Forcing Chain
AdvancedUsed at: Master
An advanced technique using hypothetical chains. Starting from a cell's candidates, reasoning is carried forward step by step.
Forcing Chain — Explained
Forcing Chain uses a temporary assumption to push logic forward. You assume one candidate is true, follow the consequences with standard Sudoku rules, and look for either a contradiction or a result that appears no matter which branch you choose. That shared result is the real value or elimination.
When to Use
Most valuable in very hard puzzles when direct pattern spotting fails and you need a controlled way to convert uncertainty into proof.
Common Mistakes
Making jumps in the chain without fully justified steps. A forcing chain is only as reliable as each small deduction inside it.
Tips
Keep the branch short and documented. Start from a bivalue cell, write down each consequence clearly, and look first for contradictions or common conclusions between branches.
Forcing Chain Steps
Pick a starting cell
Choose a cell with two candidates and assume one of them.
Follow the chain
Apply basic techniques to see where the assumption leads.
Check the result
If a contradiction occurs, the other candidate is correct. If not, find common cells across both chains.