Chess: Fork formula leaves play balanced on knife edge

HOW TO overcome a persistent fork nuisance is the theme of today's position, a study by V Korolkov and L Mitrofanov. With White to play and draw, it starts in a rather implausible mess, but the play quickly settles into a groove.

White is a knight down and his rook on a6 is attacked. So all he needs to do is get the rook out of the way, then take the knight, and all will be well. White has three plausible opening moves, f4+, Re6+ and Rb5+, so our first job is to dismiss two of them.

1. f4+ would be fine after 1 . . . Kd4 2. Rxa4+, but 1 . . . Kd5] settles matters since 2. Rb5+ is met by Nc5. Equally, 1. Re6+ Kd5 quickly runs out of steam. But 1. Rb5+ does look promising. After 1 . . . Rd5? 2. f4+ Kd4 3. Rxa4+ White is doing very well, while 1 . . . Kd4 2. Rxa4+ picks off the knight next move.

It is time for Black to come up with a bright idea. After 1. Rb5+, he plays 1 . . . Nc5] so that after 2. Rxc5+ Kd4 White has both rooks attacked. Now comes the aforementioned fork nuisance: after 3. Raa5, Black can fork the rooks with b6, while 3. Rc4+ Kxd4 4. Raa4, sets them up for being hit with b5. So which offers a chance of survival? Continuing the latter line, White can play 5. Rc3+ Kxd2 6. Raa3, but the persistent pawn pushes on with b4 when there is no escape. It therefore has to be 3. Raa5, when 3 . . . b6 can be met by 4. Rxf5] Rg7+ 5. Rg5 and White saves his rook. But Black can avoid this with the clever 3 . . . Rg7+] saving b6 for next move.

Now we have the formula for the answer: 4. King somewhere, b6 5. Rc4+ Kxd3 6. Raa4 b5 7. Rc3+ Kxd2 8. Raa3 b4 and now with White unable to stave off loss of a rook for any longer, we need an idea, and that idea has to be a stalemate, which can only happen if White's king is blocking the f-pawn. So the fourth move had to be Kf4, and the rest just needs a moment of inspiration: 9. Rc5] bxa3 10. Rd5+] Rxd5 draw.