# Sudoku Rules

The enormous popularity of sudoku across the world is due to a couple of simple facts:

• The rules of Sudoku are straightforward.
• There are different kinds of Sudoku puzzles, from simple to tricky.
• There is a unique solution to puzzles that can be found only by applying logic. This is not a guessing game.
• Unlike mathematics, Sudoku focuses on finding patterns rather than arithmetic.
• To solve the toughest puzzles, complex strategies must be employed.

This is a conventional sudoku puzzle. In sudoku, the goal is straightforward: Fill in any row, column, or 3×3 region with the numbers 1-9 exactly once. Comparing the above puzzle to the one below will help you understand the differences. Observe that every three-by-three region, row, and column contains every number from 1-9 exactly once.

Now a solution to the same puzzle. Notes

A typical method for plotting possible numbers is to use notes (also known as mark-ups). Notes are indicated by small numbers in the image below. See the last cell on the right (the lowest). There are only three numbers that could be written in that cell, so this player has indicated these as temporary notes.