Wex 430 Bewitched by Sue de Coq


After putting up a decent fight in basic, Weekly Extreme 430 joins an embarrassingly long line of Weekly Extreme Competition puzzles defeated by the single alternate Sue de Coq, one my early advanced solving discoveries. This time it’s the verification of the second SdC that marks all the way to a solution.

wex 430 bm trBasic marking of Wex 430 was a challenge. Box marking wasn’t easy and left a fairly tough line marking.

On row 8, on the last row of 5 free cells, no 6’s were found outside of the South box, bringing a boxline removal.

wex 430 lm gridwex 430 sdc 1A single alternate Sue de Coq appears on r1:

NEr1 = 5(3+7)(1+9) will remove 7r1c3, if (3+7) is not missing.

 

But if (3+7) is missing, the naked pair 19 in the NE box requires a 1 or 9 from r1c3, removing the same 7r1c3. So it has to go, (3+7) is missing or not. We are led to look to see if the classic Sue de Coq created by the removal, removes anything else. But it does not, because the required ALS are not present in either remainder.

wex 430 sdc 2I scan top to bottom a row of boxes at a time, looking at row chutes, then column chutes, and trying to look for APE and UR rectangles at the same time.

My next encounter is another single alternate SdC,

Wc2 = 2(7+8)(3+9)+923 ,

the extra term occurring when (7+8) is missing.

 

I had to work hard on the verification, but I can’t complain. Turns out, it was the solution.

 

The trace was folded at  (C6, C1), to get it on the screen.

wex 430 final trHopefully we’ll break Sue’s witching spell with Weekly Extreme 431.

But next week, we take a short break on the Weekly Extreme review, to return to Antoine Alary’s “most difficult” of the 200 “toughest Sudoku puzzles known to man”. The reason is to help report an alternative solution by a Sysudoku reader, who took up the challenge and independently solved More Extreme 200 using his own order of battle. His comment appears in the More Extreme 200 post

You too can use comments on the Sysudoku blog to bring out alternative solving ideas. It doesn’t have to be a current post.  You don’t have to saddle yourself with the management of a blog to do it. If you like, I’ll gladly add highlight grids and traces, while giving full credit to your contribution, in a follow up post similar to the one you’ll see next week.

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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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