Cage single
In Killer Sudoku, when a one-cell cage's sum directly forces the cell's digit. The simplest possible killer deduction — the cage's sum is the cell's value.
A cage single is the simplest deduction in Killer Sudoku. When a cage contains exactly one cell, that cell's digit must equal the cage's sum — by definition of how cage sums work. The cage is degenerate but real, and the deduction is automatic.
When it applies
Most Killer Sudoku puzzles avoid one-cell cages because they hand the player a free digit and reduce the puzzle's challenge. But some puzzles include them as starting hints, or as a natural consequence of how the cage partition was generated. When you do see one, the deduction takes a beat: a 7-cage of one cell is just a 7 in that cell.
This entry exists mostly because Sudoku Mountain's solver tracks the cage single as its own deduction label when it fires, so the solver replay can show "this digit came from a cage single" without lumping it into the broader cage completion bucket.
How it differs from a naked single
A naked single is a unit deduction — the cell's row, column, and box rule out everything except one digit. A cage single is a cage deduction — the cell's cage size and sum lock the digit directly, without reasoning about the rest of the grid. Both produce a placement; they reach the placement by different routes.
For an introduction to Killer Sudoku as a whole, see Meet Killer Sudoku.
See also
- Cage— In Killer Sudoku, a contiguous group of cells outlined by a dotted line, with a printed sum the digits inside must add up to. Replaces the classic Sudoku given.
- Cage completion— In Killer Sudoku, placing the last digit of a cage by subtracting the digits already in it from the cage's sum. The cage's leftover arithmetic does the work.
- Naked single— A cell on the Sudoku grid that has only one legal candidate left — the simplest deduction in the game, and the one that solves most of an easy puzzle.
Read more
- Meet Killer Sudoku
An introduction to Killer Sudoku for someone who knows the classic version — what changes, how the experience differs, and where to start.