http://stickman.i2p/posts/on-that-sudoku-grid.html
The Grid For those unfamiliar with Sudoku, the puzzle consists of a 9 by 9 grid of cells which is subdivided into 9 smaller
3 by 3 blocks of cells. Each cell either contains a single digit, 1 through 9, or is left blank. The goal is to
fill in all empty cells with a digit such that every row, column and block contain the digits 1 through 9 exactly
once.