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Use pencil notes with confidence
Pencil notes record possible digits, not confirmed answers. For an empty cell, remove every digit already present in its row, column, or box. Write the candidates that remain. After confirming a digit, remove it from the notes in all connected cells. Recheck notes when you erase an answer; stale notes can conceal a valid possibility.
A checked example
Row 1, column 7 takes 3. Every other digit is already excluded by its row, column, or box.