BUG+1

BUG (Bivalue Universal Grave) is a state where all cells have exactly two candidates and each appears twice per unit - creating multiple solutions. BUG+1 has one cell with three candidates; the extra candidate must be the solution.

Technique

1. Find a near-BUG state: all cells have 2 candidates except one cell with 3.
2. In the 3-candidate cell, identify which candidate appears an odd number of times in its row, column, and box.
3. That candidate (appearing 3 times instead of 2) must be the solution for this cell.

Tips

• BUG+1 is easy to spot when you're near the end of a puzzle.
• Count candidate occurrences - the "odd one out" is the answer.
• This technique assumes puzzle uniqueness.