1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... d7d5 The Queen's Gambit is an essential guest at world championships, with memorable games in the legendary clashes between Capablanca vs. Alekhine, Spassky vs. Fischer, and Karpov vs. Kasparov, among others. 4. c4d5 The exchange variation was Kasparov's favorite. 4... e6d5  5. c1g5  5... c7c6  6. e2e3  6... h7h6 In the 90s, moving the h-pawn in the Exchange Orthodox positions like this was considered an opening mistake. This is one of the clearest changes in theory in recent years. The computer showed that it's OK to play like this and also started to indicate more active plans for Black, like advancing the queenside pawns with b7-b5 and a7-a5, which was also considered anti-positional. 7. g5h4 