A useful move to tempt White into playing e4-e5, exchanging the light-squared bishops. Otherwise White can put the bishop on e3, develop the a1-rook, and it's not clear what Black can do in the meantime.
1. c2c4  1... g8f6  2. g1f3  2... e7e6  3. g2g3  3... d7d5  4. f1g2  4... f8e7  5. e1g1  5... e8g8  6. d2d3 I didn't know this move, which is humble in appearance, but this position has been tried many times by strong players, although overwhelmingly in rapid or blitz games. 6... c7c5 The main move. 7. f3e5 A trendy move. Giri faced this move in a classical game this year. 7... b8d7  8. e5d7  8... c8d7  9. e2e4  9... d5e4  10. d3e4  10... d7c6  11. d1e2  11... f6d7  12. f2f4 White's position already seems comfortable to me here, with more space. 12... a7a6 A new move. 13. a2a4 Useful prophylaxis against b7-b5. 13... d8c7  14. b1c3 