Probably stating the obvious here, but...
If White to move, Rxf7 is mate
If Black to move, Nb6 is mate
So it appears the puzzle is "Who's move is it".
There are a lot of pieces that "obviously" could not have made the previous move. There are a few pieces that COULD have but if they HAD it meant mate-in-one was missed.
I *think* that because white's mate doesn't work if the Knight is missing, that the LAST move was Ng5, and therefore it's black to move, and Nb6 is mate.
Well, the players are not necessarily good. All you know is that they are playing a legal game of chess, not necessarily a sound game of chess. (Heck, if it's sound, why would Black cramp all those pieces in the top-right corner?) But yes, the puzzle is "whose move is it?".
By guesswork, it's black to move, because about 90% of mate in 1 retros are black to move. :P
By seriousness, [it really is black to move, and 1...Nb6# is mate. Last 10 half moves are determined]. Analysis left for others - I don't want to spoil the frustration involved. In fact I was quite surprised to solve it as fast as I did (half an hour). Very intricate northeast cage with a number of plausible tries.
I figured it out, move the pawn up and get a knight ;)
Silvan wrote:
You will never, ever, ever figure out this really really really hard mate in 1.
@Silvan: Cooked; 1. Rc6#, 1. Rg6#, 1. Rh6#, and 1. Re5# all work in addition to 1. d8=N#. And I might be missing some more moves.
Let's see. Black is missing 2 pieces and White is missing 4 pieces. White needs at least g2xf3, and Black needs at least axbxc. One player needs to make two more captures to get rid of the c and d pawns, which must be Black because he is the only one to have two captures left. That means that Black must also capture cxd and dxc. White also has the additional possibility of capturing bxc, which would in turn allow Black to capture dxc and c5xd4 (or e5xd4).
Some possible last moves are b6xBc7, c5xd4, Nh3-g5, h5-h4, c4-c3, e5xd4, and c5xd4. However, there are some restrictions because White will need to promote the h pawn to sacrifice it. There are a few important move orders that are illustrated below. Here is me failing:
That was a good problem, well worth the time. If I'm not mistaken, each capture is uniquely determined (what died where and by which opponent piece). I won't post the solution, that would spoil it for others who wish to try.
I think 2 of the captures are not completely determined. Interchangeable captured units. But the crucial ones are determined.
(12+14) Mate in 1...by who?
Alexander Kislyak
Shakhmaty v SSSR, 1974, 1st Prize