2024/06/20 DPA: "Indirect Defense, Direct Attack"
White to move.
White would like to get the Black Rook off of the d file so he can promote.
White's d pawn is en prise. White has to figure out whether this pawn is crucial to winning or can be sacrificed at the right juncture [to maybe win the Rook].
1. Rc5 Rxc5 gets the Black Rook off of the d file but 2. d7 Rd5 wins.
White can protect the pawn indirectly with 1. Rc4, as if 1. ... Rxd5 2. Ke5^ [discovered check] wins the Rook. However, I'm not sure White can win this endgame since his King will be too far away from the h1 promotion square.
And Black could just play 1. ... Kg3.
White has opposition, which constrains the Black King's mobility. Is there a checkmate threat? 1. Rc8 Rxd6 2. Rb8+ Kh4 3. Kf4
I don't see a Zugzwang.
I think I see it: 1. Rc4
- if 1. ... Kg3 2. Rd4 and if the Rook moves off of the d file, White can promote or Black will have to sac his Rook
- if 1. ... Rxd6 2. Ke5^ Kg3 3. Kxd6 Kxg2
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The key in the puzzle solution 1. ... Rxd6 is the discovered check, which allows White to win the Rook, but also that the Rook on the 4th rank and the Black King on the 2nd rank means that the King cannot guard the h pawn and White wins with 4. Rh4.
The reason it took me so long is that I didn't visualize the board after 3 moves so I didn't realize the significance of the Rook on the 4th rank.
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Yes, 1. ... Rxd6 wasn't the optimal move but it was the puzzle creator's choice to best highlight the winning idea 1. Rc4 [regardless of what Black does].
https://www.chess.com/blog/EnPassantFork/no-the-puzzle-is-not-wrong