Very interesting! Are you pauix?
Where is the king? (retrograde analysis)
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Aquest problema, no en vam parlar una altra vegada? Em sembla recordar-lo.
En tot cas és un tipus diferent de problema, que m'agradaria trobar en un diari.
Translaton: This problem, not we talk again? I seem to remember it. In any case it is a different kind of problem, I would find in a newspaper.
lalmagest wrote:
Aquest problema, no en vam parlar una altra vegada? Em sembla recordar-lo.
En tot cas és un tipus diferent de problema, que m'agradaria trobar en un diari.
This is a retrograde analysis chess problem, then it is not looking to the future (for example: How to mate in 3) but it looks to the past.
The question is simple:
In which square is the white King?
Should be analyzed where it is, and how the king has arrived here.
The problem is extracted from the book "The Chess Mysteries of the Arabian Knights",
by Raymond Smullyan.
Raymond Smullyan, a guy with a cool face
NATURAL REASONING
There are two options:
a) Or the white King is in b3
b) Or the white Bishop does check to black King
The white King can not be in a b3, otherwise would be impossible to check two pieces together: the Bishop and the black Rook. Any of these pieces could not have moved to check, because the other would be doing well check beforehand.
Therefore, the white King is not in b3 and the black King is in check.
How did the white check? With the Bishop is impossible. Then, the white King would have had to move from b3 doing a discovery check (from c2, obviously could not come).
But if it came from b3, could not be in imaginary check by Rook and Bishop also...
Therefore, this position is impossible.
SOLUTION
Well, in reality the previous reasoning is not vàlid...
Undoubtedly the white King can not now be in b3. But that does not mean they do not just come from there. Before, maybe there could be in b3.
Imagine that the white King has just captured a black piece. We put the white King in b3 and a black pawn in c3. This would be the position of the last movement.
But, how did check the black to white King? It was only possible with the black pawn on c3. They came from b4, and captured en passant the a white pawn located in c4.
Let then the black pawn on b4, and a white pawn on c4: This was the position of the previous move, where the white king chess was protected from checks of the Rook and the Bishop.
Take back another move, put the white pawn in c2. Go back one move and put the black Bishop anywhere in the diagonal h1-a8, for example in e4.
And here we have it.
The sequence of moves to reach the position where the problem is:
1..., Bd5+
2. c4, bxc3+ (en passant)
3. Kxc3+
Therefore, the white king is in c3.