White to play. Mamedyarov–Artemiev, MeltwaterChampions Final 2021. Black’s last move, was Ra8-a4, attacking the pawn on g4. But it allowed Mamedyarov a decisive tactical opportunity. What did he play? Answers should be emailed to chess@spectator.co.uk by Monday 11 October. There is a prize of £20 for the first correct answer out of a hat.