🕸Fergus Duniho wrote on Sat, Feb 2, 2019 04:17 PM UTC:
The rule is borrowed from Xiangqi, but since that game doesn't include the Immobilizer, appealing to it alone cannot resolve this question. I think the usual rule in Xiangqi is that Generals may not occupy the same file with nothing in between them. But when it comes to programming Xiangqi, the simplest way to code for this is to give each General the power to capture the enemy General as a forward-moving Rook. Since they cannot move into check, this never actually results in one capturing the other, and it functions the same as a ban on occupying the same file with nothing in between.
Since the Immobilizer comes from Ultima, we might look to that game to resolve this question. Can a King occupy a space adjacent to an immobilized King in Ultima? More generally, does an Immobilizer eliminate the checking power of a piece or simply its powers of movement? Our page on Ultima does not address this issue, but Pritchard does in Popular Chess Variants. He writes, "An immobilized king can be mated by its rival moving next to it." Using this as a precedent, it looks like the Immobilizer does eliminate the checking power of a piece, and this would allow an immobilized king to be checked by the enemy King.
However, the one thing that could be said against this interpretation is that Glenn Overby writes in the "Rules of Play":
The King may never be on the same file/column as the enemy King, if there are no pieces of either color in between them.
My point here is that it is being described as a rule of the game, not simply as a description of how the King moves. This rule might be understood to override the ability of the Immobilizer to rob a piece of its checking powers. Ultimately, this may be something for Glenn Overby to rule on.
The rule is borrowed from Xiangqi, but since that game doesn't include the Immobilizer, appealing to it alone cannot resolve this question. I think the usual rule in Xiangqi is that Generals may not occupy the same file with nothing in between them. But when it comes to programming Xiangqi, the simplest way to code for this is to give each General the power to capture the enemy General as a forward-moving Rook. Since they cannot move into check, this never actually results in one capturing the other, and it functions the same as a ban on occupying the same file with nothing in between.
Since the Immobilizer comes from Ultima, we might look to that game to resolve this question. Can a King occupy a space adjacent to an immobilized King in Ultima? More generally, does an Immobilizer eliminate the checking power of a piece or simply its powers of movement? Our page on Ultima does not address this issue, but Pritchard does in Popular Chess Variants. He writes, "An immobilized king can be mated by its rival moving next to it." Using this as a precedent, it looks like the Immobilizer does eliminate the checking power of a piece, and this would allow an immobilized king to be checked by the enemy King.
However, the one thing that could be said against this interpretation is that Glenn Overby writes in the "Rules of Play":
My point here is that it is being described as a rule of the game, not simply as a description of how the King moves. This rule might be understood to override the ability of the Immobilizer to rob a piece of its checking powers. Ultimately, this may be something for Glenn Overby to rule on.