6...Na6 is the other main line.
1. d2d4  1... g8f6  2. c2c4  2... g7g6  3. b1c3  3... f8g7  4. e2e4  4... d7d6  5. f1e2  5... e8g8  6. c1e3 A form of the Averbakh system, where the bishop is provocatively placed on the g5-square. The oldest living GM just turned 100, and this is a good occasion to honor him $1