Super Fiendish Ends With 87 and 97

The review of Brian Challenger’s Sudoku Super Fiendish is ending quietly. SF 87 gets into beginning advanced, while SF 97 is finished in line marking. As to difficulty level, this small collection ranges widely and erratically. Is it  Fiendish? Not really. It visits advanced regularly, besting Wayne Gould’s Train Your Brain Su Doku. But not reaching AIC building, it is nothing approaching super fiendish. By contrast, the Nakamoto “Extreme” collection coming up next is much more deserving of such a title.

The Super Fiendish review table:

Super Fiendish 87 distributes basic placements over the three Basic stages:

One advanced move, a unique rectangle type 1, is enough.

Any candidate 6 seeing 6r5c2 must go, since that 6 must stay until the deadly 12 rectangle is otherwise destroyed.

As it turns out, these removals generate four new clues and the collapse of SF 87.








On Super Fiendish 97, nothing breaks loose until c1, the ninth line of line marking.

Going back to the first hidden single on r6, the line marking left 18 in r9c6, which is taken as  hidden single because the r6c6 is the only cell in r6 available for 1.

Note that r6 is a 4-fill where 1 is visible from three cells. The hidden single could have been called in the bypass at W3! And also by definition, every single or pair from a resolved 3-fill could be termed “hidden”.

Here’s the solution of Super Fiendish 97.

Next week, we embark on more ambitious review project at the expressed invitation of J.B. Nakamoto in the forward pages of his or her Sudoku Puzzle Book, Extreme Level, described on the front cover as “Diabolically Difficult Puzzles for Advanced Solvers”. The 10 puzzles pre-selected for the review are 3, 23, 43, 63, . . . , 183. Nakex 3 is below.


In this review Andrew Stuart’s SudokuWiki solver backs up the Sysudoku path through advanced methods and AIC building. As usual, the posts will provide interpretations, traces, grids and alternative paths consistent with the Sysudoku Guide.

The collaboration produces an array of examples in a completely documented context that is the best so far at illustrating the advantages of Systematic Sudoku.




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Super Fiendish Bookends 67 and 77

This post steps through the most fiendish of the 10 puzzles preselected for the review of Brian Challenger’s Super Fiendish Sudoku, SF 67. , and then adds one of the bypass victims, SF 77.

Looking at the trace, you might think basic is easy,



but the long fill strings reveal a tough line marking.

Advanced solving starts with hidden unique rectangles of type 2b. The floor to ceiling slinks project a victim clue into a reversible rectangle of four clues.

Then, after an X-chain ANL,







a regular 127-wing is extended into an inference chaining i127-wing.



The midfield action continues with a 4-BARN (Bent Almost Restricted 4-Set),


and an ungainly looking APE in which  5r4c9 cannot be combined with 1, 2 or 7 in r4c8 within sight of ALS 157 and ALS 2457.

The APE removal is telling,

leading to an XY railway of interconnected nice loops.




No removals result, but a nice loop generated cluster is expanded by a trap and wraps blue in r2 and c4, for the collapse of Super Fiendish 67.

In his comment to this post, forum member strmckr provided this quick resolution to SF 67 immediately after line marking. He terms it an ALS W-wing.

The restricted common is a forcing chain. Since one ALS will lose it’s 9’s. Any candidate seeing all of any other value in both ALS must see a true value. 1r1c9 does just that, and the removal collapses SF 67. With all the ALS in every grid, can you hope to spot such an event? Not really, but you can see the appeal of writing code that can find every instance of it.





Super Fiendish 77 might have presented similar advanced challenges, but was too vulnerable to Sysudoku Basic. It takes a while but the collapse is relentless.












Next week,  the Super Fiendish review ends with 87 and 97. For the next review, get a copy of J.B. Nakamoto’s Sudoku Puzzle Book, Extreme Level.

The 67 and 77 solutions:


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Wayne Gould and Super Fiendish 4-57

This post reports two puzzles in the review of Brian Challenger’s Super Fiendish Sudoku, Sufi 47 and 57. Both are basic level, and in fact, half of the review puzzles are. For Sysudoku solvers, the term ‘fiendish’ is an overreach.

The only other ‘fiendish’ collection reviewed here is Wayne Gould’s Train Your Brain Su Doku Fiendish, published in 2008, and taken from the New York Post. It was briefly reviewed in November 2014.  “Fiendish” was a cover label on Gould’s New Your Post collection, but  all review puzzles from that collection were basic level. To his credit, Gould advocated Sudoku as mental calisthenics. He was aligned with the Sysudoku slink marking bypass in his advice to minimize pencil marks.

Here is the line marked grid of Sufi 47 at the first naked single of line marking, as the collapse is getting underway.




The naked single SEns1 appears in the slink marking of c9 in the basic trace below.


Super Fiendish 57 has a very similar basic trace, and again, a collapse in line marking triggered by a newly naked single SWns9 on r7.




The sufi 57 basic trace:

Next are sufi 67 and 77. One is a bypass victim, the other, the most advanced of the reviewed Super Fiendish. Here are the solutions of

47:                                                                        and          57:



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A Coloring Tidal Wave Drowns Sufi 37

Here, Brian Challenger’s Super Fiendish 37 makes it to advanced, but with the bi-value field   inviting multi-cluster coloring, a systematically easy solving technique. There are some X-panel fruits to harvest first in the order of battle, before coloring closes the book with a snap.

A Sysudoku review reports how puzzles behave in Basic, the gathering of clues and strong links. In this case, there was some thinning of the candidate cloud in the bypass, and a large contingent of box slinks preceding a naked triple closing line marking.


Here is the line filled grid with fill strings attached.  The naked triple adds two bv.

Some bv are due to local shortages of cells for unplaced candidates. Bi-value cells are the grey areas corresponding to the black and white of clues.


From the bv scan, the first sufi advanced move is this hidden unique rectangle, type 1.  If 3r5c8 is true, then 7 is forced in adjacent corners. Values 3 and 7 can then be interchanged in the corners without affecting any cells outside the rectangle. That means that the whatever solution is derived can be duplicated with these interchanged values.

Next, from the X-panel, an 8-chain ANL brings another bv.










A tentative blue green cluster stalls, but finishing the X-panels brings a swordfish. There’s only one victim, but the removal gets a box/line removal and another bv.





The second, red/orange cluster is pervasive, and a collapse begins with coloring traps. 9r6c3, 4t7c8, 3r9c1 and 4r9c9 see both colors. Cell r9c1  declares that red and blue are not both true, which means that green or orange or both are.




The departures of 3r9c1 or 3r8c7 here merges blue with orange and red with green. And the 1r9c8 trap colors 1r9c3 orange, leaving red in command and wrapping blue in r9c1. Suddenly it’s over. Ever see a solution in color?




Next time, it’s Super Fiendish 47 and 57, both basic.




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Super Fiendish 17 and 27

Two of Brian Challenger’s Super Fiendish, 17 and 27, are put together because solution paths are short.

Stage right is the Sufi 17 line marked grid with an immediate, and decisive, XY nice loop.

The follow up features an early  naked triple c2nt234.





A basic trace that gets you to the grid above:






Now you’re prepared for a bypass finish in Super Fiendish 27:

Solutions:           17:                                                                                       27


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Brian Challenger’s Super Fiendish 7

The review of Challenger’s Super Fiendish collection opens with a long post, revisiting some advanced methods not seen here recently.

Somewhat fiendish is the stonewalling in basic. The bypass gets nowhere, and the hidden triple alone removes candidates.

Here is the hidden triple before removals on the line marked grid.








An XY wing brings a hidden single in c4.








Next is this finned 4-wing removing 4r7c3 that sees fin 4r8c2 in fin box SW.

Alternatively on the X-panel, the same candidates form a 4-chain confirming ANL generating the same effects.





The removal enables a second XY ANL, a 598-wing, that generates an r6s17 naked pair.






The pair has dramatic effects, including a long time not seen favorite of mine, the Sue de Coq below.



A description of the contents of intersect SWc1, based on the SW remainder ALS 589 and 24, is

SWc1 =


In the c1 remainder, 8 or 9 must come from cell r5c1, and the other 8 must be discarded. The ALS 247 provides a complementing 2 or 4. Besides the c3 naked triple 124,

a third XY wing  provides the trigger for the remaining collapse.


Brian Challenger does not provide answers in Sudoku Super Fiendish. That’s a break with tradition, and an inconvenience for sysudokies who trace their solutions. A trace shows you exactly where you departed from the solution. Solutions are provided here for the review puzzles. Here is the SF 7 solution. Hopefully, you could ignore it.

Next post reports on 17 and 27. One falls in the bypass. Find out which before next Tuesday. No previews on Challenger’s Super Fiendish, remember?





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Metcalf’s Second Patterns Game Entry

This post reports a Sysudoku solution path for Mike’s second Patterns Game entry on a extraordinary pattern of givens. As a successful entry, I believe it had to meet the contest requirement for a simpler solution than is found here. Maybe a reader can show us one.

In that bypass challenge offered last post, how far did your bypass go in the box marking below without writing down any of the unpaired box slinks? It doesn’t really matter, but it’s fun.

Here is the box marked grid, for comparison to yours.  Uncertainty persists in three corner boxes.

Now when line marking fills out the candidate grid, you’ll see how you might slug it out with the patterns game referee.


On the line marked grid, with necessary fill strings, the first advanced moves are two hidden unique rectangles of Type 1.

Hidden UR’s are not what anyone has in mind for “singles”. There must be something else here that does not depend on them.








The  8r1c9 hidden UR removal enables a Sysudoku favorite, a BARN, a Bent Almost Restricted n-set. One value group, the only bent one, is toxic. Not a “singles” move.

The next move comes from the more advanced and laborious search described in the Sysudoku Guide as AIC Building. In AIC Building, you try to keep going any AIC slinking from any cell by any AIC means, until it reaches another candidate seeing its value in the starting cell. Expect it to take time and patience, although each AIC fun to build. Just have multiple copies of the grid to scratch up, or like me, just make many ©PowerPoint screen copies of the grid.

There’s at least one decisive boomerang here. Starting with a 9-chain from the bv cell r3c6, a reversed bv in r5c6 continues the AIC as a grouped 8-chain to the XY node switch to the 1 seeing its match in the starting cell. The boomerang’s return creates an Almost Nice Loop. If the starting cell is a bv, it’s a confirming ANL, otherwise, an eliminating ANL.

There are a lot of starting cells and possible closings. I’m not venturing to say how many boomerangs are on this already simplified grid.

But AIC Building isn’t singles. The grouped AIC boomer is decisive, triggering a “singles” collapse.

We move on next week to Brian Challenger’s Super Fiendish 7. Did you get your copy yet?

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