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📋 X-Wing – Advanced Technique

If two rows (or columns) restrict a digit to the same two columns (or rows), they form a rectangle; eliminate that digit from the other cells in those lines.

What Is X-Wing?

X-Wing occurs when, for a digit (shown with 1), two rows are restricted to the same two columns (or vice-versa: two columns restricted to the same two rows). This forms a rectangle; the digit can then be eliminated from all other cells in those columns/rows.

Step-by-Step Example

Step 1: Two rows restrict 1 to the same two columns — X-Wing rectangle
1) Spot two rows where 1s can only appear in two identical columns ⇒ X-Wing.
Step 2: Eliminate in the other rows of those columns
2) Remove 1 from the remaining rows in those columns (outside the two X-Wing rows).
Step 3: Resulting placements after eliminations
3) After the clean-up, forced placements (like a 1) usually appear.

Variants

  • Row-based: 2 rows → same 2 columns.
  • Column-based: 2 columns → same 2 rows.

Common Pitfalls

  • Allowing more than two columns/rows — the pattern must be exactly 2×2.
  • Confusing it with Swordfish (which uses three lines).

Tips

  • Light candidate marks make X-Wings easier to spot.
  • After eliminations, re-scan for singles and pairs.
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