line has been played by top grandmasters such as Wesley So, Anish Giri, and Magnus Carlsen aiming for a draw. There is also the Exchange Variation where the game continues 5.cxd5 Nxd5 6. e4 Nxc3 7. bxc3 cxd4 8. cxd4, which has been used by played by the likes of Ding Liren, Anish Giri, Vladimir Kramnik, and Magnus Carlsen. Ragozin Variation: 4...Bb4 The Ragozin Variation (ECO code D37–D39) occurs after black plays 4...Bb4 in the Three Knights Variation. The Alekhine Variation of the Ragozin Variation occurs with 5.Qa4 Nc6 6.e3 O-O 7.Qc2. A transposition into the Vienna Variation of the Queen's Gambit Declined occurs with 5. Bg5 dxc4 6. e4. An alternate line commonly played is 5.cxd5 exd5 6.Bg5 h6 7.Bh4 to avoid transposing into the Vienna. Semi-Slav Defense: 4...c6 The Semi-Slav Defense occurs after black plays 4...c6 in the Three Knights Variation. Transposition into Main Variations: 4...Be7 5.Bg5 A transposition into the Main Variations of the Queen's Gambit Declined occurs after black plays 4...Be7 5.Bg5 in the Three Knights Variation. Harrwitz Attack 4...Be7 5.Bf4 This variation is also a popular line. Placing the bishop on Bg5 allows Black to exchange more freely with moves like Nf6-e4, as seen in the Lasker Defence. The move Bf4 is designed to restrict Black's opportunities in this way, as well as reducing opportunities to gain the bishop pair. Play usually continues with 5...0-0 6. e3 c5 7. dxc5 Bxc5. Peter Leko, usually an e4 player, used this variation as White to beat Vladimir Kramnik in their 2004 World Championship Match. See also Queen's Gambit Queen's Gambit Accepted References Bibliography Further reading Chess openings