Empty Rectangle

Empty Rectangle uses the absence of a candidate in a rectangular area within a box. When four cells form an empty rectangle for a candidate, combined with a strong link, eliminations become possible.

Technique

1. Find a box where a candidate forms an "L" shape (all instances in one row and one column of the box).
2. The remaining 4 cells form an empty rectangle for that candidate.
3. Find a strong link outside the box that shares a line with the non-empty row/column.
4. Eliminate from the intersection of the other strong link cell's line and the box's non-empty column/row.

Tips

• Empty Rectangles are easier to find when you look for the "L" pattern first.
• The technique exploits that the candidate must be in one of the L's arms.
• Practice identifying Empty Rectangle Intersections (ERIs).