Thanks for reply!
I generate the puzzle with:
http://act365.com/sudoku/The solution is: (but I don't understand - no logic) record marked with ***
1. The value 5 in Box [3,1] must lie in Column 3.
The value 6 in Box [3,1] must lie in Column 2.
The value 8 in Box [3,1] must lie in Column 2.
The values 3, 6 and 7 occupy the cells (3,6), (3,7) and (3,8) in some order.
The value 4 in Box [1,1] must lie in Row 3.
The values 2 and 9 occupy the cells (8,4) and (8,8) in some order.
The cell (1,9) is one of 2 candidates for the value 4 in Row 1.
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********* 2. The value 6 is the only candidate for the cell (2,8). ******
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3. The value 7 is the only candidate for the cell (1,4).
4. The value 8 is the only candidate for the cell (1,6).
5. The value 3 is the only candidate for the cell (2,6).
6. The value 5 is the only candidate for the cell (2,7).
7. The value 9 is the only candidate for the cell (7,7).
8. The value 1 is the only candidate for the cell (7,4).
9. The value 6 is the only candidate for the cell (5,7).
10. The value 8 is the only candidate for the cell (7,8).
11. The value 2 is the only candidate for the cell (8,8).
12. The value 5 is the only candidate for the cell (9,6).
13. The value 4 is the only candidate for the cell (9,8).