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W-Wing
Two matching bivalues, tied together by a strong link on one digit.
W-Wing relies on two bivalue cells that share the same candidate set {X, Y} but aren't peers of each other. The bridge is a strong link elsewhere on X: somewhere on the board, X is confined to exactly two cells inside a single unit, one of which is a peer of bivalue A and the other a peer of bivalue B.
If A is X, the strong link forces B to also be X — impossible. So neither bivalue is X, which means both are Y. Anything that sees both bivalues can't be Y.
When the move applies
Once chain logic feels natural, scan pairs of bivalues with identical candidates that aren't directly peering at each other. Then hunt for the strong link bridging them.
The procedure
- Find two non-peer bivalue cells with identical candidates {X, Y}.
- Find a unit where X has exactly two candidates, each a peer of one of the bivalues.
- Remove Y from every cell that sees both bivalues.