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Unique Rectangle Type 3

When roof extras combine with a naked subset.

Explanation

Type 3 treats the roof extras as one virtual cell. If those extra candidates and other cells in the same row, column, or box form a naked subset, the subset candidates can be removed from the rest of that house.

Unique Rectangle Type 3 example Sudoku board 6 3 7 9 3 7 1 8 9 4 6 5 9 2 5 1 3 7 5 2 7 2 9 7 3 5 4 4 1 7 5 9 2 3 8 2 1 7 5 4 1 5 9 6 4 2 7 6 4 9 8 5 1
An example board where Unique Rectangle Type 3 applies

Practice tip

After finding the rectangle, ignore the base pair in the roof cells and focus only on the extra notes.

Example steps

  1. Find a unique rectangle with two floor cells holding the base pair.
  2. Combine the roof extras with matching cells in one shared house.
  3. Remove the subset candidates from outside that virtual subset.

Try this technique on a real puzzle.

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