Chess

This position, concocted by the Swiss problemist Markus Ott in 1980, holds the record as the longest "series-mover" - the longest problem in which one side makes all the moves to reach a specified goal. In this case, Black makes 153 moves to reach a position in which White can stalemate him in one move. The way those moves fit together - with no possibility of variation - is little short of miraculous.

To stalemate himself, Black will need to clog up all his pieces. The mechanism is not difficult to spot: With Rg4, Rhh3, Kh2, h5 and h4, all is clogged. The white rook on a2 will pin the knight on g2, but another white piece will have to prevent Kg1. White's stalemating move must be Bc5, but before that, Black will have to get rid of the pawn on d4.

Black has effectively only his king to play with. The rooks cannot escape and the knight cannot move without giving an impermissible check. Black's king must capture, in this order, the Rd3, Bd1, Nb3, Nb1, Pc3 and Pd4.

First the king must escape: 1.Rg4, 2.Rh6, 3.Kh2, 4.Kh3, 5.Kh4, 6.Kh5, 7.Rh4, 8.Rh2, 9.Kh4, 10.Kh3, 11.Rh4, 12.Rg4, 13.Kh4 and out via g7.

Moves 14 to 24 end with Kxd3, when the whole thing must go into reverse to get back for the bishop on d1. Move 36 is Kh3, when the rooks have to do their shunting manoeuvre to allow 46.Kg1 and 48.Kxd1. Then all the way back again for 74.Kxb3; another tour ends with 101.Kxb1, then 128.Kxc3, 129.Kxd4, back again for 141.Kh3, then the rooks slide in and out of g4 to permit 150.Kh2, then 151.Rh3, 152,h5 153.h4 and, at last, White plays Bc5 stalemate.

Extraordinarily, even as White's men disappear, Black's king always has only one route on the long path round the board.