| This is a powerful technique which tries to identify a cell which once painted, would cause two different adjacent cells to be painted (set). We know that this is not possible, hence we can instead deduce that the cell should be circled. |
In this example, we can see that if we painted either the 4 in cell (1,4) or the 3 in cell (2,5), the two cells containing 8 and 6 in cells (1,5) and (2,4) would have to be circled. These would in turn force the 8 and 6 in cells (1,1) and (2,1) to be painted - an impossible situation as two painted cells cannot be adjacent.
Hence the cells containing 4 and 3 in (1,4) and (2,5) must be circled. |
