Proven Sudoku
Hidden Subset (general form)
Also called Hidden Set, Concealed Subset, Subset (hidden).
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Some numbers in a group have only a few homes left. If there are as many numbers as homes, those homes belong to them. Rub every other number out of those squares.
The exact rule, for stronger players
The rule, stated exactly: For a house H and an integer n from 1 to 4, if n digits are collectively confined to the same n cells of H, all other candidates may be eliminated from those n cells.
What it removes: Remove all candidates outside the n digits from the n cells.
Why it works: n digits must be placed in H and have only n cells available, so those cells hold exactly those digits.
Worked examples
These come from real Proven Sudoku boards. Nobody drew them by hand to make the pattern look neat. Each one is checked first, so the board is one you could really meet, the pattern is really there, and every digit it rules out is really wrong.
Learn these first
- Hidden PairTwo digits in one group can only go in the same two squares.
Related subsets
- Hidden TripleThree digits in a group can only go in the same three squares.
- Locked PairA pair that shares two groups at once, usually a row and a box.
- Locked TripleA triple that sits in two groups at once, usually a row and a box.
- Naked PairTwo squares in the same group both hold only the same two digits.
- Naked QuadFour squares in one group share the same four digits between them.
How often does it come up?
Our rough estimate: umbrella page.