Sudoku X · Hard

Naked Pair in Sudoku X

Two cells in a house that hold the same two candidates. Those two digits are theirs.

The idea

When two cells in a house hold only the same two candidates, those two digits must go in those two cells. No other cell in the house can use them.

In Sudoku X the pair can sit on a diagonal, and then those digits are eliminated from the whole diagonal.

Worked examples

2 positions from real Sudoku X puzzles on this site, the familiar case first. Step through each one: the board lights what each step talks about, and the arrows show what rules what out.

A pair in a row

Hard puzzle · Naked Pair

In row 4, look for two cells that hold the same two candidates between them.

Step 1 of 4Step 2 of 4Step 3 of 4Step 4 of 4

A pair on a diagonal

Hard puzzle · Naked Pair

Both cells of the pair are on the lit diagonal, so it is one of the houses the pair clears.

Step 1 of 5Step 2 of 5Step 3 of 5Step 4 of 5Step 5 of 5

Where it fits

HardNaked Pair is a Hard technique: Hard Sudoku X puzzles are the first to need it.

The Classic Naked Pair lesson teaches it on a plain 9×9 board. The Sudoku X overview explains the rule and the levels.

Naked Pair in the other styles: Jigsaw, Thermo, Windoku, Arrow, Kropki.

Try it on a Hard Sudoku X puzzle. Next Step points it out when it is the move.

The worked examples, every step

A pair in a row

Hard Sudoku X puzzle · Naked Pair

  1. In row 4, look for two cells that hold the same two candidates between them.
  2. R4C4, R4C8 hold only {6, 7}. Those two digits must fill those two cells, so no other cell in row 4 can use them. Nor can a cell that sees both of them: R8C8 sees R4C4 on the main diagonal and R4C8 in column 8. The arrows point to the cells that lose them.
  3. Eliminate {6, 7} from R8C8.
  4. Done: 6 is eliminated from R8C8.

A pair on a diagonal

Hard Sudoku X puzzle · Naked Pair

  1. Both cells of the pair are on the lit diagonal, so it is one of the houses the pair clears.
  2. In box 1, look for two cells that hold the same two candidates between them.
  3. R1C1, R3C3 hold only {2, 3}. Those two digits must fill those two cells, so no other cell in box 1 and the main diagonal can use them. The arrows point to the cells that lose them.
  4. Eliminate {2, 3} from R2C3, R5C5, R6C6, R8C8.
  5. Done: 3 is eliminated from R2C3, R5C5, R6C6, R8C8.

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