Sudoku (also known as “Number Place”) is a placement puzzle. The puzzle is most frequently a 9 x 9 grid made up of 3 x 3 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 9 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. This Sudoku variant is called Windoku (“Four-Box Sudoku”, “Hyper Sudoku”) and additionally contains four areas 3 x 3, which also contain the numbers 1 to 9 exactly once.