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'The Logic of Sudoku' Resources Page

From, the puzzle solver's site
Welcome to the "Logic of Sudoku" resource page.

To start with I have listed the exercises in the book with links to printable versions - in case you'd like to print them out instead of working in the book.

The second set of links are to my Step by Step solver for some of the puzzles and exercises in the book. This, I hope, will allow you to see the examples as the come about. In some cases some strategies might need to be turned off to allow the example to find the use of a particular strategy, but in most cases I have picked examples for the book that are necessary steps.

Any feedback or comments always appreciated.

Andrew Stuart

Printable Exercises The following are the exercise puzzles in the book. You can click on the links to get a printable version of each puzzle.

The following are the Sudoku puzzles in the book. You can click on the links to get a printable version of each puzzle or load the puzzle into Andrew Stuarts Step-by-Step solver

Hidden Pairs - page 20
The sentence immediately under the diagram should read "1 and 5 occur in only two cells in box 2, but they are hidden by the 3 and 8 in C4 and the 3/7/8 in C6". Also the diagram 6.2 should show 1/5 in C4/C6, not 5/8.

Exercise 3 - Hidden Pairs
There is a small error on the exercise answer. One of the Hidden Pairs has been incorrectly highlighted. The fifth one, the {3/9} in box six is the correct Hidden Pair, not the {3/9} in box 8.
Correction to Exercise 3

Figure 22.2 on page 63
Unfortunately Figure 12.2 was substituted in place of the actual figure for 22.2. The real diagram is:

Figure 22.2

Table on page 123
The Extended Aligned Pair table on page 123 doesn't contain the strikethroughs which remove certain pair combinations and show how 3 can be removed. The corrected table is:
Table p123

Table on page 183
In the chapter 44, Killer strategies, is the list of cages with a unique combination of numbers. The correct table is here:
Unique Killer Cages
Note: Cages of size 7 were not included since they do not appear in most Killer Sudoku puzzles, but
41 = 2/4/5/6/7/8/9
42 = 3/4/5/6/7/8/9
A full list of all combinations is here: /Killer_Combinations.

If anyone wishes to comment, correct or contribute to these pages please feel free to contact me at I'm always interested to hear from other Sudoku fanatics.

Andrew Stuart

Exercise 5 - Simple Chain / Colouring

I've received some emails about the difference between the solver and the solution published as exercise 5 in the book. This diagram to the right is currently how the solver sees the situation.

Exercise 5
Exercise 5 : Load Example

The book shows the elimination at G2 which the solver also shows and I have drawn with blue lines. What is missing from the book solution is the other two eliminations based on different chains. But it must be remembered that Simple Chains and Simple Colouring are two sides to the same coin. The solver uses Colouring to get rid of as many candidates as possible in a single move - but each elimination can be justified by a different chain. The red and green eliminations (and the blue) occur because the 9 can see cells with different colours.

There is a problem with the solution to exercise 5 in that I have only shown one elimination out of a possible three using chains only. That I believe arose because my solver was a more primitive version at the time of writing the book and it wasn't giving me the full picture.