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AIC

When strong and weak links form a general forcing chain.

Explanation

An AIC alternates strong and weak links between candidate nodes. If it starts and ends with strong links on the same digit, one endpoint must contain that digit, so common peers can remove it.

AIC example Sudoku board 4 6 7 2 5 8 1 5 7 3 8 6 8 9 1 4 7 2 8 3 2 5 1 3 5 4 6 1 8 1 2 4 8 7 6 3 9 6 4 9 9 3 8 4 2 5 4 1 6 2 9 3 8
An example board where AIC applies

Practice tip

Use AIC after simpler chains. Mix bivalue-cell links with strong unit links, and keep the links strictly alternating.

Example steps

  1. Pick a candidate node with a strong link.
  2. Alternate strong and weak links through cells and units.
  3. When both endpoints are the same digit, remove it from cells seeing both ends.

Try this technique on a real puzzle.

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