Unique Rectangle Type 2
Use solution uniqueness and a shared extra candidate in two corners of a rectangle to derive outside eliminations.
All candidates have been entered in the empty cells.
Assume that the puzzle has a unique solution. If extra candidate 5 is false in both cells in A, only two digits remain in the four cells. Swapping those two digits produces another solution. Therefore, candidate 5 is true in at least one cell in A. Candidates 5 marked × can be removed.