Diagonal Sudoku

Keep the ordinary rows, columns and boxes, and use both complete corner-to-corner diagonals as extra units.

1. Select an empty cell, then choose a digit or switch Notes on.
2. Ask for a gentle hint: attention first, proof next, then the conclusion only when you request it.
3. Undo uncertain moves or pause. Every puzzle is open; daily selections use a separate save.

Select a cell · 1–9 fill · N notes · arrows move · Delete erase · Ctrl/Cmd Z undo

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.

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.

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.

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