Beware 175 Follows Suit

This continues the review of Will Shortz’ Hard Sudoku v.1, with another documented basic finish. Starting the Guide?  Accounting for each move in this series, then trying them beforehand, will make Sysudoku basic yours.

Beware 175 matches 165’s collapse point, but with slightly different triggers, a boxline and a naked pair.








The box/line interaction, or boxline, occurs when marking line r5. No 9 candidate appears in r5 outside the East box, so the true 9 is in r5. The other E9 hopefuls must clean out their desks, and leave the building.





The naked pair begins the collapse.










Next week, its Beware 185.  The Hard Sudoku v.1 review ends with 195, then my plan is return to earlier reviews to update all review posts to Guide methods and drawing conventions, with weekly post reporting on changes. The earlier posts will remain accessible through Title and Find It pages, and the monthly archive pages. New collection reviews can be undertaken on reader request.

The first review update is half done. It is the KrazyDad Insane collection, beginning mid July 1013.

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A Hidden Single Dispatches Beware 165

This post continues a review of Will Shortz’ Hard Sudoku, v.1. with the sixth of ten pre-selected puzzles. Each one is resolved at the basic level. The detailed review requires time and patience,   but its value is the detailed examples of Sysudoku Basic, an entertaining and efficient way to prepare the grid for advanced  methods. The starting point for reading this blog is the Guide, a network of pages accessed from the menu bar above.

A tough line marking of Will Shortz’ Hard Sudoku v.1 Beware 16 ends with a hidden single.










Here’s the grid at the hidden single SWhs4. In row 7, with six cells unclaimed, only one is available for 4.







Next is Beware! Very Challenging 175.

You also might enjoy following the update posts reviewing Krazy Dad’s Insane collection, beginning in July 16, 2013. It’s the beginning of an effort to update earlier post examples based on what I think I’ve learned since.

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Be Especially Aware 155

This post demonstrates how, in line marking, the partially line marked grid invites the error of using  an incompletely marked cell as a completely marked one.

Every Beware in this review of Will Shortz’ Hard Sudoku v.1 highlights a different basic challenge. This illustrates why treating the basic stage seriously is a source of enjoyment not to be missed.

In Beware 155 most placements occur on a grid with five marked and four unmarked lines in each direction. Here is the grid as a long collapse begins with a hidden single N7 in c6.

In conventional basic, we would finish the line marking before seeking clues.


But its Sysudoku Basic, which continues from N5 as reported in this basic trace.

Now let’s examine the grid where the c6 naked pair 69 confirms N8.  It does because c6 is line marked and we know the entire contents of r3c6.  Looking over at r3c1, we might think we have a clue 8r2c2. But we don’t, because c1 is not marked, and we don’t know there is not an 8 candidate in r2c1.


We are not digital computers.  Such a mistake is based on the type of assumption our brain makes every waking moment, just to navigate our clamorous world. The fill strings along the edges are a record of what is line marked and what is not. As we line mark, we must stay aware of the fill string record.

Moving down the trace a little further, we reach the point where the contents of r3c5 is settled, and the hidden single C8 can be declared.

But we trace it as c5hs8 because column 5 is the unit in which the value 8 has only one place.

Beware 155 is solved without marking another line via fill string.

Next  comes Beware! Very Challenging 165 in the Will Shortz Hard Sudoku v1 review.  Yes, another challenge of your line marking concentration. Or, if you’re a skeptic, try it your way and compare, with data.

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It’s the Bypass In Hard Sudoku v1 145

I had Will Shortz’Hard Sudoku v.1 145 collapsing in box marking, showing that every phase of Sysudoku Basic is actively solving, not just accumulating candidates for advanced methods later. But in process of writing this up, I discovered that the bypass had found a way to keep its collapse going.

Here is the basic trace.

I had missed that the chute 3-fill Cr4[158] leaves the c4 naked pair 69, that also completes the r8 naked pair 69, that gives SW8 and two more clues in the SW box.

It works, because subset pencil marks are posted in the slink marking bypass.



Next,  the review continues with Hard Sudoku v1  155.

On the advanced front, the review of KrazyDad’s Insane collection is being updated, for pattern analysis examples in the Guide. So far updates of July 2013 on Insane 415 and 425 are posted.

The AIC Hinges page of the Guide is being revised to include the AIC boomerang, a type of elimination ANL with its own spotting technique.

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Three Basic Phases on Beware 135

An easy basic workout, with help from 3-fills, a hidden single, many naked pairs, and a hidden dublex in Beware 135, the fourth in the review of Will Shortz’ Hard Sudoku, v.1. And two suggestions for Sysudoku readers.

The basic trace shows a collapse in early line marking.

Immediate effects are indented under causes.

3-forms are signaled first by the unit names and square bracketed lists of values.

Line pairs and other line subsets are denoted by ‘s’ and a list of values.

The grid after the bypass shows the fill strings for claimed chutes. Row 6 has one string for the chute and one for the remaining 3-fill.







Chutes are marked in box marking. Corner and side placement of pencil marks signals strong links (slinks) and aligned (chute) triples. Box slinks on top corners, row slinks bottom left, column slinks bottom right.  Middle bottom marks for row chutes and middle right side for column chutes.


So far this isn’t done elsewhere.  Most Sudoku experts aren’t into human engineering as yet. Encourage them.

Here is the line marked grid, at the hidden single 9 in the East box.  Bi-value cells (bv) are outlined in green. Candidates in marked lines that are not slink partners are in a list starting on the middle left side of the cell.

We don’t add these candidates to the grid until they are needed. The fill string process is simple and efficient.

That’s more human engineering rarely suggested elsewhere. Proven since 2011. Tell your favorite Sudoku guru it’s about time.

Next is Beware! Very Challenging 145. Like the other 9 in the Hard Sudoku, v1. review, it will not spoil your weekend.

For its examples in support of the Guide’s pattern analysis, the Krazy Dad’s Insane collection will be the  first past review to be updated to current Sysudoku conventions.  This collection is among the hardest I have reviewed, and a favorite.

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Hard Beware 125 Bypass

This post continues the review of 10 pre-selected Beware! Very Challenging puzzles from Will Shortz’ volume 1 of Hard Sudoku, with Beware 125. The review is a Sysudoku Basic Clinic, all being solved before candidates are completed and advanced methods begin.

The basic trace is one long bypass collapse, requiring a restart at the left to stay on the screen.

After that first leg down to S6, we see a characteristic of this collection, a large number of naked pairs, some claiming box space to create others.

The first one, SE56, is easy to miss. The steep run from there demonstrates sharp bypass action and 3-fill power.

A chain of pair resolutions comes at the end.

Our next Basic challenge is Beware 135. It is another chute filler, requiring accurate box and line marking.

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Chute Filling Beware 115

The second selection for the review of Will Shortz’ Hard Sudoku v.1 is Beware! Very Challenging 115. After a checkpoint on the Sysudoku Basic solution path, there is a brief report on the Guide’s Pattern Analysis page, now published in part

Hopefully, you are using this series for Sysudoku Basic practice, and have already spotted a distinguishing feature, the 3-fill claiming of a chute by slinks and aligned triples, implying further fills and clues in the box. For new readers, my “chute” is the row/column intersection of three cells.

This type of 3-fill is frequent in the bypass. In the diagram of the completed bypass, how did the 6 digit fill string on c4 get there?

The claim on c5 for 1,2 and 6 is obvious, and it implies that Sc4 must contain 7, 8 and 9, which claims a 3-fill on c4 for 126. That last claim may have produced a naked pair and clue for the diagram, to raise some eyebrows.

All of that is well documented in the bypass trace, with the help of the explicit 3-fill brackets added to Sysudoku Basic last year. Here is the bypass trace getting us to the diagram above.

There are ten 3-fills in the bypass, marked by the square brackets.

Box marking fills in the claims and mental slinks.

Line marking a column creates a hidden single on a row.

Here’s the grid at the point of collapse. The hidden single occurs in r8 as the naked pair in c8 removes the only other 1 in r8.







The collapse includes another chute fill, as 8 marks claim the third cell in SEc7 to force 3r9c9.


Next we take up Hard Beware 125 from Will Shortz’ Hard Sudoku v.1.  It’s a natural for coloring, but here we want to know if it survives Sudoku Basic. Have your rating ready.

Meanwhile, part of the Guide page on pattern analysis is up. It is about tools for analysis, freeforms and lettering, and fundamentals of applying them to X-Panel Pattern Analysis (XPA) and Limited Pattern Overlay (LPO). The remainder of the page, to be added soon, combines patterns and coloring.

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