Cage Placement Support
A digit survives only if a complete cage assignment can place it in that particular cell.
How it works
- 1Take a 2-cell cage totalling 10: its arithmetic sets are 1+9, 2+8, 3+7 and 4+6.
- 2Suppose the row already holds 1, 2 and 3 elsewhere, so neither cage cell may take those digits.
- 3The first three sets each need a digit that has no legal cell. Only 4+6 admits a one-to-one assignment.
- 4Strike 7, 8 and 9 from both cells. Those digits passed the Easy sum table, but fail the harder cell-placement proof.