1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. b1c3  4... d5c4  5. e2e4  5... b7b5 A very fresh line which was tried on a couple of occasions by Caruana. Apparently Nakamura liked  the idea and decided to give it a try.