I got to thids point very quickly but I can go no further. I don't know if a chain is required or not. I hope someone can help mr with this. There are only 30 candidates but I am stuck. Thanks.
*-----------*
|5..|3.4|..8|
|...|5.9|...|
|..4|.8.|...|
|---+---+---|
|..2|.9.|.3.|
|..7|...|4..|
|.1.|.2.|69.|
|---+---+---|
|...|.4.|2..|
|...|6.7|...|
|8..|2.3|..5|
*-----------*
*-----------*
|5..|3.4|..8|
|.8.|5.9|...|
|..4|182|5..|
|---+---+---|
|452|796|831|
|..7|831|452|
|318|425|697|
|---+---+---|
|..5|948|2..|
|...|657|.8.|
|8..|213|..5|
*-----------*
*--------------------------------------------------------------------*
| 5 2679 169 | 3 67 4 | 179 1267 8 |
| 1267 8 136 | 5 67 9 | 137 12467 46 |
| 679 3679 4 | 1 8 2 | 5 67 369 |
|----------------------+----------------------+----------------------|
| 4 5 2 | 7 9 6 | 8 3 1 |
| 69 69 7 | 8 3 1 | 4 5 2 |
| 3 1 8 | 4 2 5 | 6 9 7 |
|----------------------+----------------------+----------------------|
| 167 367 5 | 9 4 8 | 2 167 36 |
| 129 249 139 | 6 5 7 | 139 8 49 |
| 8 4679 69 | 2 1 3 | 79 467 5 |
*--------------------------------------------------------------------*