Sudoku is a simple puzzle with no tricks or twists built into it. In its usual form, it is made up of a nine-by-nine grid, with heavy lines dividing it into nine three-by-three boxes. The challenge is to fill the layout with the digits from 1 through 9, so that every row, every column, and every three-by-three box contains these digits, without repeating-that is, once and only once. The puzzle-maker provides some of the numbers in the layout, and these are the initial clues to be used in solving the puzzle. How is the level of difficulty determined? I am not sure, really, although the implicit principle seems to be that that the fewer the initial clues given, the harder it is to solve the puzzle. However, in having constructed many of these myself, there seems to be much more to it than that. But I can't quite get a firm grasp on the criteria that mark difficulty levels. Maybe readers of this blog can write to me about it, if they know something concrete. The one below is moderate in difficulty, in my estimation, although determining difficulty level might be more a matter of familiarity with the puzzle than anything else. If someone has never done a Sudoku puzzle, then he or she might find it hard; on the other hand, someone familiar with the puzzle genre might find it too easy.