The game has transposed into the Exchange Variation with one little twist: the white knight is already on f3.
1. d2d4  1... d7d5  2. c2c4  2... c7c6  3. g1f3  3... g8f6  4. b1c3  4... e7e6  5. c1g5  5... b8d7  6. c4d5 This is an old method of sidestepping the Cambridge Springs Variation.