Difficulty
Advanced
This is where Alternating Inference Chain normally sits in a human solving path.
Sudoku technique guide
Alternating Inference Chain Sudoku Technique
An Alternating Inference Chain uses alternating strong and weak links to prove a placement or removal. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.
At a glance
Family
Chain techniques
It belongs to the chain techniques group of Sudoku logic.
Main action
Usually remove candidates
Most technique moves reduce notes first. That often reveals a simpler placement afterwards.
What is Alternating Inference Chain?
An Alternating Inference Chain uses alternating strong and weak links to prove a placement or removal.
The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.
In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.
How Alternating Inference Chain works
- Identify strong and weak links between candidates.
- Build an alternating chain from one candidate to another.
- If the chain proves both ends cannot be false, use it to place or remove a candidate.
When to look for it
Look for Alternating Inference Chain after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.
For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.
Common mistake
AICs need exact strong and weak links. One incorrect link ruins the conclusion.
If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.
Alternating Inference Chain FAQ
What is Alternating Inference Chain in Sudoku?
An Alternating Inference Chain uses alternating strong and weak links to prove a placement or removal.
When should I look for Alternating Inference Chain?
Look for Alternating Inference Chain after simpler moves such as singles, locked candidates and obvious pairs have stopped helping.
Can SudoSketch Coach help with Alternating Inference Chain?
Yes. SudoSketch Coach can highlight candidate patterns and explain the next logical step when a Alternating Inference Chain move is available.