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When a digit's only possible cells inside a row or column all sit in the same 3×3 box, that digit can be eliminated from the rest of that box.

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.

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.

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 digit (1–9) a cell could still legally hold — one not yet ruled out by anything in its row, column, or 3×3 box. Every empty cell has between one and nine.

A digit pre-filled into a cell at puzzle start — a clue placed by the puzzle's setter. Givens cannot be changed by the player; the rest of the grid has to be solved around them.

Two digits whose only possible cells inside a unit are the same two cells — even if those cells still show other candidates. The digit-first sibling of the naked pair.

A digit with only one possible cell within a unit (row, column, or 3×3 box) — even if that cell could legally hold other digits. The unit-first sibling of the naked single.

Three digits whose only possible cells inside a unit are the same three cells — even if those cells still show other candidates. The digit-first sibling of the naked triple.

In Killer Sudoku, when two cells in the same unit are confined to the same two-digit pair by their cage's arithmetic — eliminating those digits from elsewhere in the unit.

In Killer Sudoku, when three cells in the same unit are confined to the same three-digit set by their cage's arithmetic — eliminating those digits from elsewhere in the unit.

Two cells in the same unit whose candidate sets are identical and contain exactly two digits. Together they claim those digits across that unit and rule them out elsewhere.

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.

Three cells in the same unit whose candidates collectively use only three digits. Together they claim those digits across the unit and rule them out elsewhere.

A small handwritten or app-rendered note inside a cell indicating which digits the cell could still legally hold. The visible representation of a cell's candidate set.

When a digit's only possible cells inside a 3×3 box all share a row or a column, that digit can be eliminated from the rest of that row or column outside the box.

In Killer Sudoku, the fact that every row, column, and 3×3 box must sum to 45 — because 1+2+…+9 = 45. The foundational arithmetic identity behind most killer techniques.

In Killer Sudoku, cage sums whose cell count and total leave only one possible digit set. The arithmetic shortcut behind most killer pair and triple deductions.

Collective name for a row, column, or 3×3 box — the three groupings Sudoku's no-repeats rule applies to. Every cell sits in exactly three: its row, column, and box.