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
World Chess Championship 2013 that yield counterplay and make an exchange of rooks acceptable. After 60.Ra4, Carlsen's pawn sacrifice 60...h3 turned his f-pawn into a decisive passed pawn, and Anand resigned a few moves later. In the opening, Anand exchanged his bishop for a knight, which led to a structure similar to that of the Exchange Variation of the Ruy Lopez where Black has doubled pawns. Carlsen defended accurately, and after further exchanges the two players settled for a repetition of moves around move 30. Carlsen opted for 1.e4 for the first time in the match and the game developed into a Ruy Lopez,