KrazyDad Super Tough Review

This is a sysudoku grading review of the Super Tough puzzles available on the KrazyDad website.

KrazyDad is the creation of the very creative Jim Bumgardner.  It offers for download a huge number of free Sudoku  puzzles at levels ranging from  Easy to Insane, along with a mind boggling array of other kinds of puzzles.  That’s The Super Toughs are almost Insane, being next to the highest level.  Let me just say I’m glad I started there.  If Jim likes what I’ve done here, and after I’ve posted a bit more Sudoku theory I have in mind, I just might go Insane.

My grading survey sample of 10 puzzles were the #5 puzzles from volume 5, books 1-10. There are eight puzzles in a book, and 100 books in volume 5, so my review sample is a systematically scattered smattering. The conventions of the review table below are explained on the review page.

Super Tough review

The KrazyDad survey Super Toughs graded widely across the advanced methods, from bv scan to advanced coloring.  The notable exception was the book 10 #5, which ran dry inbox marking at number 5, with only four numbers unassigned.

Super Tough starting clues are generous, and line marking tends to be easier than the Sheldon and Longo puzzles just reviewed.   A large bv field usually supports interesting bv scan activity.

The review sample brought some remarkable coincidences of XYZ wings, XY-chains and finned fish occurring  in pairs. There were also multiple techniques removing the same candidate and removing more than one candidate from the same cell. I’ll show these in my snapshots next post, but right now, let’s look into those alternative solutions of Super Tough v.5 b.1 #5.

Super Tough v5 b1 lmAs a checkpoint on line marking, here is the grid with my fill strings attached.

Did you find the UR?  I missed it at first and went on to coloring to encounter a very interesting color wrap.  I’m reporting that first, then the somewhat unlikely UR.


Super Tough 5 1 5 color 1My blue/green cluster  traps an indecisive 4-candidate, leaving a lot of uncovered bv toward the southwest.  The red/orange clashes with it in r9c9, and in the S box. The bridging logic is

r9c9 => !(green & red) => blue | orange

S=>!(blue&red)=> green|orange.


No candidates see the toxic sets, but

Super Tough 5 1 5 color 2orange & (blue | green) => orange  !!!

Orange =>(W5,W6=>C6m) and extends blue/green, forcing two blue 8’s in c7.

The green and orange candidates win.  Now repeat after me:

I believe in coloring .

I believe in coloring.

. . .


Super Tough v5 b1 URNow cranking it back to the line marked grid, here is the UR that would rob the diligent sysudokie of the coloring logic above.

A 3 or 4 in r3c4 forces the deadly rectangle, but neither does it alone, as the removal requires.  The branched forcing chain shows that   4 in r9c4 is capable of that feat.

The highlighted candidates are an equivalent form of marking I have used earlier in the blog.  I prefer the more explicit forcing chain.  This is also an example of Denis Berthier’s xynt-chain.

The UR removal is not enough.  We reach an impasse after

S5=>(SE5=>SW1=>SW4=>SW3, C5=>W6, W5, Sr8np23=>Sr7np48).

But the UR has enriched the bv network, and there is good reason to return to the updated bv map.  I think you should see both the XYZ map and the bv map at this point.

SupT v5 b1 bvxyz

In the XYZ map, the crossed out hinges mark the many “almost” XYZ-wings that were possible, but unfruitful.  My snapshots of the next post show many successful ones across the 10 survey puzzles.  On the bv map, the XY net is built on two main curves, red and black, plus purple and green extensions and connections.  The curves limit and organize the search, making long XY-chains easy to find.  An extreme solving method becomes merely an advanced one.  No big deal.

SupT v5 b1 URxycThe long XY ANL remove two candidates.  The 8 removal adds slinks, but the 6 removal does more.




The resulting naked pair in the N box triggers a raging epidemic through the bv:

SupT v5 b1 tr2The trace trails off where the remaining solution is evident, leaving a large stack of unexploited clues to the upper right, including a boxline marked at the outset.


SupT 5 8 5After  the upcoming Super Tough snapshots, we’ll conclude this KrazyDad review with a second puzzle, volume 5, book 8, number 5, the second from the review to reach the coloring level.  It has coloring logic I had no examples for, in  my coloring posts. If you would like to work through it with me, here is the starting grid.  I’ll have the box marking trace next post.

I’m looking forward to reviewing KrazyDad’s Insane collection.  I think you will too, after you see my Super Tough snapshots.  Don’t wait that long to download these collections.


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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