Unwed Numbers

American Scientist Online (article)

Here is an article about Sudoku and the math and logic that goes with it.

This sequence of rules suggests a simple scheme for rating the difficulty of puzzles. Unfortunately, however, not all Sudoku can be solved by these rules alone; some of the puzzles seem to demand analytic methods that don't have a clear place in the hierarchy. A few of these tactics have even acquired names, such as "swordfish" and "x-wing." The subtlest of them are nonlocal rules that bring together information from across a wide swath of the matrix.

It turns out that the math behind Sudoku is pretty complex. If you don't know what Sudoku is, you should check out this website, I'll see you back here in two to three hours...