Bookends of the Only Hard

This post checkpoints the only sysudokie bypass casualty and the only sysudokie basic survivor, in this second review of Manuel Castillo’s Only Hard Sudoku collection. The report of my first review was posted 1 ½ years ago, March 29, 2016. That review used every 40th puzzle, instead of every 42nd, and had almost identical overall results. I was using the bypass then, but not the 3-fill. The overall results of the two reviews are consistent, with the 3-fill tending increase the length of effect lists in the basic trace.

Looking back, I can see an abundance of 3-fills in the bypass trace of Only Hard 254.

If that doesn’t describe your version, and you’d like a close look at the 3-fill, load up a grid and read the trace, noting the reason for each move.

Here’s the line marked grid for Only Hard 338.






And the basic trace:

Now prevention of each of the two available rectangles requires promotion of an extra candidate, and the removal of its slink partner. The removals are decisive.

The conclusion of both reviews is that the Only Hard collection is primarily basic level, with a wide range of collapse points.  The Castillo Only Extreme’s wait in ambush.

 Next post was intended to be Manuel’s Only Extreme 46, the second Sudoku of our Only Extreme review, but two more timely subjects have intervened.

First, the Dave Green Sunday 5-star of September 3, 2017 at right made a PR jump into advanced territory, and then was caught with multiple solutions. That’s next week. This is your chance to uncover multiple solutions yourself without a computer solver.  See the Multiples section of the updated Titles page (menu bar) for a list of post examples, by coloring trials.



Secondly, frequent contributor Gordon Fick sent me a better response to the imbalance of Only Extreme 3 which makes the cluster expanding not-both trials avoidable, and snatches back 3’s EXTREME badge as we start the review.

I’ll be posting my effort on Only Extreme 46 at left, on October 10.



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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