(also known as " ", " ") is a square grid, whose cells are to be filled by a range of letters (e.g. A through H), with each different letter occurring exactly once in each row and column, and the other cells remaining empty. The letters outside the grid show which letter will come across first from that direction. 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.