Can a sudoku be impossible?

Related questions

1. Is there a technique to Sudoku?
2. Does Sudoku make you smarter?
3. What is a jellyfish in Sudoku?
4. Does Sudoku prevent Alzheimer's?
5. Does Sudoku improve logic?
6. Does Sudoku prevent dementia?
7. Does Sudoku stimulate brain?
8. Can all Sudoku puzzles be solved without guessing?
9. What is the technique to solve Sudoku?
10. What is the formula for Sudoku?

Tags

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2. #unsolvable
3. #committed
4. #sudoku
5. #these
6. #receive
7. #puzzles
8. #puzzle
9. #study
10. #sometimes
11. #expert
12. #consider
13. #think
14. #usually
15. #possible
16. #usage
17. #solved
18. #spotting
19. #users