Wex 429 is Sued

In the review of a sequence of 10 Weekly Extreme Competition puzzles, Wex 429 is toppled by an easily verified Sue de Coq. The post begins with a checkpoint for the reader’s own solution of Wex 428 by single alternate Sue de Coq.

wex 428 sdc 2After line marking of Wex 428, the contents of chute SE r8 is described by

SEr8 =3(1+9)(4+7) +437

If alternate (1+9) is not missing, the verified Sue de Coq will remove 9r7c8, leaving SE5.

The wink and arrows show how SEr8 = 437 confirms two 9’s in c4, verifying the Sue de Coq.   The inference path comes directly from the trial trace

wex 428 sdc2 trThe marking following up SE5, remarkably, uncovers the same naked triple we saw in the last post,but with a different result. When it is finished, there is a field of 4789 candidates with XYZ –wings waiting to be found.


wex 428  XYZ skyscraperI looked no further when the XYZ map revealed this 189 wing. The victim “sees” the third 9 of the toxic set via a forcing chain. But hanging on the outline of the forcing chain is a 9-chain almost nice loop. The wing and the ANL are interlocked, in that the removal generated by each destroys the other.

Did you find this one? If so, are you worried that neither method works because a component candidate is lost? Believe me, it’s OK. The field of candidates left you after correct solving operations supports either removal individually. You’ve been using false candidates to help remove other candidates all along.

Anyway, the collapse of 428 is immediate. Weekly Extreme vs single alternate Sue de Coq is a rout so far.

Wait, wasn’t this post about Wex 429?

wex 429 bypass gridA generous slink marking bypass leaves very little box marking:

The bypass, which I came to only recently, is almost free of pencil marks. The exception is the marking of subsets. Free cells are clearly marked. It is my favorite phase of basic solving, and I try to go as far as possible with it, before box marking, which adds strong links (slinks) defined by units.

Are you still finding all candidates first? If so, stop. Life is too short.

wex 429 bypass trThe bypass trace follows the same sequencing as box marking, but is not separated into numbered lists. It is box marking, with slinks followed to their conclusions. Writing them in pencil marks is bypassed, except for naked subsets.

wex 429 bm trBox marking of Wex 429 is very short. Numbers are omitted when all 9 clues are in place. No marks were found for 2, 3 and 6.

wex 429 lm swordHere is line marking in progress, showing a swordfish found on rows that have been marked. The “fish” are left in place to prevent 5-candidates being added to prohibited columns as the remaining rows are marked.

The lists to the right and along the bottom are fill strings, giving the numbers eligible to fill that line. The line marking process is much more efficient than going over every cell scanning through all numbers to identify fill candidates.

Lines are processed, fewest free cells first. After all rows or all columns are marked, the remaining lines in the other direction are “closed” by marking line slinks and X-wings. Line slink marking makes it easy to spot x-wings in line, but I don’t try for higher order regular fish. They’re much easier found on the X-panel.

wex 429 sdcThe first Sysudoku action upon completing the candidate field is to exploit the grid’s bi-value cells. In sysudokie speak, it’s the bv scan.

The grid is inspected, chute for chute, for Sue de Coq, Aligned Pair Elimination (APE), and unique rectangles. APE generally require more bv, so SdC are more frequent. This SdC is hit near the end of the grid scan. The chute contains

SWc3 = 7(3+5)(2+6) +537.

The SdC is verified by the diagram below, and has two victims.

wex 429 verifiedThe resulting removals trigger an immediate collapse of 429, traced below for the record.

wex 429 final tr

I don’t think Sue is perturbed at WEC for any reason, but the Sysudoku single alternate Sue de Coq  is bringing the “Extreme” label into question here.

Maybe the come back will be strong, and will start with 430. We’ll find out next week.


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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