 Rg8 51.Nxf6 (or 51.Rg7 Nh4) Nh4!threatening 52...Qg2# (note that White cannot force mate with 52.Rh7+, since 52...Nxh7 gives discovered check by the rook).Karpov perpetrated another such swindle in the 17th game of his 1978 world championship match against Viktor Korchnoi.