Unique Rectangle

Three corners sharing a pair would force two solutions.

Learn the Unique Rectangle Sudoku technique: three corners of a rectangle holding the same two digits let you clear the fourth.

How to use it

  1. Spot the rectangle. Find four cells in two rows, two columns and exactly two boxes where three share the same two candidates.
  2. Avoid the deadly pattern. If the fourth corner were also just those two digits, the puzzle would have two solutions — which a real puzzle never has.
  3. Clear the fourth corner. Remove both shared digits from the fourth corner, leaving its extra candidates.
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