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XY-Wing
A bivalue pivot {X,Y} sees two bivalue pincers {X,Z} and {Y,Z}. Whichever value the pivot takes, one pincer becomes Z — so any cell seeing both pincers can't be Z.
There's a move in the top-left box.
A bivalue pivot {X,Y} sees two bivalue pincers {X,Z} and {Y,Z}. Whichever value the pivot takes, one pincer becomes Z — so any cell seeing both pincers can't be Z.
There's a move in the top-left box.