Black to play. This position is from Shirov-Nakamura, Zurich 2016. Black is winning easily but now finished with a fine geometrical concept. What was the key move? Answers to me at The Spectator by Tuesday 1 March or via email to victoria@spectator.co.uk or by fax on 020 7681 3773. There is a prize of £20 for the first correct answer out of a hat.