Stage: 3 and 4 Challenge Level:
- A clue like 2567 in cell (8,2) confirms the positions of four
of the numbers in the surrounding 3x3 square.
- It is useful to remember that the same number cannot appear in
the same row or in the same 3x3 square. This can help with a clue
such as1223 in cell (8,6) because it tells you the position of one
of the twos.