Faced with the threat of Bxh7+ in the above position, an average player might see little difference between h6, g6 and Nf6 as a way to defend. A slightly better play might prefer h6 to g6, as a less weakening pawn move; and a still more observant player might decide on Nf6 because it also guards against the irritating Be4.

A better player than he, of course, would not dream of playing Nf6 without calculating the consequences of Ne4 in reply. And if this hypothetical strong player did not like what he saw after 1 ... Nf6 2.Be4, he might well decide that 1 ... h6 was best after all, even though 2.Be4 Rb8 looks a little uncomfortable.

The position comes from Michael Adams's game as Black against Maya Chiburdanidze in the England-Georgia match at the World Team Championship in Lucerne. I would love to know exactly how much Adams did calculate before opting for 9 ... h6. Had he seen that 13.Nb5 would force him either into a miserable passivity or the loss of the exchange? If so, he is to be congratulated on his excellent calculation; if not, he is to be congratulated on his inherently excellent judgement which told him that his position was sound enough to withstand a move as unusual as 13.Nb5.

In playing 13.Nb5, Chiburdanidze must have calculated that the knight could hop into a7, c6 and b8, then escape via c6. Its unstable position on that last square, however, gave Black time to pick up a pawn for the exchange.

The critical moment came after Black's 25 ... Qc6, when White's 26.f4?! overestimated her chances. The move weakens White's control of the e-file and enhances the power of the bishop on b7. The pawn belongs on f3, not f4. White's next few moves suggest the hesitancy of a player still trying to prove that she has the advantage, while not quite believing it herself. In the final stage, she was thoroughly out-calculated as Adams's d-pawn, knight and queen combined to create threats that could not satisfactorily be met.

White: Maya Chiburdanidze

Black: Michael Adams

Nimzo-Indian Defence

1 d4 Nf6 23 Rfe1 Qa8

2 c4 e6 24 Re4 Ng6

3 Nc3 Bb4 25 Ra4 Qc8

4 e3 b6 26 f4 Re8

5 Ne2 Ne4 27 Re4 Qd7

6 Bd2 Nxd2 28 Qe2 Bxc6

7 Qxd2 0-0 29 Rxc6 Rxe4

8 a3 Be7 30 Qxe4 Nxf4

9 Nf4 d6 31 b4 d5

10 Bd3 Nd7 32 Qc2 d4

11 Qc2 h6 33 Rxc7 d3

12 Be4 Rb8 34 Qc4 Qg4

13 Nb5 Nf6 35 Rc8+ Kh7

14 Nxa7 Nxe4 36 Qe4+ g6

15 Nc6 Qe8 37 Qf3 Qxc8

16 Nxb8 Bb7 38 Qxf4 Qd7

17 d5 exd5 39 Qd2 Qd4+

18 cxd5 Bg5 40 Qf2 Qd5

19 0-0 Nf6 41 Qd2 Qb3

20 Nc6 Bxf4 42 Qf2 Kg8

21 exf4 Nxd5 White resigned

22 Rac1 Nxf4