A Very Hard Finale with Ardv2 398


A hard basic leaves it to an unusual ALS to shake things loose, enabling an XY and a UR to wrap it up.  Maybe the hardest of the pre-selected Very Hard.

 

Line marking looks easy, until you look at the completed grid.

 

 

 

 

 

 

 

Fortunately, and ALS-XZ comes to the rescue.  With 9’s in common, one ALS has the true 9, and the other, the true 6, and 6r7c7 sees all 6’s in both ALS. The 5 clue removes 5r1c7, leaving a 146 naked triple in r1.

There the action stops.

 

 

 

 

 

Turning to coloring,  a second cluster fails to produce a bridge. Doubling back to update the bv map, I realize that the 5 clue’s removal of 5r7c8 creates a decisive XY along the altered railway. The removal wraps tan and confirms yellow. Yellow wraps orange, and its yellow and red.

 

 

Yellow also sets up a productive UR, Type 2, removing a bunch of 6’s.  The resulting E1 clue confirms blue, and there’s nothing left to say, except that Ardv2 398 was exceptional in its display of advanced methods.

Next post concludes the Ardson Very Hard v.2 review with a redo of the corrected Ardv2 38. Just in time for the 4th.

But more fireworks come a week after. The side issue about multiple solution puzzles, brought on by my loading typo on 38, and prolonged by a missed pencil mark, is taken up again in the next post. 

 

 

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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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