Thermo · Extreme

XY-Wing in Thermo Sudoku

A two-candidate pivot and two wings: whichever digit the pivot takes, one wing holds the third digit.

The idea

An XY-Wing is a pivot {X, Y} and two wings it sees, {X, Z} and {Y, Z}. One wing must be Z, so a cell that sees both wings cannot be Z.

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.

Pivot and wings

Extreme puzzle · XY-Wing

R1C4 (teal) has just two candidates: 2 and 3.

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

Where it fits

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

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

XY-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

Pivot and wings

Extreme Thermo puzzle · XY-Wing

  1. R1C4 (teal) has just two candidates: 2 and 3.
  2. It sees two cells (green): R7C4 with {2, 8} and R3C6 with {3, 8}. If the pivot is 2, R7C4 becomes 8; if it is 3, R3C6 does. Either way one green cell is 8.
  3. A cell that sees both green cells cannot be 8. Eliminate 8 from R2C4, R7C6, R8C6.
  4. Done: 8 is eliminated from R2C4, R7C6, R8C6.

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