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 