4-Cell Chains (Column)

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.

MXQ

Introduction Initial Values Start Grid Sub RC Elimination 2-Cell Chains Strange 2C Chains Swordfish Patterns Re-Check/Refresh X-Wing Patterns 7C Swordfish 4-Cell Chains (Row) 4-Cell Chains (Col) Solution Change Tracking Re-Eng. Grids

4-Cell Chains (Column)