White king on a1, Queen on b2, Knights on a2 and b1. Black king's position is unknown but legal. White to play and checkmate Black.

Note: assume this is a semi-blindfold game - White sets up his pieces as given and turns away from the board. Black then puts his King on any legal square and the game begins; White calls out his move, Black makes it for him. Black then makes his (legal) move and announces when he has done it, but, naturally, not what the move was. (Ignore the 50-move rule - my solution took 57 moves.(worst case))