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

x x x  x x 5  x x x 
x x 9  x 1 x  3 x x 
x x x  4 x x  x x x 

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