For this puzzle I had another go at this theme, with a bit of a different take:
Is it possible to reach this position in such a way that White can still castle?
Please provide your reasoning in your answer. Have fun! :)
For this puzzle I had another go at this theme, with a bit of a different take:
Is it possible to reach this position in such a way that White can still castle?
Please provide your reasoning in your answer. Have fun! :)
After a careful analysis, it becomes obvious that castling is now
possible.
The main obstacle is the promoted bishop at h7. It can only have entered its square before the g7 pawn moved to g6, so at that point, the black bishop at f8 was still on its starting square. This means the black king was still stuck on e8, and the black rook cannot have been on f8 either. Since all mobile white pieces must have been captured in order to promote the a7 pawn, we can add up all the moves that each black piece must have made after the underpromotion.
It turns out, this number exceeds the number of moves available to white's pawns, because white must have moved the e2 pawn earlier in order to allow the promoting pawn through.
Therefore,
Black must have played a move that moved two pieces at the same time!
Like so:
1. e3 a6
2. Bb5 axb5
3. Na3 Na6
4. Nc4 bxc4
5. Qe2 Nc5
6. Qd3 cxd3
7. Ne2 dxe2
8. Rg1 Nb3
9. Rh1 Nxc1
10. Rg1 Nb3
11. Rh1 Nc5
12. Rg1 Na6
13. Rh1 Nb8
14. Rg1 Nh6
15. Rh1 Nf5
16. Rg1 h5
17. Rf1 exf1=B
18. h3 Bd3
19. h4 Nxh4
20. g3 Bh7
21. f3 g6
22. f4 Bh6
23. f5 O-O!
24. g4 Kg7
25. f6+ Kxf6
26. g5+ Kf5
27. gxh6 Kg4
28. e4 Kf3
29. e5 Kg2
30. e6 Kh1
31. O-O-O+