Fleshing Out Stuart’s ALS Node Figure 30.1

Andrew Stuart’s The Logic of Sudoku, in a chapter on Almost Locked Sets, presents an example of an ALS node in a confirming Almost Nice Loop, as Figure 30.1. This post fills in the solution, before and after the series of four grids in the AIC Hinges page of the Sysudoku Guide, that illustrate the flexibility of the ALS node in AIC.

As is the case throughout The Logic of Sudoku,  solving to Figure 30.1 starts with candidates  scanned directly from the given clues. Sysudoku Basic usually gets to advanced in a more entertaining way, and with more information.

When basic uncovers no clues, as in this case, there’s as many candidates.

Needing to account for a few candidates missing, and I went through the bv scan with the same level of success: none.

But next, on the 1-panel, a finned swordfish succeeded. The three kraken victims escaped.

Then on the 4-panel, a skyscraper triggered a Nc6 boxline, accounting for the remaining missing candidates in Figure 30.1.





Getting to the 8-panel, there is a kraken 8-wing and a Cc4 boxline. These removals come before the AIC scan in Sysudoku, but  do not affect Andrew’s example.

X-chains and fish are best at cutting through sucn a sea of candidates, and the same disconnected bv field that frustrated the bv scan makes coloring ineffective.

So it’s time to add the hinges and search out some AIC. For the results, go to

Guide/Sysudoku Advanced/AIC Hinges, where, under the heading The ALS node, the page continues with Figure 30.1 and two more grids, in which the innocent looking r12c3 ALS 245 is wired to produce a  confirming ANL, a grouped elimination ANL, and a nice loop.

Coming back from  that display, one AIC hinge gets the last laugh, as one of the winks makes the decisive elimination.  This type of ANL, with the victim seeing a toxic set member with a hinge wink,  deserves a distinct name,

and I propose the “hinged ANL”.

The hinged ANL is generated naturally in the effort to keep a hinge initiated chain going until something happens.

After working through the puzzle of Andrew’s ALS node example, I was hoping for another one in his immediately following challenge puzzle 17.  Next post is a report on that one, in which I got more than enough challenge. If you want to get your discoveries before reading about them, here’s Logic 17.

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Funster Extreme 130 Falls in Line Marking

The funster Extreme collection review closes here, with the early departure of the last pre-selected puzzle, Extreme 130. Charles Timmerman’s funster Hard to Extreme Sudoku includes 134 Hard, 134 Very Hard and 134 Extreme puzzles.

Here is the Sysudoku review table for the funster Extreme collection. Every 14th puzzle was taken, arriving at 130 to finish.

Maybe 130 pulled strings to get a seat in the Extreme gallery. The collection exhibits pleasing variety of advanced methods, and plenty of highlights. These include a finned X-wing in line marking, some Sysudoku firsts in coloring, and several elimination victims by inference chain “seeing”.  I rate it “funster Advanced”, but not extreme. An appropriate level for funstering.

Not much left to do,  but display a basic trace of Extreme 130. Two naked singles on the same line trigger a quick collapse.

Next, and before starting the basic level review of Will Shortz’s Hard Sudoku, v. 1, is a report in two posts on my experiences in a return to Andrew Stuart’s treatment of the ALS node in AIC chains, in The Logic of Sudoku. I followed up his Figure 30.1 example by working the puzzle from the beginning.  The result is the more comprehensive view of the ALS node now in the Guide, as signaled by AIC hinges, and as it is re-used twice for further eliminations.

In case you would like to compare details as usual, and without looking at the first ALS node in Logic’s Figure 30.1, here’s the given grid.

In search of another example, I also worked through Andrew’s challenge puzzle 17 immediately following  Figure 30.1. It provided another ALS node example, but further insight into AIC hinges, for the Guide.


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A funster Extreme 116 Labor Day Special

An effective bypass, and a simple uniqueness rectangle, and three choices to close down funster Extreme 116 early. Charles Timmerman’s funster Extreme collection is less than  extreme, but a good introduction to advanced solving methods.

The basic work is easy, because the bypass does most of the heavy lifting.






Advanced 116 begins with a Type 1 unique rectangle.  Candidate 1r6c8 is required to prevent an obvious multiple solution. The two candidates seeing it must go.






After a follow up of


there is a choice of three triggers for the collapse:

You have a border hugging XY nice loop.










Or a deceptively decisive Almost Nice Loop.







Or, if you’re a snapshot collector, or always do XYZ wings first, a regular 489-wing with a far seeing victim.








Our final funster selected for the review is Extreme 130. Review table next tim. The next review collection is Will Shortz’s Hard Sudoku, v. 1. Find the previous Shortz collection reviews on the Titles page. The latest new Guide page is about AIC Hinges, a topic way beyond Shortz.


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Funster Extreme 102 Goes BOGO

Barely escaping the bypass, funster Extreme 102 offers a thematic example as inference chain seeing nets an extra victim for the collapse.

Close to a bypass victim, Extreme 102 finishes basic quietly.

On the line marked grid grid is a flashing sign, a a four cell remote pair chain. Actually, there is a a second one, but this this one has a victim. Well Actually, this one has a second victim, courtesy of a skyscraper 1-chain.

Well, actually, the X-chain can be replaced by a naked pair necklace. The victim sees one terminal directly and the other, by the r6np13  wink. The two removals collapse what’s left of funster Extreme 102.

The bypass and AIC wink clinic continues next week with funster Extreme 116.


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A Timely Finned Fish in funster Extreme 88

Continuing the review of Charles Timmerman’s funster Hard to Extreme Sudoku, with Extreme 88.

The basic compensates for a modest  bypass with a favorable line marking. A naked single early and a finned 2-wing late. Finned fish is a topic recently added to the Sysudoku Guide.

The finned X-wing is ordinarily spotted on the X-panel, but looking up from the 2-slink on r8, the presence of the victim in the box of the fin jumps out at you.





Following the regular order is a regular 237-wing.



After the follow up,

I try to enlist the naked pairs in coloring.

The cluster expands by trapping 2r2c8, and blue is wrapped in r5. Game over.









Next is Funster Extreme 102 which illustrates a Sysudoku theme in an unusual way.

Also, a Guide page on Coloring Fundamentals is now available, off of the Sudoku Advanced page

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Funster Extreme 60 and 74 Go Together

Two brief advanced appearances are reported in this post in review of the Extreme section of Charles Timmerman’s Funster Hard to Extreme Sudoku.

In Extreme 60, the bypass starts with a 3-fill and uses them to solve a big wedge. The remaining line slink marking is easy.


The rest is easy too.  A type 1 unique rectangle is enough for a collapse.






In funster Extreme 74, a less decisive bypass, . . .

. . . is aided by a 6-wing, a form of fish directly signaled by line marking. Regular fish of all sizes are now explained in the Guide as  X-panel  methods, but the X-wing is often spotted in line marking as an alignment of slink marks.

This fish has no victims now, but the fish icons are left in, to exclude 6 candidates from r46c3 and r4c7 in the remaining line marking.







As basic is completed,  this XY-wing and naked pair triggers a collapse









Next in the review is Charles Timmerman’s funster Extreme 88. Next in the Guide is Coloring.


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Funster Extreme 46 Not So Much

The review of Charles Timmerman’s funster Hard to Extreme Sudoku continues with Extreme 46. It’s  entertainingly advanced.

Extreme 46 has its moments.  The basic trace is spread across the page with 3-fill after 3-fill. Two unusual events occur in box marking: three clues after the bypass, and the N 5-slink claim.

Here is the naked triple in c4.










Right out of line marking, a testimony to construction fun versus anxiety inducing search, a Rube Goldberg 275-wing. The grouped 7-chain wink places the third member of the toxic set out of sight of any victim, but hey, it’s an ANL. Celebrate.


On down the XYZ map, a regular 471-wing with an irregular victim. 1r3c1 sees the third toxic 1 via 1-chain.









That removal enables one of those long, rambling XY nice loops through the bv patch. The many victims include the single triumph of the Rube Goldberg 275-wing, but we don’t mind.






The follow up includes a shift of the nice loop to make another removal. The resulting naked pair grows the bv patch.







When I catch my breath and apply the crayons, blue is wrapped in c2, and the green army marches in.

Next time, we do funster Extreme 60 and 74. If you’re playing along, its mostly about comparing basics. The starting grids are below, 60 left and 74  right.

A new page on finned fish is up in the Guide.


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