The main line of the Grünfeld, the Exchange Variation ("ECO" codes D85–D89), is defined by the continuation 4. cxd5 Nxd5 5. e4. Now White has an imposing looking centre – and the main continuation 5... Nxc3 6. bxc3 strengthens it still further. Black generally attacks White's centre with ...c5 and ...Bg7, often followed by moves such as ...Qa5, ...cxd4, ...Bg4, and ...Nc6. White often uses his big centre to launch an attack against Black's king. One subvariation, frequently played by Karpov, including four games of his 1987 world championship match against Kasparov in Seville, Spain, is the Seville Variation, after 6...Bg7 7.Bc4 c5 8.Ne2 Nc6 9.Be3 0-0 10.0-0 Bg4 11.f3 Na5 12.Bxf7+, long thought a poor move by theory, as the resultant dark-square weakness had been believed to give Black more than enough compensation for the pawn.