Sudoku Rules

It is easy to understand the basic Sudoku rules. All cells of the Sudoku field shall be filled with numbers (or sometimes letters or symbols) so that every row, every column, and every area that is hemmed with a thick line (or otherwise emphasized) contains every possible number exactly once. Most commonly a Sudoku with a size of 9x9 cells is played. This will be filled with numbers from 1 to 9 and it contains 9 smaller squares of 3x3 cells. To make these rules somewhat clearer, you will find here examples of numbers that were placed against rules:

On the left, a second 9 was entered into a column that already contained a 9. The picture in the middle shows a 3x3 square with a second 9 and on the right you find a row that contains more than one 9. These pictures were created with the MaaTec Sudoku program using the 'Metal & Metal' board graphic. As you can see, one advantage of playing Sudokus on a PC is that numbers that were placed against the rules are immediately marked by the program.

Of course, it would be a bit boring (though not unambitious) to simply fill empty 9x9 fields. That's why Sudoku puzzles contain some cells with visible numbers. A good Sudoku will display at least so many numbers that it has only one possible solution. In this form these puzzles were first published under the name 'Number Place' by the Dell Magazine in the USA. This idea was then adopted by the japanese publisher Nikoli who also changed the name of these puzzles to 'Sudoku'. In this word 'Su' stands for 'number' and 'Doku' for 'single'. It is an abbreviation of the earlier name 'Suuji wa dokushin ni kagiru' which means something like 'that number is limited only single'. Nikoli still owns the trademark for the name 'Sudoku' in Japan. So other companies there use the original name 'Number Place' to publish Sudoku puzzles. Nikoli later added the rule that the visible numbers need to be arranged in symmetrical patterns.