The Retrograde Analysis Corner
The Problemist, 1930
16+13. Who mates in 1?
Wh. caps are axPb, cxd and f4xe5. For balance, bPf7 was promoted on
f1. Position unlocks with a very precise unpinning maneuver. Retract
-1. Rf3-d3 h4-h3
-2. Rf6-f3 h5-h4
-3. Rd6-f6 h6-h5
-4. Rd5-d6 h7-h6
-5. Nb4-a2 Nc3-a2+
-6. Nc3-a4+ Bb5-a4+
-7. Rb5-d5+ Bc5-b6
-8. Qb6-a6 and everything unlocks.
Necessarily, Bl. has the move in the diagram position (and indeed
last 15 single moves are completely
determined). Therefore, mate in 1 is with 1 ... Qxa2# !!
and not the illegal 1. Rcxc3#??