Avoidable Rectangle

Avoidable Rectangle is similar to Unique Rectangle but involves solved cells. When three cells of a rectangle are already solved with two alternating values, the fourth cell must avoid completing the deadly pattern.

Technique

1. Find four cells forming a rectangle across two boxes.
2. Three corners are already solved, using two values that alternate.
3. The fourth (unsolved) cell has one of these values as a candidate.
4. Eliminate that candidate to prevent the deadly pattern that would allow multiple solutions.

Tips

• Avoidable Rectangles use the same uniqueness logic as Unique Rectangles but with solved cells.
• Types 2, 3, and 4 parallel the UR types.
• Look for rectangles where three corners are filled with two alternating digits.