How to play Sudoku?

Sudoku is played over a 9x9 grid, divided to 3x3 sub grids called "regions".


Sudoku begins with some of the grid cells already filled with numbers:



The object of Sudoku is to fill the other empty cells with numbers between 1 and 9 (1 number only in each cell) according the following guidelines:

1) Number can appear only once on each row:


2) Number can appear only once on each column:


3) Number can appear only once on each region:


A summary of these guidelines would be, that a number should appear only once on each row, column and a region.

Source: www.sudoku.name