Category Archives: Extreme Solving

Extraordinary techniques deferred past advanced ones, because of effort vs. likelihood of success.

AIC Slinks Finish Only Extreme 3


This post continues the finishing coloring cluster expansion in Castillo’s Only Extreme 3, via not-both testing of AIC slinks.  After extending the blue/green cluster in the North bank via AIC slink, we continue with a second AIC slink adjoining the … Continue reading

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A Closing ALS Postscript on THLS


This post demonstrates ALS-XZ as an alternative to hidden XY chains, and concludes the review of The Hidden Logic of Sudoku by Denis Berthier. In THLS, Denis goes outside the Royles 17 collection only a few times for illustrative examples. … Continue reading

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Berthier’s xyzt Chain


This post concludes my reading of Denis Berthier’s The Hidden Logic of Sudoku, with two example puzzles to illustrate his xyzt-chain. While it is good to be aware of Berthier’s “t” versions of classic XY chains, I don’t recommend a comprehensive … Continue reading

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Berthier’s xyt-Chains Rated Extreme


This post suggests a limited role for Denis Berthier’s xyt chain in human solving. I found no THLS examples of longer chains not requiring prior xyzt or hidden chains.The last prospect, Royle 17-33442 proves to be both unjustified and unnecessary. … Continue reading

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An xyt Color Wrap


In the spirit of Valentine’s Day, I come across a coloring resource in Berthier’s xyt chain. The elaboration of Royle 17-20565 in Chapter XVII of The Hidden Logic of Sudoku is a challenge in itself. By the theory of looking … Continue reading

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Berthier’s xyt-chains in THLS


Next we review the introduction of xyt-chains in The Hidden Logic of Sudoku. These are modified XY-chains which allow extra candidates in the chain cells, and unlike regular XY-chains, make eliminations regardless of whether the chain starting candidate is true … Continue reading

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Bird’s JE Solution of Unsolvable 197


This post comments on David P. Bird’s Junior Exocet soutions of Unsolvables 190 and 197, posted in comments on Andrew Stuart’s Weekly Unsolvables page.  Bird describes his JE definition as a means of spotting exocet patterns.  However, it can  be … Continue reading

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