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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PencilPress 41 and A Well Hidden Dublex

In the review of PencilPress Extreme Sudoku, 41 is a another bypass blow out, with two steep collapses. Tom Sheldon’s Master Class 50 hands you a hidden dublex that is a challenge to spot and verify. We’re reviewing the PencilPress collection for the first time, and updating the Master Class review of 2013.

Let’s say you are reading the basic trace of  Master Class 50 and get to the  NEhdx5.

Your grid copy looks like this:


Now its up to you to explain how SW5 can create a hidden dublex 5 in the NE box, and where it goes.

What’s a “hidden dublex”? Welcome to Sysudoku, and look in Sudoku Speak or The Guide.


Now while you’re trying to think,


here’s the bypass trace for PencilPress bottom right, page 41:

With the effects of C7 posted, E9 triggers the remaining collapse. This is not extreme Sudoku, but PencilPress is right in their cover page advice to older Sudoku fanatics like me: “If you play Sudoku daily, you will start to see improvement in your concentration and overall brain power.”

Now before confirming your answer to the hidden dublex problem, here is the bypass collapse of Master Class 50:


OK, now about that hidden dublex, the pencil mark 5’s lead the way from SW5 to NEhdx5.

That’s looking four steps ahead, but it’s a regular follow up in the bypass, not a search. One slink leads to another. The only trick is to see that N5 excludes 5’s from Cr5 as well as Wr5, forcing a 5 in Er5. That means the 5 in c9 has to be in NEc9.


Sysudoku posted traces abound with subtleties like this. Many of them, like this one, are revealed in box marking.

Next week, it’s PencilPress 49 (left) with the same result, but a different profile of bypass collapse. Master Class 60 (right) falls in line marking, due to an improved Sysudoku Basic. This preempts a regular XYZ-wing and three XY ANL from the earlier review. If your Basic gets there better, show me.

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PencilPress 33 and Master Class 40

Another test of your Sysudoku Basic, and another witness that the PencilPress Extreme collection is basic level. On the other hand, that doesn’t make it dull. The bypass is actually a worthy challenge, but you have to experience it to know. Here is the bypass of the PencilPress Extreme bottom right 33.

Copy the givens from last post and make the moves, explaining how the obscure ones work. The walkthrough of Sysudoku basic in the Guide includes trace reading, but you can interpret it just by taking it as saying what you would do next.  If you really can’t follow it, there’s a page that lays out in detail the plan and structure of Sysudoku traces.


Now compare your bypass grid on Tom Sheldon’s Master Class 40 with this one.  Looking back, was the 3-fill 258 in r5  available in r5 when E17 was added? The trace can tell us.

In the bypass trace below, we look at the positions of C3 and C6, relative to E17.


C3 was placed earlier than E17, but C6 comes later. E17 made r5 a 4-fill. Going down the near collapse, C6 indeed triggers the 3-fill, just before the collapse dries up. Now we can look back up through the collapse to make sure no effects can be dragged out to the right to resume it.

The trace makes other comparisons possible. For example, Master 40 gave up a huge bypass, but escaped collapse, holding on until, in late line marking, it gives up a hidden triple.

Sadly, too many expert writers bury these basic dramas, dismissing basic work as “singles”.

Next week, it’s PencilPress bottom right, page 41 at left and Master Class 50 on the right.


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PencilPress 25 and Master Class 30 Update

This post gives the third in a consistent series of bypass collapses of the pre-selected review puzzles from 500 Sudoku Extreme Puzzles by PencilPress. This is verifiable fact because readers can reproduce the sequence of grids of a solution path,  using a Sysudoku basic trace, such as this bypass trace of ppbr 25

This post also begins  an update of the first Sysudoku collection review, in February 2013, of Tom Sheldon’s Sudoku Master Class.  In the original review, only highlight grid snapshots were published. When the update review is complete, a link to it will be inserted in the original post.

On Sheldon’s Master Class 30, which didn’t get a grid display in the original review, here is the line marked grid at a point where solution is assured.


The original review’s trace didn’t separate out the bypass, so it wasn’t evident how stingy the givens were.

From now on, I’m shortening the box marking lists by leaving out the “m” (for marking) on slinks of the list value.

That modifies the line marking above to

The Sysudoku trace remains unique feature in Sudoku literature, for some reason. Everyone is welcome to use it. It’s hard to appreciate what ‘implication by indentation’ does for the basic trace, unless you try to read the form it took when I started tracing.

Below is a sample of my earlier line marking trace, in which the operator ‘=>’ means “implying” and the nested series of uncompleted lists is represented by nested parentheses. You can encounter the problem by attempting to rewrite it in the indented form I write now.

Next time, its Pencil Press bottom right, page 33 at left, and Master Class 40, to the right.


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