Classic Sudoku Puzzle Books - 400 Easy to Master Puzzles 8x8 (Volume 2)

Classic Sudoku (also known as "Number Place") is a placement puzzle. The puzzle is a 8x8 grid made up of 4x2 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 8 exactly once. Each number in the solution therefore occurs only once in each of three "directions", hence the "single numbers" implied by the puzzle's name.