MXQ Adv. Sudoku

4-Cell Chains (Column)

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In the example below, a 4-cell chain occurs in column 6. A 1, 2, 8 or 9 occur in 4 cells meaning that those digits can only occur in those column-cells: A6, B6, E6 & H6. 1, 2, 8 or 9 can be removed from all other cells in column 6: C6, G6 & I6. 4-cell chains can occur in rows, columns or blocks & highlighting does not help.

4 Cell Chains