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[Myth Jellies]

Quick and efficient xy-wing searches

I thought I would port this posting of mine over from the Players Forum. Note that an xy-wing consists of three bivalued cells, two of which see the same middle cell. The content of the cells is something like ab, bc, ac.

I use a staged search for xy-wings.

First search for two cells of an xy-wing in each box. If your two cells do not share a row or column, then this tends to be your most fruitful pairing since it maximizes your opportunities for completing the xy-wing (24 cells) and it has the maximum number of cells where a reduction can take place once the xy-wing is completed (5).

In the grids below, the starred cells in the first grid indicate where you can search for a cell containing (ac) which would complete the xy-wing, and the minus signs in the next grid indicate cells where a reduction caused by the completed xy-wing can take place. If your middle cell is (ab) then you eliminate c's from the reduction cells. Otherwise, your middle cell is (bc) and you eliminate a's from the reduction cells

[Marty R.]

Thanks. Good info.

[TexCat]

Thank you! It seems so easy on a grid with only *'s and -'s. I wonder why I have so much trouble spotting them in a real grid.