Sudoku Tutorial
W_wing.jpg A W-wing consists of two identical bivalue cells that cannot see each other (shown in blue). They contain candidates X & Y.    These cells are the wings (or pincers) of the W wing..  

Unlike the XY wing and XYZ wing, there isn't a single base (or pivot).   A W-wing has two base cells (yellow) where:
  • They are strongly linked to each other by candidate X  (5 in this example)
  • Each base cell (yellow) is visible to one of the wings (links between base and pincers can be weak or strong)
This forces the Y candidate to be present in at least one of the wings (candidate 1 in the blue cells).     The candidate 1 (Y) can be removed from any cell that is visible to both wings (like r2c7).

(Did you notice that a W-wing is also an XY chain?)
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