Beware 185 Finished in Line Marking

A basic clinic is concluding  for those wishing to make assembling candidates an entertaining task. It is Sysudoku basic on Will Shortz’ Hard Sudoku v.1.  The solution detailed this week is Beware! Very Challenging 185.

Here is the basic trace to within a few obvious moves of the solution.

The bypass grid shows what clues and closed subsets of candidates can be identified before any other candidates are sought.







The box marked grid shows the strongly linked pairs of candidates, the ones most affecting  the placement of clues and other candidates.

Beware 185 is solved after five lines are marked. The challenge for all of these puzzles is in the bypass.



Beyond that, there’s nothing hard about Hard Sudoku v.1.

The solution of one last Hard Sudoku review puzzle, Beware 195, will be traced out next week. Try for a bypass solution.

The next post also begins a series of posts reporting on update results on earlier reviews. It is time to apply seven years of Sudoku experience to the whole blog. The series begins with KrazyDad Insane collection. Six of the review puzzles have now been updated, the entire series running from 7/16/2013 to 9/10/2012. It’s easy to pull them up with the monthly archive list to your right.


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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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