Originally posted by Mislav
Seems like you are right.
Sorry for posting incorrect problem.
Could this be an improvement? I think without possibility of en passant for black problem should be correct. But maybe you will refute me again.
[fen]r1b1k3/1p1p1p2/8/8/8/8/5P2/R3K2R w KQkq - 0 1[/fen]
So the reasoning goes:
- The Knights did not move at all.
- Who captured Nb1? Ra8 can never reach b1, so only Ph7 is left.
- Ph7 needs to capture at least 4 times to promote.
- White did not promote on light squares (too few captures available).
- White sacrificed 2P (e- and -g or g- and h-) and Q and B to bPh7.
- bRa8 made Black's last light-squared capture.
- After Ph7 promoted and captured Nb1, it was not captured by wQ or wB (already gone) or wP (would need to capture twice - once to kill the promoted piece, and again to be killed by bRa8). Therefore, wRh1 made the capture and returned.
- wK or wRa1 made the last capture on dark squares, then returned.
This is an easy one, because black has nothing left on light squares, and even en passant will not help white save his castling rights, because the pawn must immediately retract to its starting square, and thus it can never capture.