2024/10/03 DPA: "Castling Into Interference"

Black to move:

Material is even but Black has horrible King position and the White Rook on the 7th rank means the King cannot help the b pawn to promote.

And once White's Rook gets to b7, Black won't be able to make progress.

So, Carpe Diem ["Seize the day"]:  1. ... Rb4  2. axb4 b2.

If White makes any other move, simply push the pawn:  2. Re7 b2  3. Re1 b1(=Q)  4. Rxb1 Rxb1.

White can throw in the spite check 2. Ra8+ but 2. ... Kh7 ends that unless 3. Rh8+ Kxh8  4. bxa4 b2.

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In R+P endgames, the best defensive position is for the opponent's Rook to be behind the pawn.  In this case, White wants to play Rb7, which will make it impossible for Black to ever promote safely.

But 1. ... Rb4 solves this problem indirectly:  if 2. axb4, the White pawn now shields the Rook from attacking the pawn on the b file.  2. ... b2 and the pawn cannot be stopped.

Note that if the starting position had the pawns on the 4th rank vs the 3rd, this solution would not have worked because White would have had time to play Ra1 then Rb1.