The above constraint wants to describe what condition in the Sudoku problem?
I think the constraint here is that the numbers [MATH]1[/MATH] to [MATH]9[/MATH] appear exactly once on each square [MATH]3[/MATH]x[MATH]3[/MATH], but I think there is a small mistake in the constraint. I'm not sure either
Hope everyone helps. Thanks for very much!