_Weasley 3437.

After the game, most everyone was shocked to realize that, by rule, the prediction contest was not over, because the tournament was not over. Since PMertens and Fritzlein ended tied for second place with identical 5-2 records, the rules stipulated a one-game playoff to determine second/third place. Since this extra game was evidently part of the tournament, the director ruled that it must count towards the prediction standings. Therefore Ultra_Weak must try to hang on to the top spot for one last game before winning wire-to-wire.

Second Place Game

Fritzlein opened very loose, attacking with a horse on each flank and pulling a rabbit on each side. On move seven, however, he neglected to defend his home trap, which allowed PMertens to not only win a free rabbit, but also bust open Fritzlein's position. However, given his newfound advantage, PMertens also played quite loose and soon gave up a camel hostage. PMertens allowed his camel hostage to be captured for only a horse in exchange, but in addition he also got Fritzlein's horse and dog in trouble. PMertens outplayed Fritzlein in the unsuing mess, and won a horse for a dog and a rabbit, while keeping Fritzlein's dog as a deep hostage.

Fritzlein was then slightly leading in material at MD for HH, and captured another rabbit to increase his material lead, but allowed his camel to be taken hostage in the process. With PMertens holding a hostage at each of his home traps, Fritzlein tried unsuccessfully to dart between both and keep both the dog and the camel safe. On move 33, PMertens found a move to wall off Fritzlein's elephant and win Fritzlein's camel for nothing.

After getting behind hugely in material, Fritzlein tried to advance rabbits and complicate the game. PMertens accepted a DC for HC trade on move 40, leaving him up only H for R, but also leaving him in total control of the position. PMerterns slowly accumulated material while shutting down Fritzlein's optically scary goal threats. When Fritzlein's attack finally petered out, PMertens waltzed to goal on move 55.

PMertens performance was dominating over the board, but even more impressive considering that he played by mobile phone and got disconnected repeatedly during the game. Despite the hugely reduced thinking time, PMertens played more accurately throughout. He truly earned his second-place tournament finish, having played (and won!) more games against tough opponents than any other player.

In the prediction contest, Ultra_Weak wagered the minimum on Fritzlein, and hung on to first place by a razor-thin margin as Ron_Weasely bet the maximum on PMertens, jumping from fifth to second. Had 99of9 or Janzert been as bold, either would have taken over first, but both incorrectly backed Fritzlein, 99o9 with a moderate wager and Janzert with the maximum. The final standings were Ultra_Weak 3632; Ron_Weasley 3628; 99of9 3496; Fritzlein 3281; Janzert 3174. Congratulations to Ultra_Weak on winning the prediction contest in his very first try!