Internet retros-list, July 1995
7+10. Shortest possible mate? (Patrol chess)
Black can't castle: (1) Assume Black
did just move. Then the last move was done by Black King or Rook as
(under the Patrol condition) retracting any pawn capture is not possible,
(2) Assume White did just move. Again, with the Patrol condition White cannot uncapture any Black unit and retracting any White move does not help Black w.r.t. his castling rights.
Therefore it is not legal to play 1 ... O-O-O 2. a8=Q#. The shortest possible mate is 1 ... Kd8 2. Rb3 Kc8 3. Rb8#.