This is the fourth book in the series World Of Sudoku. The first three books focused on the different variants of sudoku. This book contains 120 handcrafted classic sudokus ranging from moderate to tough. All the sudokus are high on aesthetics with nice logical solve paths. The book also covers various advanced strategies like x-wing, swordfish, xy-wing, unique rectangles and other techniques that are required to crack the toughest of sudokus. Another exciting feature is the online solving links with automatic answer checking enabled for each sudoku for people who like to solve sudokus online. This book is a must have in the collection of Sudoku books for the Sudoku enthusiasts.