Sudoku

Test puzzle

    1 2 3   4 5 6   7 8 9
  +-------+-------+------
A | 1 7 2 | 5 4 9 | 6 8 3
B | 6 4 5 | 8 7 3 | 2 1 9
C | 3 8 9 | 2 6 1 | 7 4 5
  +-------+-------+------
D | 4 9 6 | 3 2 7 | 8 5 1
E | 8 1 3 | 4 5 6 | 9 7 2
F | 2 5 7 | 1 9 8 | 4 3 6
  +-------+-------+------
G | 9 6 4 | 7 1 5 | 3 2 8
H | 7 3 1 | 6 8 2 | 5 9 4
I | 5 2 8 | 9 3 4 | 1 6 7