Y-Wing

Y-Wing (also called XY-Wing) is the classic chain pattern. Find a 'pivot' cell with exactly two candidates {X, Y}. Find two 'wing' cells that are peers of the pivot, each with exactly two candidates: one wing has {X, Z}, the other has {Y, Z}.

Whatever the pivot turns out to be — X or Y — exactly one of the wings is forced to be Z. So any cell that sees both wings cannot be Z.

Y-Wing is the gateway to chain-based reasoning. Once you internalize it, more advanced chains feel natural.

When to look for it

Y-Wings appear once your bivalue-cell map is well-developed. Look for three bivalue cells forming a Y shape — one pivot peering at two wings.

How to apply it

1. Find a bivalue cell A with candidates {X, Y}.
2. Find a peer B of A with candidates {X, Z}.
3. Find a peer C of A with candidates {Y, Z}.
4. Z can be removed from any cell that sees both B and C.

Example