is played on a grid of irregular shape. Some cells of the grid contain ' ' and ' '. The task is to fill in the grid so that four consecutive identical symbols never appear in any row, column or diagonal. The puzzle book contain: - 200 Puzzles - Handy 6 x 9 inch Book Layout - 2 Puzzles per Page - Ideal for Experts In the book you will find a description and examples of solutions for all puzzles. The book is for those who like logic and math problems. Decide, developing and improving.