1. d2d4  1... g8f6  2. c2c4  2... e7e6  3. g1f3  3... d7d5  4. g2g3 The Catalan has become a powerful weapon for Nepomniachtchi. After all the work he had to do in order to play it with Black in the match against Carlsen, no wonder he decided to try it with the other color. 4... f8b4 This check is one of the most reliable options for Black. 5. c1d2  5... b4e7  6. f1g2  6... e8g8  7. e1g1  7... b8d7 The point is that the bishop is not well placed on d2 in the lines where Black refrains from taking on c4. With the bishop on c1, White can play b3-Bb2 or Qc2-Nbd2, plans that are not available now.