Bivalue Universal Grave type 1

If the value 2 were removed from the cell D6, the Sudoku would exhibit a Bivalue Universal Grave pattern (or BUG).

In a BUG, each value that remains in a box, row, or column has exactly two possible positions in that box, row, or column; and each empty cell has exactly two potential values. A Sudoku having a BUG has zero, two or more valid solutions.

Because a valid Sudoku has exactly one solution, the BUG cannot be part of it. The only way to avoid the BUG is if the cell D6 contains the value 2. The values 7 and 8 can therefore be removed.