[%c_effect a6;square;a6;type;Inaccuracy;persistent;true] A bit slow. Black could prepare the advance with Rb8, which is more useful, or even sacrifice the pawn.
1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. b1c3  3... f8b4  4. e2e3  4... c7c5  5. f1d3  5... b8c6  6. g1e2  6... d7d5  7. c4d5  7... e6d5  8. e1g1  8... e8g8  9. a2a3  9... c5c4 [%c_effect c4;square;c4;type;Interesting;persistent;true] An interesting idea and only the third most popular move, although it's the trendy choice at the moment. 10. d3c2 There are other options, but they do not guarantee an advantage for White. 10... b4a5 [%c_effect a5;square;a5;type;Interesting;persistent;true] 11. f2f3  11... h7h6 A theoretical novelty. A useful move, but it's not clear that it's better than the more natural 11...Re8. 12. g1h1 Preparing an aggressive plan with the g-pawn advance, especially interesting after h7-h6. 12... f8e8  13. g2g4 