PIENSALIA / SUDOKU EDUCATION

X-Wing Sudoku Technique

An X-Wing uses two rows and two columns to eliminate a candidate reliably.

Level: Learn the X-Wing pattern in Sudoku and use its aligned rows or columns to make reliable candidate eliminations.

Prerequisites

Know the three Sudoku rules and keep candidates consistent across each row, column, and 3 × 3 box.

How to apply it

1. Scan the relevant units and write only legal candidates.
2. Compare the positions or candidates described by the technique.
3. Make one justified placement or elimination.
4. Update related notes and rescan for new singles.

Worked example

If 4 appears only in columns 2 and 8 in rows 3 and 7, the four positions form the rectangle and other 4 candidates in columns 2 and 8 can be removed.

Common mistakes

• Guessing before checking every related unit.
• Leaving stale candidates after a placement.
• Applying a pattern without verifying all of its positions.

When to use it

Use X-Wing in advanced boards after simpler unit-based deductions stop producing progress.