In this book, devoted to Alexander Alekhine, the examples are arranged in chronological order. All the diagrams are give an additional mark - a number from 1 to 4. This classification allows the book to be used as an aid, both for trainers and teachers in lessons with theier pupils, and for independent training.
Thus players in the lower categories (Elo rating less than 2000) are initially recommended to try solving positions marked "1", and then, possibly, to test their strength in solving positions marked "2". Positions marked "2" are recommended for first category plyers (Elo rating 2000-2200) and those marked "3" for candidate masters (Elo rating above 2200). Grouped with the mark "4" are positions illustrating intuitive combinations (in which it is impossible to calculate the variations with 'mathematical accuracy' and at some point it is necessary to rely on the evaluation of the two sides' chances, suggested by your experience), positional sacrifices, and examples of tactical operations, the benefits of which must be determined by a positional evaluation of the resulting positions.