Ready to put the BUG+1 into action? This page is designed for you to practice and master BUG+1 with positions from real Sudoku puzzles.
Every board above is a position from a real puzzle where a BUG+1 is the next step. Select the cell, press its digit (on the pad or your keyboard) and press Check. If you’re stuck, Show me gives the answer and Next puzzle loads another. Want to watch one first? Switch to Worked example.
Quick Reminder: What is BUG+1?
A Bivalue Universal Grave is a position where every empty cell has exactly two candidates and every candidate appears twice in each house. That position has no unique solution. In BUG+1, just one cell has three candidates; the digit that appears three times in that cell’s row, column or box must be placed there.
Want a full step-by-step guide? Read the BUG+1 technique article
How to Practice
- Check that every empty cell has two candidates except one, which has three.
- In that cell, find the digit that appears three times in its row, column or box, and place it.
- Select that cell and press its digit.
- Press Check. A wrong digit is underlined in red and you can try again.
Start Practicing on Full Puzzles
Once you can spot a BUG+1 on most boards without pressing Show me, take it into a full game. Evil puzzles are where this technique starts to come up, and the step-by-step solver will name the technique each time you get stuck.