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What is a more difficult problem which involves using the king to prevent castling than the following problem?

White to play and win:

[FEN "r3k3/5p2/2K2P1P/b1N1P2P/8/8/4n3/8 w q - 0 1"]
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    Kb7 wins. Rd8 h7 1-0.
    – SmallChess
    May 24, 2018 at 7:33
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    @michaelc35 For future reference, try to make your question less ambiguous. It's unclear whether you're posting a puzzle for us to solve, or looking for a more complicated puzzle than the one you posted.
    – Inertial Ignorance
    May 24, 2018 at 18:19
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    I'm looking for a more complicated puzzle than the one above which I created. An idea I have is to have the rook defended so it doesn't have to worry about being captured by the king. Another idea is to have the king move which prevents castling not be the first move of the solution.
    – user11382
    May 24, 2018 at 19:12

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In this famous problem by H. Hultberg (1944), the white king castles to prevent Black from castling:

[FEN "r3k2/1p1p2p1/2pP3p/8/8/5R2/PPPP4/4K2R - - - 0 0 "]

White to mate in two moves.

According to chess problem conventions, castling is presumed to be legal unless it's provably illegal. In this position, you can prove that at least one player has lost the right to castle, but you don't know which one. (If the white rook on f3 came from a1, the white king must have moved to let it out. If the rook on f3 is a promoted piece, it must have visited a8, e8, or f8 before escaping the 8th rank, so the black king or rook must have moved.)

1.Rhf1? fails to 1...O-O-O.

1.O-O! and 2.Rf8#, as Black is now unable to castle.

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    This is an interesting problem. I would like to see a problem where the castling rights are known at the start and castling is the only move that wins and it does so by preventing castling.
    – user11382
    Aug 25, 2018 at 20:04
  • I don't understand this problem. How do we know that it's Black who has lost the right to castle, and not White (i.e. the f3-rook came from a1, White can't castle anymore, but Black can)?
    – Allure
    Sep 6, 2019 at 22:48
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    @Allure When we first look at the position, we don't know which player has lost the right to castle. After White plays O-O we know it must be Black who has lost the right to castle. I don't blame you if you consider this reasoning to be specious.
    – bof
    Sep 6, 2019 at 23:42
  • Maybe in Schrödinger's chess, but castling rights must be defined before the move takes place
    – David
    Jun 19, 2020 at 6:42
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    @David there is a convention which says that if you can’t prove whether a castling is legal, you assume that it is. There is another convention which (roughly speaking) says that if there are multiple conflicting castling rights then whoever plays it first can do so
    – Laska
    Sep 11, 2020 at 8:10
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In a comment, the OP asked for a non-retrograde analysis problem in which both castling rights are known, and, for fun, I have done so.

[Title "me, chesstackexchange.com 8/27/2019, Mate In 4"]
[FEN "4k2r/2p1p2p/P1P1P2P/8/8/8/6P1/nn2K2R w Kk - 0 1"]

Clearly, in order to checkmate Black in just four moves, White's pawn must be promoted. However, if White pushes their pawn, then Black will castle and there is no mate! Thus, White must prevent Black from castling The only way to do that is with their rook.

But if White plays 1. Rf1?, then Black will play 1... Nc2+!, also preventing a mate in time. Therefore, White's only option to prevent Black from castling is to castle themselves-1. 0-0!

Here is a shorter mate in 3 version. It shows the idea much more clearly

[Title "me, chesstackexchange.com 11/5/2019, Mate In 3"]
[FEN "4k2r/4p1p1/1P2P3/1N6/8/8/7P/n3K2R w Kk - 0 1"]
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  • One could argue that White is using the rook, not the king, to prevent Black from castling. Even if the rook arrived on f1 through a king move.
    – Evargalo
    Sep 11, 2020 at 13:37
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The answer to your puzzle is 1. Kb7 followed by 2. h7 (unless Black throws in a spite check with 1...Rb8+ or 1...Ra7+).

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