A Small Chess Puzzle, Answered
So … that puzzle.
White to play and win
The first move is relatively easy to find.
- a7! (Threatening to queen the pawn)
The obvious reply does not work.
- … Rg8?
- Bg3+ And either the rook must take the bishop (and the pawn queens), or the bishop moves to B8, protecting the pawn.
So, the entire threat is based on the unfortunate position of Black’s King, as Pedro pointed out.
Black can counter with a few checks, and if White isn’t careful, Black wins.
- … Rg1+
- Ka2 Rg2+
- Ka3? Rg8!
- Bg3? Rxg3+ and now Black wins by going back to g8 after white moves
(Even if White avoids Bg3? now Black can play …Ra8 and ….Rxa7 to draw).
After I had been shown that response (…Rg1+) I started thinking again about handling it, and I got it eventually.
- a7! Rg1+
- Be1! Rxe1
- Kb2 Re2
- Kb3 Re3
- Kb4 Re4
And Black’s King is again in an unfortunate position. Note that White must not stay on the A column (although Ka2 is ok) because if (for example, 5. Ka4 then …Re1 6. a8=Q Ra1+ wins the Queen)