1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... f8b4  4. d1c2 A principled line in the  Nimzo-Indian defense which has been tested at world championship matches. 4... e8g8  5. a2a3  5... b4c3  6. c2c3 