Chess opening are so complex and theoretical that amateur players will have trouble understanding them. An example is the Perenyi Attack of the Sicilian Defense (see diagram) which yields an immensely complicated and tactical position that even strong players have difficulty handling, and that is beyond the comprehension of most amateurs. Major changes in the rules of chess in the late fifteenth century increased the speed of the game, consequently emphasizing the importance of opening study. Thus, early chess books, such as the 1497 text of Luis Ramirez de Lucena, present opening analysis, as does Pedro Damiano (1512), and Ruy López de
Ruy Lopez (also called the Flohr–Zaitsev Variation) was advocated by Igor Zaitsev, who was one of Karpov's trainers for many years. A Karpov favourite, the Zaitsev remains one of the most important variations of the Ruy Lopez. With 9...Bb7 Black prepares to put more pressure on e4 after 10.d4 Re8 11.Nbd2 Bf8 when play can become very sharp and tactical. One drawback of this line is that White can force Black to choose a different defence or allow a draw by repetition of position with 11.Ng5 Rf8 12.Nf3. Karpov tried 9...Nd7 several times in the 1990 World Championship match, but Kasparov achieved