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Similar to a previous question of mine, let's suppose there's a piece that moves like the king, but isn't restricted from moving into check.

While a normal king and two knights can't force checkmate, can this "king" and two knights force it by themselves? What about a "king" and a single knight or bishop?

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    @RemcoGerlich Kxe7 is allowed, of course. This piece is not a king--just a piece that moves like one. I don't get why this is so hard for people. And for the close voters--chess variants including nonstandard chess pieces are on-topic. Even shogi is on topic and it's far more different from standard chess than I'm proposing here. – eyeballfrog Mar 6 at 21:20
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    Then you should say so. You call it a king, your piece isn't a king, it's usually known as a Man or a Commoner. – RemcoGerlich Mar 6 at 21:24
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    @RemcoGerlich He did say so. He called the king-like moving piece a “king,” clearly indicating that it is not in fact a regular king. Proper names don’t have to be used all 100% the time. – Rewan Demontay Mar 7 at 1:23
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    @PedroA You presumably have a normal king somewhere, but the question is whether these pieces can checkmate without his help. – eyeballfrog Mar 7 at 4:46
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    @RewanDemontay: but then he has to explain how it differs from a normal king. He said it can move into check. OK, but there is also a rule that says the king cannot be captured, and he didn't say that changed as well. Hence the request for clarification. Using the proper name is just an easier shortcut. Also, what was discussed on the other question is irrelevant for this one. – RemcoGerlich Mar 7 at 6:33
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You could force a checkmate with two knights and a "king". Because the "king" does not fear being taken, it can move directly in front of the opponent's king, if it is protected by a knight. All it has to do is do this when the opponent's king is on the side of the board and thus cannot retreat - and it is known that two knights and a normal king can force the opponent's king to the side of the board.

Based on trying it out, I believe a "king" and single knight could also force checkmate. The knight supports the "king" very well, cutting off squares and proving good places for the "king" to advance. And when the knight retreats, the "king" is usually ready to go into that same square if necessary, cutting off the king and forcing it backwards.

With a bishop and a "king", I think the question is whether the king can be forced into a corner which is the same color as the bishop. The following position, with either side to move, results in a quick checkmate, because Black must go into the corner:

[FEN "1k6/8/1K2B3/8/8/8/8/8 b - - 0 1"]

I believe this can't be done from many positions, though. From most positions, the king escapes into the wrong corner. Although it can be driven from that corner, it can then flee to the wrong corner on the opposite side of the board.

  • Interesting. It seems the restriction about not moving into check hobbles the king more than I thought as an attacking piece--even a rook can't force checkmate with just a knight. I wonder what other drawn endgames become a win if the attacking side's king is replaced with a "king". – eyeballfrog Mar 7 at 8:22
  • @eyeballfrog Most pawn and king endgames become a win. Imagine a White pawn on e6 and king on d6. With a normal king, the only way Black can defend is to move his king to d8, to prevent the enemy king from advancing - but in this variation, that allows "K"d7#. With rook and pawn vs rook, Black's defense ordinarily involves as one component giving lots of checks - but now White can ignore the checks, sacrifice his "king", promote the pawn, and go into a queen and rook vs king and rook endgame, which is probably winning (although White does have to be careful not to exchange rooks). – D M Mar 7 at 12:21

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