Originally posted by heinzkat
Hmm... I do know this one:
[fen]7k/8/8/8/8/8/8/5R1K w - -[/fen]
White to move and mate; only the last move may be with the Rook (all others must be King moves)
1. Kh2 (takes opposition)
White plays to retain opposition. If 1...Kg8 2. Kg2 Kh8 3. Kf3. As long as black stays on the h-file, white can stay on the f-file, eventually forcing mate on the h-file, where as if black stays on the g-file, white does the same, with the opposition and eventually white will play Kg6 when black is on g8 and black plays Kh8 then Rf8 mate.