GridWits
Extreme tier Technique 33 of 46 Reference only

Forcing Nets

Forcing Chains generalized into a branching tree instead of a single line — every branch from an assumption is followed, and any conclusion every branch agrees on holds.

The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.

How it works

  1. 1Assume A1 = 3. Unlike a plain Forcing Chain — one line of dominoes — that assumption branches at once: E1 shares row 1 with A1 and A5 shares column A, so both lose their 3 and each becomes forced.
  2. 2The two branches then cascade separately, and either can fork again further out.
  3. 3If every branch of the net — however it forks — ends up agreeing E5 can't be 6, that elimination holds no matter which path the truth actually takes.

Play a Sudoku that needs this technique →

A 1 B 2 C 3 D 4 E 5 F 6 G 7 H 8 I 9 3 8 3 5 3 9 2 6 3 8 6
  • First colour in the chain
  • Cells that establish the pattern
  • Where the conclusion lands
  • Candidate ruled out
Next in the ladder Nishio Forcing Chains →

Proof by contradiction on a single candidate: tentatively assume it's true, chain the consequences forward, and if that breaks the board, it was false all along.