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 especially if Black plays ...Bb7. White usually plays 9.h3 instead of 9.d4 (the Yates Variation) because after 9.d4 Bg4 (the Bogoljubow Variation), the pin of the white is troublesome. The variation takes its name from the game Capablanca–Bogoljubow, London 1922. The Chigorin Variation was refined by Mikhail Chigorin around the turn of the 20th century and became the primary Black defence to the Ruy Lopez for more than fifty years. With 9...Na5 Black chases the white bishop from the a2–g8 diagonal and frees the c-pawn for queenside expansion. After 10.Bc2 c5 11.d4 the classical Black follow up is 11...Qc7, reinforcing