This strategy has been deprecated. It is a clear subset of other chaining strategies and does not need to be identified uniquely
The Y-Wing strategy can be extended into chains. Remember, the Y-Wing consists of a pivot cell and two pincers. We keep the principle of the pincers exactly the same. The difference is that the pivot can be replaced by locked pairs.
Our pivot chain for a Y-Wing must proceed at odd numbered cells (or even number of links). A Y-Wing is simply a chain with length = 1.
In Figure 1 we have a Y-Wing Chain marked out in green cells. The 5/7 pivot consists of three pairs of 5/7. The first 5/7 (in which ever order) is connected to the last 5/7 by a third 5/7 in the middle, and by definition this is a locked pair. If the first 5/7 is a 5 then the third one must be a 5 as well. Same goes for number 7.
Our pincer is based on the two green cells marked with a red border - the pairs 7/9 and 5/9. The principle of the Y-Wing says that any cells that both those can see we can eliminate the common number - in this case 9. The two cells marked with a red circle can be 'seen' by both and the 9 removed.
Article created on 11-April-2008. Views: 116920 This page was last modified on 6-January-2014. All text is copyright and for personal use only but may be reproduced with the permission of the author.
Copyright Andrew Stuart @ Syndicated Puzzles Inc, 2014