2023/10/21: "Discovered Fork"
White's Queen is en prise.
Only one check exists and it isn't a good one [1. Qxf7+].
White has a potential battery on the d file if the Bishop moves. Ideally the Bishop move would come with check and after the recapture, White could win a Rook with 2. Qxd8 Rxd8 3. Rxd8.
But the King is on a light square and the Bishop is on a dark square so that's impossible.
Is there any other move the Bishop can make to create a large enough threat such that Black doesn't capture White's Queen? I don't see one yet. 1. Bc5 forks the Rooks but Black will simply capture White's Queen. That move might be useful later, though.
White's a4 Bishop is also en prise. So if the Queen moves to avoid the Queen and Knight attack, the only place to go that defends the Bishop is 1. Qc6 [the d4 Bishop is doubly defended]. But Black can gain a tempo with 1. ... Bd7, attacking the Queen and X-Ray attacking the Bishop on a4.
1. Bxf6 Qxd5 but there is no clever Intermezzo/Zwischenzug ["in-between" move] White can do with the Bishop that allows him to win material [say, if the Black King was on h8, a dark square, White could play 2. Bxg7+ Kxg7 3. Rxd5. But even if this were possible, White's Bishop on a4 is still hanging.
1. Qc5 Rxa4 2. Bxf6 Qxf6 3. Qxc8 Rxc8 4. Rxc8+ fails because Black can block with 4. ... Bf8 and White has no dark-squared Bishop to exploit the dark square weaknesses.
The paramount factor is that White's Queen is attacked by the Knight, a lower-value piece.
I forgot to count material: dead even.
Is there a non-Queen move that allows White to create a checkmate threat that works without the Queen? I don't see one.
Black's Rook on b4 looks precariously placed. If White's Queen weren't en prise, that would be an obvious focus.
Would 1. Qa8 pose a threat? White is attacking the c8 Bishop twice but Black is currently defending it twice. 1. ... Rxa4 2. Bxf6 uncovers the Rook attacking the Queen on d8. So Black cannot recapture with the Bishop; he must recapture with the Queen 2. ... Qxf6. Now the Bishop on c8 is only singly defended.
3. Rxc8
White has won the piece back but now it's Black's turn.
1. Rxc8 loses the exchange: 1. ... Nxd5 2. Rxd8 Rxd8 and the Bishop on a4 is still en prise.
Where else can the Queen go?
- 1. Qe5 Rxa4
- 1. Qg5 doesn't threaten anything
I think I see something: 1. Qxd8 Rxd8 2. Bc5. White is looking for a variant that allows him to keep his dark squared Bishop so a Rook check that's blocked with ... Bf8 can be attacked with a Bishop on the a3-f8 diagonal.
Now Black is lost:
- 2. ... Rxd1+ 3. Rxd1 Rxa4 4. Rd8+ Bf8 5. Rxf8+ Kg7 6. Rxc8 and White has won a piece
- 2. ... Re8 3. Bxb4
- 2. ... Rxa4 3. Rxd8+
The first line is the least bad for Black so that's probably what the solution will be.
I was wrong. Black opted for 3. ... Bf8 4. Bxb4. If 4. ... Bxb4 5. Rd8+ Kg7 6. Rxc8.
I initially thought White would end up playing Bc5 and forking the Rooks with the Bishop. It turns out that White DID fork the Rooks but just not with one piece: the Bishop move attacked the b4 Rook and simultaneously uncovered an attack on the d8 Rook.
The "Discovered Fork" already exists in the lexicon so I guess I didn't "discover" anything new.
The other key in the unplayed variant is that, when the dust settled, Black's Bishop on c8, which began the puzzle doubly defended, is now hanging whereas none of White's pieces are and Black cannot get to the back rank for a checkmate in one move, giving White time to play h3, for example.
I expect the usual complaint that Black blundered by not playing the optimal 3. ... Bd7 and the usual reply is that our job is to find the best play for the solver; what the opponent does is beyond our control. If you found the idea behind 1. Qxd8 and 2. Bc5, you solved the puzzle, regardless of what the opponent does.
If the opponent blunders by playing a sub-optimal move [in this case, the difference between the top move and the 3rd choice is minimal], you as the solver need to be prepared to handle it, like a GPS that recalculates the route when the driver makes a wrong turn. The GPS doesn't get mad at the driver for being dumb.
Be like a GPS, my friend.
https://www.chess.com/blog/EnPassantFork/no-the-puzzle-is-not-wrong