Forcing Chains

Forcing Chains explore what happens when a cell is assumed to be each of its candidates. If all assumptions lead to the same conclusion, that conclusion must be true.

Technique

1. Find a cell with 2-3 candidates.
2. Assume each candidate in turn and follow the logical chain.
3. If all chains lead to the same elimination, that elimination is valid.
4. If all chains place the same digit in another cell, that placement is valid.

Tips

• Forcing Chains are powerful but time-consuming.
• Start from cells with few candidates.
• They're essentially "if-then" logic following implications.
• Consider using pencil and paper to track chains.