Sudoku is a logic game consisting of filling in a square grid of 9 x 9 cells, with numbers ranging from 1 to 9.
A number can only be present once on each row, column, and region (square subdivision of 3 x 3 cells).
Although it is not an official rule, most sudoku generators - including Foxy Sudoku's - require that the solution of the grid be unique.
The basic rules are therefore very simple. However, from these very simple rules arise a multitude of techniques for solving a sudoku..