Russ Abbott wrote:
Probably the biggest problem is that there are so many symmetries. The one generic rule illustrated below applies in 54 different ways, 27 horizontal and 27 vertical. And that doesn't count the symmetries (a) created by the numbers themselves or (b) by the positions in which the common numbers can appear outside the 3x3 grid or (c) by the position of the vacant square in the 3x3 grid. Yet one wants to be able to express this rule in one form and not have to re-express it multiple times. So perhaps this isn't even a good way to think about this rule--even though it is a common technique used by Sudoku players. A simpler (and more general) way to look at this rule is to notice that the cell between the 7 and the 6 is the only cell in the 3x3 sub-grid in which a 2 is valid. Will FD.distinct figure that out? If so, this deduction rule is unnecessary.
FD.distinct will not figure out, but FD.distinctD will. All the Sudoku rules that I have seen are actually special cases for FD.distinctD. This propagator supersedes all those rules!
Cheers, raph _________________________________________________________________________________ mozart-users mailing list [email protected] http://www.mozart-oz.org/mailman/listinfo/mozart-users
