Chute Filling Beware 115


The second selection for the review of Will Shortz’ Hard Sudoku v.1 is Beware! Very Challenging 115. After a checkpoint on the Sysudoku Basic solution path, there is a brief report on the Guide’s Pattern Analysis page, now published in part

Hopefully, you are using this series for Sysudoku Basic practice, and have already spotted a distinguishing feature, the 3-fill claiming of a chute by slinks and aligned triples, implying further fills and clues in the box. For new readers, my “chute” is the row/column intersection of three cells.

This type of 3-fill is frequent in the bypass. In the diagram of the completed bypass, how did the 6 digit fill string on c4 get there?

The claim on c5 for 1,2 and 6 is obvious, and it implies that Sc4 must contain 7, 8 and 9, which claims a 3-fill on c4 for 126. That last claim may have produced a naked pair and clue for the diagram, to raise some eyebrows.

All of that is well documented in the bypass trace, with the help of the explicit 3-fill brackets added to Sysudoku Basic last year. Here is the bypass trace getting us to the diagram above.

There are ten 3-fills in the bypass, marked by the square brackets.

Box marking fills in the claims and mental slinks.

Line marking a column creates a hidden single on a row.

Here’s the grid at the point of collapse. The hidden single occurs in r8 as the naked pair in c8 removes the only other 1 in r8.

 

 

 

 

 

 

The collapse includes another chute fill, as 8 marks claim the third cell in SEc7 to force 3r9c9.

 

Next we take up Hard Beware 125 from Will Shortz’ Hard Sudoku v.1.  It’s a natural for coloring, but here we want to know if it survives Sudoku Basic. Have your rating ready.

Meanwhile, part of the Guide page on pattern analysis is up. It is about tools for analysis, freeforms and lettering, and fundamentals of applying them to X-Panel Pattern Analysis (XPA) and Limited Pattern Overlay (LPO). The remainder of the page, to be added soon, combines patterns and coloring.

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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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