Who would have thought that after so many years of analysis, the Grunfeld Defense would be refuted by such an innocent move $2 Of course, I'm kidding. Everything still works fine with this excellent option for Black. But White's move is still curious, especially in this move order. We will get a transposition to more conventional lines in a few moves, and the idea of the pawn advance will become clearer.
1. d2d4  1... g8f6  2. c2c4  2... g7g6  3. b1c3  3... d7d5  4. g1f3  4... f8g7 