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Sudoku strategy guide

Forcing chains: compare every branch

A forcing chain begins from a candidate choice and follows its logical consequences. A conclusion is safe only when every possible branch reaches it.

Key idea

If either value of the starting bivalue cell forces candidate Z into a peer of the target, Z can be removed from that target.

See the move, step by step

Branch from the 5/7 cell at R1C3 and follow both paths to candidate 6.

Step 1 of 4

Choose a controlled branch point

R1C3 has exactly two candidates, so the analysis has two exhaustive cases.

Branch regions

Step 2 of 4

Trace both implications

If R1C3 is 5, R1C4 is forced to 6. If R1C3 is 7, R2C3 is forced to 6.

Branch regionsTwo forcing paths

Step 3 of 4

Find the shared result

R2C4 sees both possible forced 6s, so it cannot contain 6 under either branch.

Forcing chainsCandidate to remove

Step 4 of 4

Keep only the branch-independent conclusion

Remove 6 from R2C4. Do not place any assumption candidate unless one branch was disproved.

Forcing chainsUpdated target

Try it on today's puzzle

Use the shortest exhaustive branch you can find. Write down each inference and accept only conclusions shared by every starting case.

Play today