Empty Rectangle
Advanced Removes candidates Used in: Sudoku, Killer Sudoku
In one box, a digit’s candidates form an L-shaped pattern around an empty corner. Combined with a strong link for that digit elsewhere, one crossing candidate can be eliminated.
How to spot it
A box where a digit’s candidates all share one row and one column, paired with a conjugate link elsewhere.
What you can conclude
Eliminate the digit from the crossing cell the link points to.
Worked example
A box pins 7 to one row-and-column cross; a 7 conjugate pair elsewhere then knocks 7 out of the matching cell.