This app generates puzzles with difficulty level between 0 and 20. The probability of generating sudokus with level greater than 0 is about 5%. You can save/open your sudoku. Rules applied by generator: 1. Singles. 2. Hidden singles. 3. Intersection. 4. Pairs. 5. Triples. 6. Remote pair. 7. Rectangles. 8. x-wing. 9. Hidden pairs. 10. Forcing chains. 11. xy-wing. 12. Nishio.