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Killer sudokus
H. Zantema, december 2009 – january 2010.
Just like ordinary sudokus in these puzzles numbers from 1 to 9 have to be filled in such a way that every
column, every row and every indicated 3x3 square block contains the numbers 1 to 9, each exactly once.
A group of cells containing a number means that the numbers to be put in this group sum to the given number.
It is not required that all numbers in such a group are distinct.
All puzzles have a unique solution; this has been checked by the program yices: yices proves that a formula
describing the given rules, the given sums, and a difference with the intended solution, is unsatisfiable. Most of
them I solved by hand, and I indicate whether I found them easy, medium, or hard.
1. (easy)

2. (easy)

3. (hard)

4. (easy)

5. (hard)

7. (very hard, not solved by hand)

6. (medium)

8. (medium)

9. (medium)

10. (very hard, not solved by hand)

11. (medium)

12. (medium)

13. (easy)

14. (easy)

15. (easy)

16. (easy)

17. (m