Practise: Hidden Quad
This verified teaching position begins directly with a real Hidden Quad pattern. Follow the chain, inspect the candidates and make the deduction before you continue.
You are at the verified key position. Use a hint to follow the chain link by link when you need support.
How to spot it
List, for every missing digit in a unit, the cells where it could go. Then look for four digits whose combined cell sets cover exactly four cells. This is genuinely laborious, so it is a last resort rather than a routine check.
Put it to use
Where you will meet it
Expert grids are the only place this pattern regularly decides the solve. Bring your notes.
Play ExpertStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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