Originally posted by Silent KnightBlack, Kb7-a8, white, Kd7-c8
This beautiful problem reminds me of a book by Raymond Smullyan, "The chess mysteries of Sherlock Holmes". I haven't seen it mentioned before on RHP. In it the great detective solves several mysteries using what he calls "retrograde analysis". Here's a fairly easy example:
[fen]k1K5/8/8/8/8/8/7P/6B1[/fen]
"As you see, Watson, neither side is ma ...[text shortened]... hite's last move?"
Even Watson gets it fairly quickly. Other problems are trickier.
Originally posted by Mephisto2The black king was never on a7. Hence I said king on b7 to a8, which seems to work..?
Not quite. The black king could not have come to a7 this way, allowing him to make Ka7-a8 as last move (the bishop on g1 would prevent him from doing that).
Black moved last so it must have been Ka7-a8 and therefore white must have put him in check with his previous move. The bishop can't move to give check so the only alternative is a discovered check. No piece remains and the king can't have moved to give the discovered check so the piece must have moved to a8 and been taken.
So:
0. Nb6-a8+ Ka7xa8
A simple example once you know the trick to retrograde puzzles and a good introduction to the kind of thought that goes into them.
Originally posted by XanthosNZ"Elementary, my dear XanthosNZ"
Black moved last so it must have been Ka7-a8 and therefore white must have put him in check with his previous move. The bishop can't move to give check so the only alternative is a discovered check. No piece remains and the king can't have moved to give the discovered check so the piece must have moved to a8 and been taken.
So:
0. Nb6-a8+ Ka7xa8
A ...[text shortened]... rick to retrograde puzzles and a good introduction to the kind of thought that goes into them.
Well evidently the black King moved into the corner in the last move, and since the black field he moved from is covered by a bishop, which can't be moved where it stands, a whitw pawn has been transformed to a bishop.
so g2g1B+, Ka1
so we can go without the Knight 🙂
edit: I omitted the check(+)...
Originally posted by PonderableWhite promotes on the 8th rank not the first and in FEN diagrams white always plays from the bottom.
Well evidently the black King moved into the corner in the last move, and since the black field he moved from is covered by a bishop, which can't be moved where it stands, a whitw pawn has been transformed to a bishop.
so g2g1B+, Ka1
so we can go without the Knight 🙂
edit: I omitted the check(+)...
To the best of my knowledge, FENs did not exist at the time of Holmes and Watson. But notice that in his description of the problem, Holmes says, "And we are given that your side is White". I.e., we are looking at the board from White's point of view.
After solving the problem, Watson asks if it was really necessary to know which side was White. Holmes explains that, as noted, if it is not specified there is another solution.
Originally posted by Mephisto2are you thinking white has just played b4? So if he plays it again black must capture en passent as that is his only legal move, and then Nxb3 mate
What if white retracts his last move, and has mate in two with the same move as first move? I guess that completely fulfills the request, no?