by eleven » Wed Jul 09, 2008 2:36 pm
The quick answer is, the trivalue cell only can be a candidate, which appears exactly 2 more times in the same row, column and box. If the grid is reduced correctly, this should only be the case for one of the 3 candidates.
So if you have listed all appearances of 235 in box 2, it only can be the 3.
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[code]grid line 1
grid line 2
...
[/code]
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