Advancing to LPO on Unsolvable 40

This post confirms the intractability of Andrew Stuart “Unsolvable #40” to SSOB  bv scan, X-panel analysis, coloring.  In preparation for Limited Pattern Overlay, a shortcut AIC reduces the number of patterns  for the number 8, and a coloring cluster is added for possible  restriction of these patterns.

I have little to show for my pre-LPO efforts on the  1/29/12 puzzle.  Very few bv, and consequently no bv scan results.  Also no X-panel  breaks.  The large cloud of 3-candidates washes out the bv field. Coloring was weak, and there were not many AIC hinges either.  I did find one AIC nice loop which has the happy effect of reducing the number of patterns for the number 8.


I added another cluster, with a bridge to the blue / green cluster.  Purple and green join in r7c4, making pink and blue toxic.

Lightly weighted curves remain on the grid from my efforts to put more AIC together.

Next step would be enumerating ALS and possibly Death Blossoms, with toxic set removals. here are many ALS, and I suggest row, column and box ALS on separate slides.  Then on separate and split windows, you can search for restricted commons and toxic sets.

When an ALS contains all candidates for a number that lie within its containing unit, that number cannot be removed from the ALS. Call it a stuck number.  Now when one of the    n – 1 remaining numbers is removed, the remaining numbers join the stuck number become a locked set.  The only effect of the stuck number is to expand the ALS to another cell.

There are many stuck number ALS in Unsolvable 40. Include them in your enumeration and toxic set search.  I’ll checkpoint that in the next post.

About Sudent

My real name is John Welch. I'm a happily married, retired professor (computer engineering), timeshare traveling, marathon running father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. The blog is about Sudoku solving. It covers how to start, basic solving to find candidates efficiently, and advanced solving methods in an efficient order of battle. It is about human solving methods, not computer solving.
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1 Response to Advancing to LPO on Unsolvable 40

  1. I’ve found your article on my iphone and i wanna say thanks for it! It’s a nice www you have over here! I’ll visit it more in the future! Thanks, Frank

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