Sudoku Chain Rule
The basic Sudoku rules are very simple:
1. A Sudoku puzzle always must have exactly one unique solution, i.e. the Sudoku can be solved without trial and error (no guessing).
2. Each puzzle starts with some cells already filled in with a number to get you started. These numbers are called clues.
Remark: You can not change these clues. They are in the correct position to uniquely solve the puzzle. If you change them you disturb this unique solution.
3. Every group (= a coherent number of cells, e.g. a row, a column, a block) must contain each number exactly once, so without duplication anywhere in the group.
4. The numbers can appear in any order.
Tips:
5. When filling in a Sudoku accuracy is mandatory. If you fill in a number that is not correct you start a chain of mistakes in the long run you can not turn back.
Use a pencil when filling in the missing numbers, and keep an eraser at hand in the case you make a mistake.
6. Also have a look at the numbers itself: you need 9 1s, 9 2s, 9 3s etc. to solve the Sudoku. So start with the number(s) with the highest frequency.
7. So only fill in a number if you logically can prove only that number only can go to that cell. Never guess or gamble!
8. As rule of thumb you can apply: the more numbers you uniquely can fill in probably the more numbers you are going to fill in correctly, including the numbers you could not fill in earlier.
9. It should become a good habit, when filling in numbers, not only to look ahead, but also to look back. You should do this every time when you fill in a new number: by checking if you can fill in one or more numbers you could not fill in earlier.
10. Have a good look at the Sudoku puzzle and find the group(s) with the least missing numbers. Start with one of these groups to try to fill in as much of the missing numbers as you can.
11. If you get frustrated put the puzzle down, go to do something else you like to do, and come back later to this puzzle. You then probably see how to proceed where you got stuck.
Folkert van der Meulen Bosma
Folkert van der Meulen Bosma is addicted to solve Sudoku puzzles, a hobby that has become a business for him with designing and producing Challenging Sudoku Variations http://www.sudoku-variations.com.
Challenging Sudoku Variations are Sudokus with combinations of variations in grid size, block shape, number of overlapping Sudokus, symbols (numbers and letters – Wordokus), and figures and patterns.
Folkert also has designed new variations, like the 11 by 11 Sudoku with extra groups, coded word Sudokus, more words Wordokus, Sudokus with special sum groups (not the killer Sudoku), missing clues Sudoku, history Sudoku etc.