Game technique · Sudoku
Unique Rectangles in Sudoku
In puzzles with a unique solution, avoid a four-cell rectangle that would allow two digits to swap without changing the grid.
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In puzzles with a unique solution, avoid a four-cell rectangle that would allow two digits to swap without changing the grid.
Example
When three corners contain only the same pair, a fourth corner needs an additional candidate to break the ambiguity.
Key point
In puzzles with a unique solution, avoid a four-cell rectangle that would allow two digits to swap without changing the grid.