Nine
Naked single
Nine calls it: Only option
Only one digit still fits in a cell, because the other eight are already in its row, its column or its box. This is the technique that finishes every easy puzzle.
Example
768421125734689862537179826927343791916485432762534
The digits 1, 2, 3, 4, 6, 7, 8, 9 already appear in row 1, column 5 or the top center box. Only one digit is left: 5.
In the app
Nine is the sudoku that writes this reasoning itself, on every puzzle, in the app. The explanation fills in nothing: it names the technique, colours the proof and says why. Free for seven days, then a one-time unlock. No ads, no account, no internet needed.
Everything about Nine
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