Hidden Single
A digit with one and only one possible cell within a row, column, or box — even when that cell still has multiple candidates of its own.
Beginner sudoku technique
What it is
A hidden single appears when, inside a single unit (row, column, or box), there is only ONE empty cell that can hold a particular digit — even though that cell might still be a legal home for several other digits too. Hidden singles are harder to spot than naked singles because you're scanning by digit, not by cell. You ask: 'where can 7 go in this row?' If the answer is one cell, that cell must hold 7.
Want the full theory?
The Hidden Single guide on Sudoku247Wiki walks through the logic step by step, with worked examples, diagrams and FAQs.
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