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
Salo Flohr players ever, and proved virtually invincible at the Olympiads of the 1930s. His tournament record was impressive, with his tactical skill and excellent endgame technique securing him many famous victories. FIDE awarded him the International Grandmaster title on its inaugural list in 1950. He made a number of important contributions to opening theory: a 'Flohr variation' can be found in no fewer than six major openings, including the Caro–Kann Defence, the Ruy Lopez, the English Opening, and the Grünfeld Defence. The Flohr–Zaitsev Variation of the Closed Ruy Lopez (1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0-0 Be7 6.Re1 b5