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 careful play White is held to gain an advantage. The best moves are 4.Nxd4 exd4 5.O-O Bc5 6.d3 c6 7.Ba4 Ne7. This defence was published in 1843 in Paul Rudolf von Bilguer's "Handbuch des Schachspiels" and explored by Henry Bird in the late 19th century. Bird played it as Black at least 25 times, scoring +9 =3 −13 (nine wins, three draws, thirteen losses). Bird's Defence was later used a few times in tournament play by Siegbert Tarrasch, Boris Spassky, and Alexander Khalifman. Although it is still sometimes seen as a surprise weapon, no strong master since Bird has adopted