This excellent chess problem was composed in 1790.

It is White’s turn to move and win. But how? Black is threatening to advance his h pawn to h1 and exchange it for a Queen. If Black succeeds in doing so, he will easily win. So White must attempt to prevent that by moving his Bishop to f3, delivering check to the Black King, forcing it to move, and then controlling the diagonal leading to the queening square h1. So, White’s first move Bf3 is obvious, and White must play it.

Black’s reply is also obvious: Kg1. From this square he can escort his h pawn to h1 and exchange it for a Queen, forcing White to exchange his Bishop for the Queen. The ensuing King and pawn game will be favourable for Black because of the positions of the pawns; Black’s pawn majority; the fact that White will need to make more moves to capture Black’s d pawn than Black will to capture White’s e pawn if the White King does not guard it; and the fact that White will have to abandon guarding his e pawn when Black gains ‘the opposition’, a position when White would be forced to move away on his turn to move.

And now a lightning bolt from White: Bh1!!! This is the key to this problem. White sacrifices his Bishop so it blocks the advance of Black’s h pawn to queen on h1, forces the Black King to capture it by Kxh1, and then traps the Black King on h1 after the White King gains ‘the opposition’ by moving to f1. Now the Black King cannot escape from the h1 square in front of his h pawn, because it would not be legal for the Black King to move into check from the White King (or vice versa).

So now, if Black cannot make a legal move, the result would be a stalemate draw. But Black can make a legal move and, because it is his turn to move, he must make it: he must move his d pawn forward to d5.

Now White’s e pawn captures Black’s d pawn and can promote to a Queen, unobstructed, after three more moves, while Black’s e pawn must make three moves before the White King can capture it on e2.

A position is then reached where the Black King can escape from in front of his h pawn; White’s d pawn queens first; Black’s h pawn queens second; but White is able to win after a series of accurately placed White Queen checks to the Black King, without Black having any opportunity to use his Queen to check the White King.

Once again, ‘the opposition’ is crucial to White winning after two Queens are on the board. The White Queen has the advantage of moving first. The Black Queen is badly placed on h1. And the King positions together with White gaining ‘the opposition’, after accurate White Queen play, leading to a win by White. BN