XY-Chains link bi-value cells together to make distant eliminations.
Understanding the Concept
A chain of bi-value cells where each cell shares one candidate with the next.
Chain: {A,B} - {B,C} - {C,D} - {D,E} and so on.
If chain starts with {A,B} and ends with {Y,A}, then A can be eliminated from cells seeing both ends.
Can be any length - longer chains are harder to spot.
Very powerful but requires strong pattern recognition.
Foundation for more complex chain techniques.
Examples
Simple XY-Chain
Chain: {1,3} - {3,7} - {7,9} - {9,1}. Cells seeing both first and last cell cannot be 1.
Pro Tips
- •Start with bi-value cells
- •Follow the chain of shared candidates
- •Look for chains that loop back to starting digit
- •Practice with short chains first
