User:Tentothehundred/elmo

The elmo castle (elmo囲い or エルモ囲い erumo gakoi) is a castle in shogi. This castle, created by the elmo engine, is used by the Static Rook side in games against Ranging Rook.

Summary
This castle used by the elmo engine gained attention as a new castle for the Static Rook side against Ranging Rook strategies. The elmo castle in the example on the right is composed of the King on 78, the Gold on 79, and the Silver on 68. In many cases, the right gold is moved to 59 instead of 58 for a more coherent and overall better castle made of 3 generals.

On April 1, 2020, this castle was chosen for the 47th Kōzō Masuda Award. It was the first time a shogi engine received such an honor.

With elmo's victory in the 2017 World Computer Shogi Championship and its free release, many professionals have employed it in their research. Elmo especially preferred this specific and rare formation of generals, and it was highly praised. This castle is most often used for rapid attacks in games where the Ranging Rook side has closed their bishop diagonal, especially against 3rd-file Rook. The elmo castle makes it dangerous for 3rd-file Rook to aim for the Anaguma castle, as was the trend for the past few years. It is also influenced by the idea that the Static Rook side should attack rapidly instead of engaging in battles on only one side of the board and aiming for Bear-in-the-hole.

The castle is also occasionally used against 4th-file Rook.

Below is a diagram of an usual 3rd-file Rook against elmo game. The core of the elmo castle is the Gold on 79, which protects the king's bottom. Normally, this Gold will usually be left on 69, with the right Gold moved to 58 to protect the center. However, in the future, should Gote play B-99+, aiming at 88, the King will suddenly be in danger. In comparison, with the elmo castle, 88 is protected by the Gold, and the King has ample space to escape via 69, all while being a more durable and equally simple castle overall. As for the Gold on 49, it can be moved to either 59 or 58. The traditional G-59 option creates a very strong gold-silver bond.

A structure with the gold on 79 was also used in the Shōwa era in the G-46 or Climbing Gold strategies. However, the idea behind it was to create a compact and secure structure around the king without using both Golds, which is slightly different from that of the elmo castle.

For example, the position in Example 1, a P-53 S-42 3rd-file Rook game, resulted from the moves ...P-54 S-46 S-43 P-35. Attacking on the 3rd file against 3rd-file Rook may seem counterintuitive, but Sente can pick up the pace as their King is secure. This shape is similar to that used in the S37-46 strategy against 4th-file Rook. Even if Gote's rook goes elsewhere, as long as the Gold on 49 is left as is, Sente can safely ignore Gote promoting pieces in their camp. If Gote plays ...Px35, Sx35 gives Sente a satisfactory position. It is now possible for them to attack with the Silver on the 5th rank, similar to Climbing Silver. If Gote plays ...B-42, Sente can respond with R-38.

There is also another technique. In Example 2, Gote has also played ...S-43 after Sente played P-46 trying to trade Bishops. During the opening, if Gote plays S-43 early on, this technique can still be used. The game proceeds with ...P-54 P-45. If ...Px45, Bx33+ Nx33 P-24 Px24 Rx24 and Sente has successfully broken through. Against ...S-42, after Sente's P-45 after P-46, then Bx33+ and ...Sx33, Gote can still maintain their position well. This attacking technique is only effective against Gote's ...S-43. In Example 2, if Gote plays R-42 to attack along the 4th file, Sente can play N-37 to defend and play G-59 later to avoid losing a Gold. This strategy is similar to the Fast P-45 tactic when playing against 4th-file Rook.

In this manner, in rapid attack games with elmo castles, strategy patterns change depending on the opposing tactic. As it is a new castle, there is no dedicated joseki for it, and it is expected to evolve over the coming years.