x x x  x 6 x  x x 2
6 x x  x 1 x  x 4 x
x 9 x  x x x  x x 5

1 x 3  6 9 x  x x x
x x 8  1 2 5  9 x x 
x x x  x 7 4  5 x 1

2 x x  x x x  x 1 x
x 4 x  x 5 x  x x 9
3 x x  x 8 x  x x x