Arimaa/risteall vs. ChrisB
This postal game was played in 2018, and features a trade of a poor horse hostage for a rabbit.
Diagram 1: the setups.
- 1g. Setting up with a decentralised camel gives Gold possibilities of quickly attacking c6. On the other hand, it gives Silver the option of taking an alignment advantage by putting both horses on the other wing.
- 1s (diagram 1). Instead Silver puts his camel on the other wing, offering a game of competing attacks. The silver camel is slightly closer to the centre, and thus slightly more flexible than the gold camel.
- 2g Ha2nnnn. In an opposite-wing attacking race, an early aim is to get a horse to a6. Gold sees nothing wrong with playing this immediately, and hopes for a chance to block the silver horse out of h3. There is no direct punishment for the horse advance, as Gold would be happy with 2s ee7swww 3g Ed2nnnn.
- 2s ee7sssw. Silver tries to gain time by blocking the development of the gold elephant.
- 3g Hg2n Cg1n Mb2n Ed2n.
- 3s hg7s mf7ws de8s. Both sides develop; Silver brings his camel one file closer to the a6 horse, threatening to hostage it.
- 4g Ha6s ra7s Ha5s ra6s. If the gold elephant were already more advanced, it would now simply block the silver camel away from the western wing. This being impossible, Gold pulls a rabbit in an effort to justify the horse advance. Although this is a standard response when the defending camel threatens an attacking horse, Gold would rather have gotten an EMH attack going. Silver has induced Gold into a less favoured plan without losing much time (playing only two sideways steps so far). This might imply that 2g was too committal, in advancing the horse before developing any other pieces.
- 4s ed4ww rf8s ra8s. Silver has a choice of plans here. Gold's rabbit pull concedes a development advantage to Silver, who could aim for an attack at f3. The relative value of the rabbit pull and the attack is unclear. Instead Silver delays the rabbit pull and threatens to flip the gold camel.
- 5g Dc2w Ed3nw Mb3e. If Gold allowed the camel to be pulled to b5, he would have to push the a5 rabbit back to unfreeze it, or allow a camel hostage. He is also wary of advancing a rabbit to b2, as Silver might pull it, interfering with Gold's rabbit pull. Gold therefore has little choice of move.
- 5s eb4s Ha4en eb3n. Silver believes that the horse-by-camel hostage will be valuable, and the best chance of compensation for the rabbit pull.
- 6g Rc1n Ec4n ra5s Hb5w. If Gold instead pushed the rabbit back to a6, his position would be fairly solid, as the a6 rabbit would make it difficult to take a horse hostage. However, Gold believes that the hostage will be bad, as Silver will have no strong piece ahead of the hostage pattern, so the silver elephant will find it hard to leave the area.
- 6s eb4n me6www. This is the only consistent move. Silver must prevent the gold horse from retreating, and not allow Gold to separate the silver camel from it.
- 7g Ra1n Db2n De2n Hg3n. It will take Silver three steps to pull the horse to a6, so the silver elephant will end the next move on b5 or b4. Gold prepares to blockade b4 or c4, keeping it from the centre. This is a standard response when an elephant is too committed to securing a horse-by-camel hostage. The rabbit step prevents the silver rabbit from advancing too far. If Gold can free his camel while maintaining a blockade of the silver elephant, he might want to attack f6; the horse step anticipates this.
- 7s mb6we Ha5n de7s. The horse hostage is not good at the moment, but Silver hopes to activate the b7 horse ahead of the hostage. It might have been better to put the elephant on b4 with the fourth step. Gold could then blockade c4, but after 8g Mc3n De3nw Rc2n 8s ra4s Db3s eb4s the silver elephant is threatening to reach c4, and Gold does not have time for the pull and replace on b6 because of the threat to the c3 rabbit.
- 8g Rb1n Db3n Rb2n Mc3n. This is the natural move, with the frozen silver rabbit as part of a blockade. Unfreezing the rabbit would be unhelpful e.g. after 8s eb5w ra4s ea5e 9g Db4w Rb3n Rc2wn the blockade is intact and the rabbit closer to being captured.
Diagram 2: after 8s.
- 8s cd8e dd7e cc7e hb7e (diagram 2). As the elephant cannot escape through c4, Silver prepares the slow plan of going through c6, aiming to preserve the hostage.
- 9g Rh2n Cd1n De3ww. It is hard for Gold to find a move here, as he must maintain the b4 blockade while anticipating the silver elephant's getting free through c6, and 9g Rb3w Db4s ra4e Ra3n 9s eb5we Ra4n rb4w is not a clear improvement. Gold brings the second dog west with a double purpose: it clarifies the position by threatening to push the silver rabbit south while maintaining the blockade, and it will allow Gold to control the rabbit with one dog while the other is free. However, later in the game the imbalance of the dogs was awkward for Gold, so this move may be a strategic mistake.
- 9s mb6n eb5ne mb7s. The elephant escapes through c6.
- 10g ra4s Db4w Rb3n Dc3w. Breaking the hostage immediately with 10g Ec5we mb6s Ha6e runs into 10s ec6e Hb6e ra7ss. Gold therefore threatens the rabbit.
- 10s ec6ess de6w. Silver prepares to defend the rabbit with his elephant.
Diagram 3: variation from 11s. Silver cannot defend the camel.
- 11g Ec5we mb6s Ha6e. It seems that Gold cannot yet capture the rabbit because of the threat to the g4 horse e.g. 11g Db3s ra3eex Db2n 11s ed4e Mc4en ee4w 12g Md5eess 12s ed4ee Hg4n ef4e. Breaking the hostage is safe because it comes with a threat to the silver camel: 11s ed4ee Hg4n ef4e 12g Mc4se 12s Hg5w eg4n Hf5nx eg5w 13g Ec5e mb5es Ed5w (diagram 3).
- 11s ra7s rb8ws ra6s. Gold would be happy at this point to have his camel in the east, so Silver would not gain anything by flipping the camel to d5 and allowing it to retreat to f3. The played exchange gives both sides some advancing steps, with Silver's perhaps the more useful.
- 12g Re1n Rh1n ra5n Da4n. Gold must keep the camel frozen, since he cannot break the hostage by flipping it: 12g Ec5n mb5ee Ec6s 12s dd6e md5nw de6w.
- 12s Mc4s ed4w de7s ce8s. Silver threatens to unfreeze the camel, and will be able to disturb Gold's southwestern position. Immediately unfreezing the camel would not work since it could be flipped to c4.
- 13g Db3s ra3e Ra2nn. Gold blockades b4 as the camel flip still seems not to break the hostage (e.g. 13g Ec5n mb5ee Ec6s 13s de6s dd6e md5n 14g Ec5n md6s Ec6e Rb4n 14s md5wn ec4n), and does so without the camel, as the camel wants to go east, ensuring Silver has no attack there and making room for the silver camel to be pushed south. Alternatively 13g Rb4w Db3n ra3e Cd2n prevents Silver's next move, but then the lack of pieces in front of the silver rabbit could be a liability e.g. 13s ec4e Db4e Cd3e ed4s 14g Dc4w Mc3n rb3e Db4s 14s Ce3n ed3e rc3x Ce4n ee3n.
- 13s Mc3e ec4sn Rc2n. This move delays the rabbit frame; also, the advanced gold rabbits are now starting to look in Gold's way.
An alternative approach was to block the gold camel from the east and try to advance there, using Gold's comparative weakness in the centre and east. 13s ec4es de6ss threatens to penetrate the gold lines with the dog, and the gold camel has trouble going east: if it moves to d4 it will be pushed to e5. Gold might be forced into messy tactics like 14g Mc3n rb3e Db2n Hg4w 14s hg6sss 15g Ec5n mb5ee Ec6s.
- 14g Rf1w Cd2w Md3e Rc3e. The camel steps east so that it cannot be pushed back to c3; the Rf1w step anticipates the silver elephant coming to c2.
- 14s ec4e Rb4es ed4w. Silver now allows the rabbit capture in order to unfreeze the camel. If instead the elephant went to c2, Gold would have to scramble to defend the south-west, which might allow the camel to be unfrozen in a better version e.g. 14s ec4s Cc2e ec3s de6s 15g Rb4e Rd3w Me3w Re1w 15s Db2s ec2w rb3ws 16g Rd1w Db1w Rc1w Cd2w 16s eb2nn Hb6n mb5n, although the details are unclear.
This possibility illustrates how much a piece in front of a horse hostage can affect the position. If Silver had had nothing in front of the hostage, the hostage would have been worthless. Gold believed that the rabbit in front would make little difference, as the rabbit was vulnerable and could not itself unfreeze the camel. However, the need to control the rabbit has restricted the gold pieces, and denied Gold room to push the camel south.
- 15g Rd3n Rc3e rb3e Db2n. The rabbit is finally framed.
Diagram 4: after 15s.
- 15s ec4w rc3x Hb6n mb5n eb4n (diagram 4). The elephant cannot return to c4 after unfreezing the camel. After 15s ec4w rc3x Hb6n mb5n eb4e 16g Ec5we mb6s Hb7s, Gold wins the repetition fight, being the first to play a reversible move; Silver's move was not reversible, as it sacrificed a rabbit. Pushing the horse to c6 seems to allow it to escape east with a good position for Gold e.g. 15s ec4w rc3x Hb6e mb5n eb4e 16g dd6s Hc6e dd5e Hd6s 16s Rd4e ec4e Hd5n ed4n 17g Ec5n mb6s Ec6w. Since Gold will be able to blockade c4, the elephant prepares to move through c6 again.
Comparing diagram 4 to diagram 2, the hostage pattern itself is now stronger, as the gold horse has moved from a6 to b7, which gives Silver the option of pushing it to b8, protecting the camel and freeing the silver horse. On the other hand, Gold is more advanced, and has captured a rabbit, which gives Gold a freer position besides the bare material value.
- 16g Ec5e Me3n Ed5w dd6s. Gold now wants to combine material threats with threats to disrupt the hostage pattern. The played move conveniently blockades d4 while threatening the dog: if the silver elephant goes to c6 immediately, the dog will be flipped to c4.
- 16s eb5s Da5e ra6s de6w. The hostage will be stronger if Silver can gain space on the a-file. This move incidentally threatens a dog frame.
- 17g Cc2nn ra5n Db5w. It would be difficult to prevent the elephant escaping via either c4 or c2; pushing the a5 rabbit back at least forces the the silver camel to move before the elephant leaves, or the camel will be pulled to b5 again. Occupying c4 prevents the elephant from reaching d4 immediately.
- 17s Hb7n mb6n eb4nn. Pushing the gold horse to b8 might be the first step towards strengthening the hostage by getting the silver horse to b6 and camel to c7. But Gold is threatening to win the d5 dog in f3, and preventing this with the other two steps is tricky. Silver could have tried leaving the elephant on b4 for a move, since the gold cat would hang after 17s Hb7n mb6n hc7sw 18g dd5e Ec5e Me4s de5s, while Silver is just in time to defend the dog after 18g Me4nn dd5e Rd3w 18s Db3w eb4sse. In the later case the gold camel might join the fight at c6 before the silver elephant returns to the centre, with a messy position which is probably good for Gold.
After the played move, Gold is clearly ahead, since he will get a material advantage worth more than the horse hostage.
- 18g dd5e Ec5e Me4s de5s. Gold threatens the silver dog. This move would not be effective were the gold horse still on b7, as the horse could then be captured in exchange for the dog.
- 18s eb6se Da5e ra6s. Silver makes a counterthreat to delay the dog capture, while again trying to gain space. 18s eb6se mb7s Hb8s would fail to 19g dd6e Ed5n Rd4n Rd3n, blocking the silver elephant from defence of the dog.
- 19g dd6e Ed5n de4e Me3n. The d6 dog is pushed east rather than west since this weakens the hostage trap.
- 19s mb7s ec5ee Rd4n. It would take Gold four steps to capture the dog and retreat both camel and horse to safety on the third rank. Silver pulls a rabbit, planning to answer the dog capture by threatening it in f6. This means leaving the horse unfrozen on b8, which will lose time if Silver later wants to threaten it, but the horse is still hostaged in a strategic sense since it probably does not have time to escape by pushing along the back rank.
This move is a mistake, however, as Gold is not obliged to capture the dog. 19s mb7s Hb8s ec5ee or 19s hc7sw mb7e Hb8s was probably better.
- 20g Cc4n ra5n Db5w Rd3n. Gold would be better after the dog capture, but it would allow Silver to secure a-file space by moving the a7 rabbit to a6, finally making the horse hostage fairly valuable. The played move prevents this, while also threatening to push the silver camel south with the elephant, taking a camel hostage around c3 in a few moves. This maneuver would be weaker with a silver rabbit on a5, since it would unfreeze the camel on b5.
Diagram 5: variation from 20s.
- 20s Me4s ee5s df4nw. Silver would need two steps to protect the hostage, and three steps to save the dog, and therefore has a choice. Preserving the hostage with 20s hc7s Cc5s hc6s cd7w 21g df4sx Hg4ws Me4s 21s ee5s Rd4s ee4w mb6n (diagram 5) leads to a position where neither side has a quick plan. The gold camel would now like to go back west to deal with the c5 horse, and it could be difficult for the free silver elephant to achieve anything while preventing this. Meanwhile Gold might make slow progress by bothering the hostage pattern, for instance moving the elephant to c5 or perhaps putting the dog on b6. Gold's western space advantage would be an asset in this fight.
Instead Silver chooses to save the dog. Although a single hostage would usually not be worth a dog, the camel push to b5 is the difference between Silver having a horse hostage and Gold having a camel hostage, so could be worth a dog in principle. In any case this move could be a practical mistake, as it simplifies the position when Gold is ahead.
- 21g Ed6w mb6s Ec6w Hb8s. Hb8s is the most natural fourth step, as the horse will be useful at c6.
- 21s de6w Rd4w ee4w rc8w. The rabbit push to c4 is intended to obstruct the camel hostage, but perhaps 21s de6ww cd7s was better, keeping the gold horse out of c7 and delaying the b3 dog's crossing the trap.
Diagram 6: variation from 22g. After a trade of camel for horse and cat, the silver elephant cannot defend c6.
- 22g Eb6ew hc7s Hb7e. Gold wants to push the camel south without leaving the b3 dog frozen. Ideally the dog will move east, starting to correct Gold's imbalance. Superficially it seems that the need to defend c6 is a direct problem, but in fact after 22g Db3ee mb5s Eb6s the c5 cat is poisoned. 22s Rc4s ed4w Cc5nx ec4n fails immediately to the fence 23g mb4e Eb5s Me3nw. A better try for Silver is 22s dd6we Cc5nx ed4e 23g mb4s Eb5s mb3ex Eb4s 23s ee4e Hg4n ef4e de5n. Gold would not be satisfied simply trading camel for horse and cat, since this trade is materially roughly equal, but the silver camel is hostaged, so Gold can hope for more. Defending the gold horse directly with 24g Me3nn de6e Me5n does not work, as after 24s eg4wwn ce7n 25g Hg5w Rc4w Eb3en 25s Me6n ee5n rf7e df6n the gold elephant is one step too slow in reaching f5. Gold can, however, make a counterthreat in c6: 24g Eb3nne Hb7s 24s Hg5w eg4n Hf5nx eg5w 25g Ec5n hc7n Ec6n Dd3n (diagram 6) seems good for Gold.
Unfortunately for Gold, Silver would not have to capture the cat. After 22s Rc4s ed4w de5n, Gold does not have time to defend c3 and c6 and also take a secure camel hostage, and Silver has some annoying threats in c6 e.g. 23g Hb7s Re2ww 23s mb4ss Cc5n ec4n. Gold decides that the problem is that his horse would be misplaced on b6, and gets it c7 immediately. The downside is that Gold spends time advancing the silver horse, which would probably want to advance soon anyway.
- 22s ed4e Rc4e Cc5s hc6s. The horse could be defended by a blockade on d7, but this is fairly pointless as it wants to advance to defend the camel hostage. Silver could delay a standard hostage pattern with 22s de5n Rd5e Cc5e hc6s 23g Db3ee mb5s Eb6s 23s Rc4s ed4w Ra4s mb4w, although this leaves the elephant blocking the further advance of the horse. Later in the game the silver elephant went to d3; it was probably better to do so immediately with 22s ed4s Rc4e Cc5s hc6s.
- 23g Db3ee mb5s Eb6s.
- 23s Me3e ee4s rb8ss. Silver defends the camel with a counterthreat to the gold camel.
- 24g Hg4ww Mf3n Re2w. Gold cannot push the silver camel south because it would lose a piece in c3 by false protection. The played move prepares a threat to the e5 dog by freezing it, while improving Gold's alignment by putting the camel near the g6 horse and horse near the silver dogs. The rabbit on d2 prevents the d3 dog from being pushed back, which aids Gold's control of c3 since there will be a blockade on c4.
- 24s Dd3w ee3w dd6w cd7s. Stuffing the c6 trap strengthens its defence and unfreezes the horse.
Diagram 7: variation from 25s.
- 25g mb4s Eb5s Re1n Rd2w. Gold could now push the camel to a3, but instead holds the hostage next to the trap. This is desirable, where the pattern can be maintained, because then the capture takes only two steps. The drawback in general is that the opponent need bring in just one more piece to free the elephant, but that is not so simple here: c4 is blockaded, and 25s ed3e Dc3e Cc4s hc5s freezes the horse and gives Gold a winning goal attack with 26g Da5e rb6n Db5n Ra4n 26s dc6s cd6w ce7sw 27g Eb4n hc4w dc5s Eb5e 27s hb4w Ra5e ha4n 28g rb7n Db6n Rb5n Ec5w (diagram 7) (or 28g Hc7e cd6e cc6x Hd7s Rc2w 28s Rb5s ha5e ra6s ce6n 29g Cc3s Rb2w Hd6n Rd5n, also winning).
Earlier in the game Gold's space advantage made it easier for Gold to fight against the horse hostage. It now strengthens the camel hostage by making it harder for Silver to advance towards c3, and giving Gold quicker threats at c6.
- 25s ed3e Rd4s He4w ee3n. It being hard to find a constructive move, Silver offers a camel trade, although this loses time: after 26g Rh3nw Mf4s Rc2e Silver probably has no better than reversing 25s on the next move.
- 26g Rd3e Dc3e mb3ex Eb4s. But gaining time is unnecessary, as tactics after the camel trade favour Gold.
- 26s Mf4n ee4e Mf5nx ef4n. Keeping the c5 horse safe takes two steps. Silver could try 26s rb6s dc6w Mf4n ee4e, but then after 27g Hd4e de5n He4n Mf5e it seems Gold will lose at most a horse in exchange for the camel.
- 27g Eb3nn Cc4w Re3n. Rabbit to e4 prevents the gold horse from being pushed to c4, blocking the capture of the c5 horse.
- 27s de5n Rd5e hc5e ef5s. This is a mistake, as b6 should have been blockaded. However, after 27s de5n Rd5e hc5e ra7e both the horse and the c6 trap remain vulnerable, for instance 28g Eb5ew hd5w Hd4n 28s hc5se Cb4e dc6s 29g Eb5s Cc4sw Eb4e 29s rb6ss cd6ww 30g Da5e cb6e Db5n Ra4n.
The alternative was to attack in the east with 27s hg6sss ef5s. Then Gold would probably not want to capture the horse immediately, but would still win it after 28g hc5s Eb5e Dd3e. Gold would have to defend for a few moves, but should be able to do so comfortably.
- 28g Eb5e Da5e rb6n Db5n. Gold's attack is crushing, as captures in c6 will come with very quick goal threats.
- 28s hg6sss ce7w. The silver elephant could probably prevent short-term goal by retreating to defend c6, but Silver's position would be hopeless, with the elephant tied to defence and the free gold elephant easily able to make more captures. Instead Silver goes for a losing race.
- 29g cd7e Hc7ew cd6n dc6x.
- 29s ef4sw Rf2nx cd7s.
- 30g Db6e Ra4nen.
- 30s cd6nnw ce7w.
- 31g cc8e Hc7n Dc6n.
- 31s rf7sss ra6s.
- 32g Dc7s rb7e Rb6nn.