Ready to put chains into action? This page is designed for you to practice and master chains with positions from real Sudoku puzzles.
Pick X-Chain, XY-Chain or a general Alternating Inference Chain from the menu. Each board shows a chain from a real puzzle, coloured orange for true and blue for false. Tap the candidates it removes and press Check. If you’re stuck, Show me gives the answer and Next puzzle loads another. Want to watch one first? Switch to Worked example.
Quick Reminder: How do chains work?
A chain alternates strong links (only two places for a digit in a house, or only two candidates in a cell) and weak links (two candidates that see each other). If the first candidate is false, the next is true, and so on to the end. Either the first or the last candidate is true, so anything that sees both ends can be removed. An X-Chain uses one digit, an XY-Chain only bivalue cells, and an AIC mixes both.
Want a full step-by-step guide? Read the Alternating Inference Chains technique article
How to Practice
- Start at one end of the chain and follow it: orange candidates are true, blue false, so either the first or the last one is true.
- Find the candidates that see both ends of the chain (or both colours at a cell), since those can be removed.
- On the board, tap each of those candidates to remove it.
- Press Check. On your first try you see how many you found; on the second, the ones you missed get a dashed ring.
Start Practicing on Full Puzzles
Once you can find a chain on most boards without pressing Show me, take it into a full game. Evil puzzles are where this technique starts to come up, and the step-by-step solver will name the technique each time you get stuck.