If the
In a BUG, each value that remains in a row, column or box has exactly two possible positions in that row, column or box; 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 possible way to avoid the BUG is if one of the two
The