1. d2d4  1... g8f6  2. c1f4 In the decisive game of the mini-match, Carlsen chooses  his beloved London System. 2... d7d5  3. e2e3  3... c8g4  4. f2f3 There is still  plenty of room for investigation in this line. A bit more than a hundred  games have been played so far. 4... g4d7  5. g2g4 The logical follow-up.  White is not only gaining space; he is also safeguarding his bishop from  the possible trade after the Nf6-h5 maneuver. 5... c7c5  6. c2c3  6... d8b6  7. d1b3  7... e7e6  8. b1d2  8... c5c4  9. b3c2  9... f8d6 As weird as this might sound, this obvious move leads to major difficulties for Black. It is, however, difficult to suggest a good plan  for Black.