1. d2d4  1... d7d5  2. c2c4  2... e7e6  3. g1f3  3... g8f6  4. b1c3  4... a7a6 [%c_effect a6;square;a6;type;Interesting;persistent;true] This is a popular variation these days. The idea is to threaten the capture of the c4-pawn, similar to what happens in the Semi-Slav Defense, which occurs after 4...c6. The difference is that, it seems, the move 5.Bg5 is worse for White in this case: Black can confidently take the c4-pawn.   So how should White defend the pawn $2 If they capture on d5 (the most popular choice), then Black clears the way for the bishop on c8. It's worth mentioning that the move a7-a6 is not a waste of time in this case, since the move has some use (for example, if White tries the famous minority attack).   If White plays 5.c5, as she does in the game, then Black can immediately break the structure with b7-b6.   In short: this move is better than it looks $1 5. c4c5  5... b7b6  6. c5b6  6... c7b6  7. c1f4  7... f8d6  8. e2e3  8... e8g8  9. f1d3  9... c8b7  10. e1g1  10... b8c6  11. a1c1 A natural move; how can you resist putting the rook on an open file $2 It's worth mentioning, however, that the creative GM Dubov tried another move and got a victory in 2021. 11... h7h6 A clever move, avoiding Bg5 once and for all. 12. a2a3 This move, however, doesn't seem convincing to me. I offer some alternatives: 12... d6f4 The first new move. 13. e3f4  13... d8d6 Black's play is natural. She attacks the f4-pawn and connects the rooks. 14. g2g3  14... a8c8  15. f1e1  15... c6e7 A bit passive. Taking the knight to c4 seems more attractive. 16. f3e5  16... c8c7  17. d1e2 