Gewidmet N. Høeg
14+14. Weiß zieht und hilft Schwarz, in einem Zug mattzusetzen
Suppose white may still castle. The whole position unlocks when black
can uncapture axb. The only way this can be done is if the black rook
goes to d2, and the white knight from d2 unpromotes on a8, and goes
to a3 or a2. Retro-play would be:
-1. ... Rb7-c7 -2. Ba2-b1 Ra7-b7 -3. Bb1-a2 Ra1-a7 -4. Ba2-b1
Rc1-a1 -5. Bb1-a2 Rc2-c1 -6. Ba2-b1 b6-b5 -7. Nb1-d2 Rd2-c2 -8. Na3-b1
b7-b6 -9. Nb5-a3 d6-d5 -10. Nc7-b5 e6-e5 -11. Na8-c7 e7-e6 -12. a7-a8=N
f6-f5 -13. a6-a7 f7-f6 -14. a5-a6 g6-g5 -15. a4-a5
and black
is out of retro-moves, since both d7-d6 and g7-g6 must have been played
earlier to let out the bishops. So unlocking the position, assuming
white may still castle, fails on 1 tempo.
So white may not castle. Unlocking the position is then easy. The
white king came from f1, and the knight can unpromote on a8 without
problems then.
h#1 with 1. Ba2 Nd3#
Solution by Philippe Schnoebelen
