Sly ArcadeTreat a diagonal as a complete extra unit.
An original lesson from the verified puzzle collection.
The rule
Keep the ordinary rows, columns and boxes, and use both complete corner-to-corner diagonals as extra units.
Read the constraint
Only the two marked corner-to-corner diagonals apply. A smaller parallel diagonal has no special rule. Select a diagonal cell and compare its ordinary units with the marked diagonal.
Connect the candidates
The center belongs to both diagonals. Removing one candidate there can change the available positions on two lines; explain each line separately rather than assuming all purple cells are one region.
Make a justified move
Use a diagonal hidden single when a digit has just one remaining position on that full nine-cell line. The puzzle bank requires the extra rule to contribute to the logical solution.
A real puzzle example
Open diagonal-sudoku-001, then focus on r1c8. 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 9.
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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