# The Rules of Sudoku

Although some Sudoku puzzles may take a lot of time and concentration to find their solution, the rules for solving them are very simple. Maybe this is one of the reasons that make Sudoku such a great game.

The sudoku grid is composed of 9 rows, sometimes labeled 'A' to 'I', 9 columns labeled 1 to 9 and 9 boxes usually marked by heavier borders.

A sudoku puzzle is solved when all the grid cells have been filled with numbers from 1 to 9 according to the following three rules:

**Each row must contain all numbers from 1 to 9**.**Each column must contain all numbers from 1 to 9**.**Each box must contain all numbers from 1 to 9**.

It follows that **any single number may appear only once in the same row, once in the same column
and
once in the same box**, or in other words **no number may appear more than once in a
row,
in a column or in a box**.

See the following puzzle solution for an example:

The unsolved puzzle showed only the givens (the numbers in black). The numbers in blue represent the solution.

As can be seen in the picture, every one of the 9 rows of the grid contains all numbers from 1 to 9 and, of course, no number is repeated.

The same can be said for every column, and every box.