*-----------*
|478|6..|..9|
|...|...|7..|
|2.6|1..|..5|
|---+---+---|
|...|..4|...|
|.1.|928|.7.|
|...|7..|...|
|---+---+---|
|8..|..5|1.7|
|..7|...|...|
|9..|..1|456|
*-----------*