Empty Rectangle

In a box, if all candidates of a digit lie in one row r and one column c of that box (a cross shape; the cells of the box outside that row and column are empty of the digit), you have an Empty Rectangle.

Now find a column elsewhere where the digit has exactly two candidates, and one of them lies in row r. Let the other one be in row s. If the first end is the digit, it clears row r in the box, so the box's digit must be in column c. If the first end is false, the other end (row s) is the digit. In both cases the digit cannot be at the crossing of row s and column c (if outside the box), so remove it there. Rows and columns can be swapped.

Notation

Empty Rectangle: 1 can be removed from r5c9.