1. e2e4  1... e7e5  2. f1c4 The Bishop Variation is normally used to avoid the Petroff, which has proven to be a difficult defense to break, just look at Nepomniachtchi's games. I believe Wei was not so familiar with its nuances, as he will quickly be out of the book. 2... g8f6  3. d2d3  3... f8c5 3...Nc6 and 3...c6 are also very popular. 4. b1c3  4... c7c6 Wei said he was surprised by this move. It has been played, however, in hundreds of games, including games by super-grandmasters. 5. f2f4 A brave choice for someone who doesn't know theory. 5... d7d5 Warmerdam took his time before playing this move. It's likely that he was also out of book here, or at least did not do much analysis of this position.