Zipper Sudoku Help
On the dashed purplish zipper line, any pair of digits that are the same distance from the central cell of the line must sum to the central cell digit.
On the image above central cell on the zipper line must be 7, it is the only available digit that can have two pairs of distinct digits that sum to it without using 1.
Zipper Sudoku Solving Strategies
Zipper line must have odd number of cells, middle cell is the sum. If other cells are in the same house (row, column, box) we can determine minimal sum.
On image below, minimum sum is 5, because we have four cells in which we can place 1, 2, 3 and 4.
If we eliminate 1 from the box, as minimal sum we have 2 + 3 + 4 + 5, which is 14. Since we have 2 pairs we can divide 14 with 2 and get 7 as minimal sum.
If Zipper pairs are not in the same house (row, box, column) Zipper sum can be as low as 3.
