Sly ArcadeWrite possibilities, then find a reason to cross one out.
An original lesson from the verified puzzle collection.
The rule
Each row, column and 3 × 3 box contains the digits 1–9 exactly once.
Read the constraint
A note records an option, not a commitment. If a cell sees 1, 2, 4, 5, 6, 7, 8 and 9 in its row, column or box, its only candidate is 3. Read all three units before filling it.
Connect the candidates
For a hidden single, scan a whole unit for one digit. Several cells may have multiple notes, yet only one cell can hold that digit. Notes are manual; the optional candidate tool changes notes as one reversible action.
Make a justified move
Try a pair only when exactly two cells in the same unit contain the same two options. Remove those options from other cells in that unit. An uncertain digit without a rule conflict is not automatically marked wrong.
A real puzzle example
Open classic-sudoku-001, then focus on r2c3. The explanation below is generated from this puzzle’s logical proof, without looking up its answer.
Reveal the explained next step
- Every other digit is excluded by the current units and constraint candidates.
The justified digit is 6.
Practice without a penalty
Use Notes to record options. Undo restores digits and notes together. Hints reveal attention, explanation and conclusion in separate steps. All 200 puzzles are open. A daily selection is a replay from the verified pool, with its own save.
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