[%c_effect a5;square;a5;type;GreatFind;persistent;true] This move makes good use of the bishop on d7, since now White cannot return with the bishop to b5 (because of 8...Bxc3+).
1. e2e4  1... c7c5  2. b1c3  2... d7d6  3. f2f4  3... g7g6  4. g1f3  4... f8g7  5. f1b5 This move begins a more subtle way of playing the Grand Prix Attack, one of the most dangerous lines of the Sicilian. 5... c8d7 Clearly the best way to block the check. 6. b5c4 I'm not a great expert on the Grand Prix Attack and its subtleties, so I'm afraid I'd need a few hours to understand exactly what reasons lead White to leave Black's bishop on d7. Even without in-depth analysis, I will give a clue in the following moves as to what I believe to be the reason. 6... b8c6  7. d2d3 