This curious line, in which Black delays the capture of the d5-pawn, is considered by theory to be one of the best ways for Black to achieve equality in this opening.
1. e2e4  1... e7e5  2. g1f3  2... b8c6  3. b1c3  3... g8f6  4. d2d4  4... e5d4  5. f3d4  5... f8b4  6. d4c6  6... b7c6  7. f1d3  7... d7d5  8. e4d5  8... e8g8  9. e1g1 