XY-Chain Technique: Advanced Logical Solving
The XY-Chain technique is an advanced Sudoku solving method that uses a chain of cells with exactly two candidates each to eliminate possibilities across the grid.
What is the XY-Chain Technique?
An XY-Chain is a sequence of cells where each cell has exactly two candidates (X and Y), and the Y candidate of one cell becomes the X candidate of the next cell in the chain.
Key Concept: The XY-Chain technique allows you to eliminate candidates that can see both ends of the chain.
How to Identify an XY-Chain
Look for these patterns:
- Cells with exactly two candidates each
- A chain where Y of one cell = X of the next cell
- Cells that can see both ends of the chain
Solving Process
When you find an XY-Chain:
- Identify the chain of cells
- Mark the X and Y candidates
- Find cells that can see both ends
- Eliminate the common candidate
Example Scenario
If you have a chain: Cell A (1,2) → Cell B (2,3) → Cell C (3,4), and a cell can see both A and C, you can eliminate candidate 1 from that cell.
Advanced Applications
The XY-Chain technique often leads to:
- Naked singles
- Hidden singles
- Other advanced techniques
- Chain reactions of eliminations
Practice Tips
To master the XY-Chain technique:
- Practice on expert-level puzzles
- Look for cells with exactly two candidates
- Use pencil marks to track all possibilities
- Combine with other advanced techniques