Black to play. Geller–Sveshnikov, USSR Ch 1978. Geller’s last move, 34 Rb1-e1 looked clever, since Black cannot safely capture the queen. But Sveshnikov’s next move exposed a critical flaw in Geller’s idea. What did he play? Answers should be emailed to chess@spectator.co.ukby Monday 30 July. There is a prize of £20 for the first correct answer out of a hat. Please include a postal address.

Last week’s solution 1 Rh1 Qe8 2 Ke1 Qa8 3 Kf1 Qa6+ 4 Kg1 and Black cannot progress, since 4…Qc4 is stalemate.

Last week’s winner Jon Pepper, East Grinstead, West Sussex