Thermo · Extreme

X-Wing in Thermo Sudoku

A digit locked into the same two columns by two rows, or the other way round.

The idea

If a digit can go in only two cells in each of two rows, and those cells line up in the same two columns, the rest of those columns lose it.

On a Thermo board this works exactly as in Classic. The examples are from Thermo puzzles on this site.

Worked examples

A position from a real Thermo puzzle on this site. Step through it: the board lights what each step talks about, and the arrows show what rules what out.

Two rows, two columns

Extreme puzzle · X-Wing

Look at the rows. Where does digit 4 appear?

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

Where it fits

ExtremeX-Wing is an Extreme technique: Extreme Thermo puzzles are the first to need it.

The Classic X-Wing lesson teaches it on a plain 9×9 board. The Thermo overview explains the rule and the levels.

X-Wing in the other styles: Sudoku X, Jigsaw, Windoku, Arrow.

Try it on an Extreme Thermo puzzle. Next Step points it out when it is the move.

The worked examples, every step

Two rows, two columns

Extreme Thermo puzzle · X-Wing

  1. Look at the rows. Where does digit 4 appear?
  2. Digit 4 forms an X-Wing pattern in rows 1 and 5, columns 2 and 4. Each row must place 4 in one of its two cells, so each column gets exactly one 4.
  3. Eliminate 4 from other cells in columns 2 and 4.
  4. Done: 4 is eliminated from R2C4, R4C4, R6C4.

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