Proven Sudoku
BUG-Lite
Also called BUG Lite, Partial BUG.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
The pattern applied to part of the grid rather than all of it. A small patch of squares that could be swapped is enough, and you do not need the whole board to be tidy.
The exact rule, for stronger players
The rule, stated exactly: A subgrid, rather than the whole grid, that forms a bivalue deadly pattern. The same argument applies locally.
What it removes: Remove the candidates that would complete the local deadly pattern.
Why it works: A permutable region with no external constraint would give multiple solutions regardless of the rest of the grid. This technique is only valid when the puzzle is known to have exactly one solution. It is not a deduction about Sudoku rules, it is a deduction about the puzzle setter's promise. On a grid with multiple solutions it produces wrong answers.
Worked examples
None yet. This pattern does not turn up in our daily boards, so there is no real example to show. We would rather wait than draw a fake one.
Learn these first
- Bivalue Universal GraveSay every open square had just two numbers left.
- Unique LoopLike a rectangle but longer, a ring of squares all sharing two numbers.
Related uniqueness
- BUG+1Say every open square had two numbers left, and each number had two homes in every group.
- BUG+2The same idea when two squares break the pattern instead of one.
- BUG+3The same again with three odd squares.
- Deadly PatternA shape that would give the puzzle two answers if it ever appeared.
- Extended Unique RectangleA bigger version using six squares and three numbers instead of four and two.
How often does it come up?
Our rough estimate: uncommon. Sits between the Unique Loop and the full BUG.