Brain-Training" is an innovative new series of six unique, colour illustrated puzzle books. They are designed to help you make the most of your brain power by solving puzzles that increase slowly in level of difficulty. The puzzles get progressively tougher over the six titles and range from Quick to Difficult. This allows you to plot your progress and see how well you are developing.Difficult 1 and 2 contain a high concentration of tough puzzle-types - stimulating and very useful for development - like Killer Sudoku, More Than Sudoku, Trios, Kakuro, Lateral Thinking, and Yudoku. By the time you reach book 2 you'll be ready for the extremely tough challenges that await.Buy them one by one and progress slowly, or work your way the entire series as fast as you can - the pace is up to you, but one thing is for sure, you will notice an improvement in your puzzle-solving abilities.