Another Dave Green Sysudoku Basic Workout

This post details  another Sunday Dave Green 5-star coming ever so close to breaking the limit that Dave seems to impose on his Sunday puzzles. It appeared in the 9/15/2019 edition of the Akron Beacon Journal.

My grid is unimpressed by the bypass and box marking. Only 5 cells claimed and 4 slinks marked. No clues. Did you do any better? Line marking will take some time.






It did. Two naked singles helped, but first  time through, I missed the  first hidden dublex Shdx2, and then the second one, Chdx9.



The grid, as  SW13 is confirming NW6 to trigger the collapse, shows why Green 915 is especially tough, even though it didn’t get through line marking.




The strong bv field, such an asset in advanced methods, allows two extensive ‘almost’ solutions to divide available candidates among them amicably, keeping the secret of which is true.

Missing the dublexes is not all bad. You reach the solution with this unique rectangle, Type 1, and one or both of






this BARN and/or naked triple.











Next time, we’ll start the review of the crudely titled FTSPAH collection with ftspah 4 and 24.  One is solved by the bypass, and the other requires several advanced moves. Your mission: determine which is which. Buy the book and keep the title away from the children if you’d like to get ahead of the review. It picks every 20th, ending in 184.


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Master Class 120 Completes the Update

This post concludes the review update of Tom Sheldon’s Master Class Sudoku and offers an amended review table.

The bypass on Master Class 120 is strong enough to keep line marking fill strings short. There are two naked singles, one springing a grid clearing breakout.



The bv scan picks up a Type 1 hidden unique rectangle immediately after line marking.

From the corner opposite the one free of extra candidates, two slinks in UR value 7 lie along the sides of the rectangle. If the UR partner value 9 in the opposite corner is true, the  7 candidate is not, and slink value 7 is forced in the adjacent corners. The remaining corner is 9.

In the placed rectangle,  the UR values in the corners can be interchanged without affecting any other cells, for a second solution.

In the original review’s highlights post,  a DIY UR analysis generates an additional removal, along with a swordfish.

This time, we add an XY extension to the original ANL for a quick collapse of Master Class 120,  starting with the trace below.










The table for the updated review of Master Class Sudoku  follows the plan adopted after the original review in which the results of applying the Sysudoku order of battle is reported in detail for every review puzzle.

Only the last two review puzzles survived Basic, but none fell victim to the bypass. Two additional puzzles, 130 and 140, were included in the table to suggest that the shift to advanced level was not by chance, although it was not mentioned by Sheldon.

Next, we take up another collection, just recently out, that is half basic level and half advanced level. Unlike Master Class, there is no trend, and you don’t know which level the next puzzle is in. I’m going to refer to this collection of unacknowledged authorship as FTSPAH, in place of the full title, which is F*CK! These Sudoku Puzzles Are Hard!

Before These Puzzles, however, you might try your Basic on a Dave Green Sunday 5-Star that thumbs its nose at the bypass, and comes very close to breaking through Sysudoku line marking into advanced territory. Regular readers know I have been featuring the Conceptis Sudoku puzzles from the Akron Beacon Journal, for 9 years.

Here is the puzzle in question, from The Beacon Journal Sunday 9/15/2019. My first solution featured a unique rectangle, a BARN, and a naked triple, but omitted critical moves. Correcting these, the 5-star grid reveals why it is such a challenge.

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PencilPress 81 and Master Class 110

This post concludes the review of PencilPress’ 500+ Sudoku Extreme Puzzles, and adds another puzzle to the review update of Tom Sheldon’s Master Class Sudoku. T

The final score was PencilPress Extreme 0, Sysudoku Bypass 10. If “Extreme” means requiring very advanced techniques to solve, then the PencilPress book is extremely mislabeled.  However, the cover and introduction do not display the overblown claims that “extreme” collections generally carry.  Once accepted as a collection of basic level puzzles requiring the best of the Sysudoku Bypass repertoire, this collection is worth your time. It does require concentrated, if routine, effort, and offers no excuse for guessing, or trials of any kind.

Bottom right, page 81 follows the other 9 review puzzles in bypass defeat, but has a basic challenge for you. Here is the bypass trace:

As you’re reading the trace, here is your grid as you finish your trace back on the first leg, and encounter NE8 as a cause. Where does it go and why? First, look at the other 8 placements, and answer those questions.  Then, if you did not spot NE8 this week, consider why not? It certainly isn’t “extreme”, is it? Also, note the fill of the South box.

Or if you’re among those who have the computer generate your candidates, and consider Sysudoku Basic a waste of time, you could save a lot of it by skipping Sudoku altogether.

The Master Class 110 bypass begins with a run of 1 placements, then a c2 4-fill NW3. This brings NE3 and another 4-fill  on r3, N9.








After this short, but remarkable bypass, a 2-wing arrives at the Close, where marking of lines on the unfinished rows or columns is completed.


This time the Close is on columns. The fill lists signal a tough line marking.








With all candidates in place, an easily spotted, potentially lucrative unique rectangle appears in the West.  It’s a type 4 UR, by the UR chart (Tools page).  One 3-slink partner must be true, so neither of the ceiling 2-candidates can be, unless you’re willing to believe that Tom Sheldon published an obvious multiple solution puzzle.

With all candidates in place, an easily spotted, potentially lucrative unique rectangle appears in the West.  It’s a type 4 UR, by the Tools chart.  One 3-slink partner must be true, so neither of the ceiling 2-candidates can be, unless you’re willing to believe that Tom Sheldon published an obvious multiple solution puzzle.

The collapse of Master Class 110 is immediate.

Next, we finish the review update with Master Class 120.




It might be a good time to look at an early Sysudoku assessment of the instruction in Tom Sheldon’s Sudoku Master Class. Tom would likely place UR types 3 and 4, described above, deep in his logical Twilight Zone.

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PencilPress 73 and Master Class 100

Two Basic level reviews continue with Pencil Press  bottom right, page 73 and Tom Sheldon’s Master Class 100.Two Basic level reviews continue with Pencil Press  bottom right, page 73 and Tom Sheldon’s Master Class 100.

Let’s begin with a Sysudoku survey on your ppbr 73. In your trace, did you add C6 before SW6, following the blog convention? Conventions help if you’re tracing to do comparisons.

Here is the grid after the run on 6. Do you continue with S8? Or is it (SW7, SW9)? The Sysudoku principle is to uncover all of a cause’s effects, before taking up the next cause. The next cause is the next effect on the current list, or the first effect on the next list.


The 73 trace is completed after a look at Master Class 100:


The trace looks normal, until you get into line marking and see two X-wings with no immediate effects. What is going on becomes more clear when you note that we are still in line marking, and there are possible X-wing eliminations in lines not yet marked.

X-wings are  detected as their second lines are marked. And yes, at that time, lines containing the X-wing’s eliminations may not have been marked.

That’s true of both of the X-wings spotted here.

The fish icons remain in place to “remember” the X-wing until all affected lines are marked. This technique that is not even possible in basic procedures that are detailed elsewhere, when there are any. The slink marking of Sysudoku Basic is essential to this X-wing filter in line marking. Nowhere else are there X-wing diagrams like the above.

There’s not much left to do on Master Class 100.

So how did you call it in ppbr 73? By virtue of the “cup” configuration it forms in the SW box, SW6 can be held responsible for a 79 naked pair, which 9r7c6 converts into (SW7, SW9). The bypass trace then reads:


Next post, the review of Pencil Press Extreme Sudoku  concludes with ppbr 81 at left.  The  last page with a bottom right puzzle is page 87.

The update of Tom Sheldon’s Master Class review continues with 110.

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PencilPress 65 and Master Class 90

This post continues the review of PencilPress Extreme Sudoku and the update of the review of Master Class Sudoku by Tom Sheldon.

Each PencilPress bottom right seems to have its own little novelty.  Hopefully, you found the one coming up in ppbr 65 after NW1, SW2, NE3, and SW3. If you consider the new SW box fill, and its missing values 4,5 and 7, two of those values see r7c1, placing the third value you know where.

Just as in line 3-fills, placement of one of the missing values gives us at least a naked pair in the other two cells.

Line 3-fills keep the placements coming in the remaining bypass trace.









Moving on to Master Class 90, we get clear examples worthy of The Guide about marking a partially line marked grid.



The first occurs on the second marked line r1, where a bv 38 matches another in c1. No more candidates can be added to r1c1, but the same cannot be said of r4c1, despite the fact that both 3 and 8 in r4c1 are box slink partners.  It’s not a naked pair yet.



You may remain unconvinced until c1 is marked, and 7 invades r1c4 to create a naked triple for NW5.







Line marking continues to the collapse with another naked triple and a 3-wing.








Here’s the basic trace.




Next week, the PencilPress Extreme review continues with bottom right, page 73 below.

PencilPress 73 Basic makes some interesting stops, and Pencil Press Extreme review finally breaks into box marking!

The update of Tom Sheldon’s Master Class review continues with Master Class 100, which illustrates again the enlistment of X-wings into line marking. That can be found nowhere else, until other Sudoku writers acknowledge the human engineering benefits of line marking itself.



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PencilPress Extreme 57 and Two Master Classes

Three more Basic victories are reported here with interesting traces. Looking ahead, the blog is heading toward more advanced collections, with this series being the final statement on Sysudoku Basic.

Ppbr 57 starts remarkably like ppbr49. C1 makes a wall for the value 1, forcing NE1. S1 is not first, only because of the convention to scan floors North to South and boxes West to East.

The bypass trace is stretched across the page by 3-fills.

Master Class 70 offers another unusual Basic start, in which values 1 and 5 are detected working together to claim two cells of NW.  Then 4 and 8  claim two cells in SW to place SW7.






In box marking, 70 soon gives up a rare gem. Look at NE at 6: NE. The four valus 2,3,4 and 6 are confined to four cells. It’s a naked quad. No other candidates can be added to these four cells, so NE4 is confirmed immediately.

Naked subsets can be found in box marking before all candidates are known. Hidden subsets require that all candidates of the unit be known.

Here is the basic trace, showing the follow up to NE4. Collapse comes in line marking. In the earlier review, Master Class 70 made it into advanced, for  a Sue de Coq, XY ANL, or a swordfish.



Tom Sheldon’s 80 was a highlight in the February 2013 review. Here is the grid with highlighted naked triple, as it appears in the update, in early line marking.





As evidence of an improved Sysudoku Basic, compare the trace of 2013 with this one.

Take into account that the difficult line marking of 2013 is not completed.




Including  Master Class 80 here, the next stop of the bypass express is at PencilPress Extreme br 73 at left and Master Class 90.

Both are basic level, but barely.

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PencilPress Extreme 49 and Master Class 60

Two reviews are running in tandem. PencilPress Extreme Sudoku is brings up a Sysudoku Basic issue on 4-fills. Tom Sheldon’s Master Class offers some advanced, but quickly settled examples.

Bottom right 49 brings up a Sysudoku Basic  policy question on its first move. If you’re working through the preview puzzle grids before the weekly post, what was yours? Was it E4 or NE1?

At first, I started with E4, having found no 3-fills, and no clues through 3. Later, after investing considerable time on the bypass trace, I realized that NE1 is forced in the c9 4-fill.

It doesn’t matter to you or to PencilPress, but but Sysudoku’s Sudent must report the choice most consistent with the systematic Sysudoku Basic.

On one hand, Basic doesn’t call for examination of every potential line with four unclaimed cells. There are too many, and success is too rare. But on the other hand, later stages often present me with something I overlooked in the bypass. We just considered how the trace enables going back and picking up right there. I do it without a twinge of guilt for not admitting my overlooks. The truth is, that in this blog, overlooks are only important if they reveal useful awareness.  Sudent’s trace starts with NE1, because the 4-fill is obvious enough for a glancing check on bypass 4-fills, and will certainly by noticed in later Sysudoku Basic. In keypad basic? Fill the grid with number scanned candidates and then decide.

But then, you might say that putting the 4-fill first is not consistent with Sysudoku Basic, and its practical policy mentioned above. That’s right, but NE1 still comes first, because the science of the puzzle is more important than human engineering policies for discovering it.

Here is the grid at the end of the first leg with a NE1 start.

In the corresponding trace, we need to pull out the most recent unused effect for a cause. Where is it? If you’re not confident in your answer, you can confirm it in the bypass trace at the end.

Not saying only one is right, below is a bypass trace starting with E4. The collapse is steady, with two pull backs to later list effects.

The trace starting at NE1 begins similarly, but has a steeper collapse, while arriving at the exact same conclusion. Causes and effects just fit together differently.





The difference in traces  shows why conventions for ordering lists are followed in blog traces. By following the same conventions as you write a trace, a useful match with the blog trace is more likely.

Turning now to Tom Sheldon’s Master Class Sudoku collection, the review update has good news and bad news. The updated Basic is more effective, but this means that two highlights of the original review are preempted. Here is the new basic trace of Master Class 60.


For what could count as a Basic highlight, here’s a snapshot at the placement of E9.

This comes in the marking of r9, in which two naked pairs are completed. At this time, only the r2 6f: line is left to be marked.



Next week, the PencilPress Extreme review and Master Class update continue with ppbr 57 left and Master Class 70 right.


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