Pattern Trials Peel the UHC 487 Onion

The ultrahardcore review ends, with Stefan Heine’s 487 giving up a naked single and two skyscrapers, and a jaw dropping complex 1-way, shuts down the solver team. Slicing at it with three onion peeling pattern trials leaves very little for the team to chew on. The post ends with a few words on how the  2021 Sysudoku blog will be a little different.

In line marking UHC 487, r6 gives you a naked single W7, free of charge.

Then in r1, there it is, another skyscraper in the 2’s. This time, the ANL victims are slink partners. We get two clues, and we don’t need to leave the chain behind.

But that’s not all. The S2 clue leaves a 6-slink in r9 that matches a slink partner in r7. This skyscraper we leave on for another victim in r4.

After this promising start, my solver team gets nothing, except a truly impossible Beeby complex 1-way for one more removal, plus a SEc8 boxline removal.

Readers who despair over my diagrams should see the corresponding Beeby chain notation below.

The special characters mark the departure of winks to erase an interfering candidate. The symbol repeats at the slink created by the erasure. These erasures are valid only in the chosen direction of the chain.

To avoid unnecessary notation reading headaches, ignore the special characters at first, simply accepting the (=) slinks. Then draw the branches from the character marked candidate whose erasure enables the slink started at the second symbol.

On the 6-panel, there are only two South to North freeforms containing 6r9c1. Starting the trial on the first 5 of 7 candidates, the trial itself will probably select the right path, if there is one. If not, then the failure confirms 6r9c8 as a clue, removing it from the 6-panel.

The trace is long, but there is a steep collapse to a contradiction as two 3’s are forced inton c7. The clue and two removals do not wake up the solvers.

Next I look at other edges. From East to West, there is only one pattern containing 6r3c9. If the freeform fails, 6r4c7 is an orphan as well, because c9 must be included.

Again this test of 6 candidates fails quickly.

Now we have two sets of East to West freeforms, three from r4c9 and and two from r6c9. The red one fails to reach c1.

In a trial of patterns containing r4c9, an initial coloring yields two traps.


gets to a 497-wing

followed by an XY ANL

and a green wrap.

So what pattern was the true one? Now we know.

That winds up our review of Stefan Heine’s ultrahardcore right page collection. Let’s keep trying for ‘no trial’ humanly practical solutions to these gems.

So what happens now?

There being no urgent reader requests for another collection review, early 2021 posts will be about  expansions and revisions of The Guide, that link on the bar menu. You will be in on explorations, independent of a review schedule, of current and prospective Sysudoku Guide topics, prior to its publication in book formats.

Posts will continue to be weekly, Tuesday noon EST, but I expect the blog will be much more amenable to meaty comments and very careful replies. As many readers know, I keep comments of interest only to myself to myself.  Comment about your ideas. Put them on a post or a page.

The first 2021 Guide topic is lite coloring, to my knowledge, an invention of reader Dov Mittelman.  

 Thanks to an alert from another expert friend Gordon Fick, here’s a puzzle recently highlighted on the EnjoySudoku forum that provides an excellent example, when you overlook the hidden quad that destroys it. Next week, you’ll get my definition of lite coloring. If you’re into Sudoku Basic, try to corral three X-wings in line marking, then the quad. The puzzle is attributed to “Red”, a.k.a. Ed Russell, an early regular forum contributor. The forum offers “Pattern Game” solutions for the Ed Russell special, which could be one of those Guide topics later.

About Sudent

I'm John Welch, a retired engineering professor, father of 3 wonderful daughters and granddad to 7 fabulous grandchildren. Sudoku analysis and illustration is a great hobby and a healthy mental challenge.
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