FTSPAH 124 and 184 Close the Review


The FTSPAH review ends with a puzzle that might indeed frustrate experienced solvers, number 184.  It appears to require AIC building.  After the details, this post ends with a bypass trace of 124 which begins with three line 3-fills, and collapses in response to the first of them.

Hints of toughness are all along the basic trace of FSTPAH 184. There is no given 8, and puzzle resists the bypass, and denies a productive 3-fill.  There is no bail out in box marking, and 184 hangs tough in line marking  until a 6-fill clears some clutter before the last line, a 7-fill.

Here’s the grid at the naked pair r7s39. It has to be frustrating to search for advanced structures in the  keypad  version of this grid.

In this one, bi-value cells and strong links are marked and visible.  Anyone interested in tough Sudoku can learn this much ©PowerPoint.

The first advanced move is often an XY chain Almost Nice Loop, an XY ANL, as it is here.  The systematic XY railway method makes the spotting easy. Curves are drawn connecting like values to form the railway, which is explored for repeated values defining XY ANL and nice loops.

But now 184 somewhat justifies the cover warnings by demanding AIC building. In this phase, AIC chains are extended by all means necessary from slinks emerging from cells in the attempt to close a loop on the starting cell. With so many possibilities requiring detailed exploration, AIC building can be frustrating, and cursing doesn’t seem to help a lot.

A long 4-chain with several terminal pairs but no ANL victim is extended by a 6-chain into a bv boomerang confirming 4r8c4.

It looks deceptively easy, once you find it. The problem is following the humanly practical process that has you looking there.

 

 

Next, an AIC starting at 4r1c3 to 4r5c3 continues to find another slink until it returns, not to 3 or 6 for a boomerang elimination, but to 4 for an AIC nice loop. Now every outside candidate seeing both ends of any link is eliminated. Four more bv are created.

 

 

 

The bv added in AIC building make coloring much more attractive. In the first cluster, two candidates are trapped. They see the same value in one color, and share their cell with the other. Blue or green, these two are eliminated.

 

 

 

Next, either an r5 slink or the naked triple Cnt256 traps 5r4c5, and the resulting r5s38 removes 8r7c5.

 

 

 

 

 

 

 

In the expanded bv map, an XY ANL removes 3r9c1.

 

 

 

 

 

 

 

 

 

Then a second XY ANL removes 8r8c9, for c9s13 and SE5.

 

 

 

 

After

 

 

 

 

the blue departure brings immediate collapse.

 

 

 

 

 

 

 

 

 

As promised, the last word on  the FTSPAH  review is the bypass collapse of 124. The only possible frustration here is a discovery that you missed an effect in the rush of them.

 

The next collection up for Sysudoku review is Sudoku Super Fiendish, by Brian Challenger. It is a small collection of 100 puzzles. The 10 – puzzle sample,:  7, 17, 27, …, 97, covers 10% of the collection. For that reason,  the review will preview the givens for only the first review puzzle, SSF 7. To work ahead further, you’ll need to order your own copy.

You’ll have some extra time because the next two posts will deal with two entries in an interesting Sudoku puzzle contest, known on the Enjoy Sudoku forum as “the pattern game”. My friend Gordon Fick sent along two successful entries by Mike Metcalf based on the same pattern.

Here we will call them ‘mike 1’ (shown here) and ‘mike 2’ to follow next post.  If you are not already, you might pretend to be a pattern game contestant, and make up your own mike 2. Even with a solver to check each effort, it’s not easy.

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Two more Basic FTSPAH, 64 and 164


FTSPAH 64 exits in the bypass, and illustrates several bypass tactics that avoid the curse – invoking frustration that the  composers of FTSPAH puzzles claim on their cover. Its post partner 164 illustrates more bypass moves and survives for a few line markings.

Several 64 tactics show up as the bypass begins. Starting the box scan in NW, NW1 is not revealed until we survey the claims on the W box, forcing a 1-slink in Wc3, and a dublex crosshatch into NW, for W1. Our immediate response to the little square is to scan side lines r1 and c3 for values forced into the side lines of the square. Immediate response to little squares, filled box corners, walls, and 3-fills is the second tactic.

 

Moving on to value 2, two cross hatches fail, then a dublex crosshatch gets W3, and triggers the third tactic, which is to look back for slinks of previous values now converted to clues. That unwritten 1-slink leading to NW1 now produces W1. When value 4, clues E4 and E5 force these values into r4c14. N4 determines W4 and C5.

While text descriptions like the above explain the nature of Sysudoku marking, and specific solving events, it is much more effective to duplicate the traces while filling out the grid from the givens, as you anticipate and confirm each step, and let no action escape justification.

 

 

A Sysudoku trace trails off when complete placement is obviously no longer dependent on critical effects.

Turning to FTSPAH 164, an E box 3-fill gives a good beginning, followed by the first of several instances of two values working together to claim two cells in a box or line. In this case it’s 4 and 5 claiming cells of the W box and r5 line.  This leads to the grid shown here in which you are  to account for NE6. To add some handy names, it’s the NW four corners  and  N wall.

In the remaining bypass, some effects have multiple causes. Sysudoku conventions determined which cause gets there first, but unless you’re writing traces you expect others to compare with theirs, the conventions  don’t matter.

 

 

 

Here is the line marking grid at the naked single SE9 triggering the collapse.

 

 

 

 

 

 

 

Next time the FTSPAH review concludes with a third bypass wipe out 124, and with 184, the only puzzle to require AIC building. The FTSPAH review table below records five of ten basic finishes, three of these in the bypass. The advanced puzzles are dominated by XY chains and coloring. With the exception of 184, there’s nothing to justify the bravado of the title, and the breathless hype of the cover descriptions.

 

 

 

 

 

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FTSPAH 104 and 144


The review of the unspeakable FTSPAH continues with two more puzzles selected arithmetically.

The basic trace of FTSPAH 104 is Sysudoku Basic at its best. A near collapse in the bypass is extended by a deferred hidden dublex, which 104 survives, only to collapse in early line marking.

The hidden dublex leads the third run in a very productive bypass.

 

 

 

 

 

 

 

 

 

 

 

Imagine being at the SEhdx3  grid as a trace reader, with the task of accounting for SE3. Is your conception of the hidden dublex  sufficient for spotting this one. It may need tweaking.

 

 

 

 

Now just before the point where SEhdx3 is pulled out as a cause of the SW3 list, the trace identifies a hidden single. It must be spotted in reaction to SE2. Would you have spotted it without the trace?

When you do, you’re closer to the end than you might think.

 

 

FTSPAH 144 offers an early spotting challenge, namely N3 in this grid.

 

 

 

 

 

 

 

 

Later in line marking, something harder, a hidden pair r5hp59. A hidden subset is n values confined to n cells, and therefore claiming them. More abstractly, it’s n values that can be placed in only one way.

Much easier to spot, and the equivalent, is the corresponding naked triple r5nt246.

Here is the basic trace leading to these spotting chances.  The systematic and repeatable process of Sysudoku Basic, with a focused response  to each grid change, replaces unfocused search in a sea of candidates.

 

The horde of bv on the line marked grid invite two equally systematic advanced methods, XY chains and coloring.

The XY railway delivers less than expected, but the XY ANL elimination 4r1c8 is decisive in coloring.

 

 

In the blue/green cluster the trap at r3c8 leaves a hidden single 4 in c8.

 

 

 

 

 

 

 

 

Then

 

 

expands the cluster to wrap green in c7. The blue collapse is immediate

 

 

 

 

 

Next is FTSPAH 64                                                                                   and 164.

Both are finished in Basic, and one in the bypass.

 

 

 

 

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Systematic FTSPAH 44 and 84


This post demonstrates two more FTSPAH unlikely to frustrate anyone following the Sysudoku order of battle.

FTSPAH 44 begins with an unusually large number of givens, which generates a correspondingly large number of 3-fills. In fact, the givens offer both the box 3-fill NE[457] and the line 3-fill c7[357].

In Sysudoku traces, we mark 3-fills by naming the unit, then listing the three missing values. Line 3-fills are harder to spot, but are more often effective.  In the blog, these differences have led to the following marking conventions:

Line 3-fills are marked in the trace, and in the fill list space on the grid when the fill isn’t immediate.

Box 3-fills are marked only in the trace, ahead of line fills, and only when a fill occurs immediately.

Both types of 3-fill are marked ahead of the 1 to 9 values list.

FTSPAH 44 can be solved in the bypass by starting with the 3-fill c7[357], but the box 3-fill NE[457] is even faster. The first run includes three filled 3-fills.

In the grid at the end of the first run, the centered pencil marks are clue effects, in reserve for retrace causes.

In the grid at the end of the first run, the centered pencil marks are clue effects, in reserve for retrace causes.

The bypass trace follows below. There is no pause in which to utilize the c6 line 3-fill.

FTSPAH 84 starts with the value list, and nothing to say until value 5, then a series of head scratching, but rewarding effects.  Two unlikely hidden dublexi keep it going.  At the end of the first leg, a naked pair C36 combines with an earlier W6 for a one hdx. Then, on the second leg headed by NW8, an amazing hidden dublex. C4 on the first leg combining with NW4 on the second, deserves a spotting gold star.

Box and line marking are easy, and FTSPAH 84 goes on to deliver some advanced satisfaction.

First, on the line marked grid, a double hidden unique rectangle, Type 2b. Each 9-slink connecting floor to ceiling forces  a reversible solution rectangle when the other UR value is placed in opposite ceiling corner. For the r8 slink, that’s 3r9c8. For the r9 slink, its 3r8c8.

The Guide explains  how slinks work in the hidden UR.

 

In the same area, the 3r9c8 removal creates an XY-wing that pushes 84 over the edge.

 

 

The predominant 1,2,3 values hold their relationships close until the ball starts to unravel.

 

Next week continues the FTSPAH review with 104 and 144.

 

 

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The FTSPAH Review Begins With a Tour


Here I report on 4 and 24, the first two of 10 puzzles selected for the Sysudoku review of the FTSPAH puzzle book. Starting grids were displayed at the end of last week’s post.   I also explain a few things about the blog to a high school classmate, Jimmy.

FTSPAH has no acknowledged author, publisher, or copyright notice.  The full title is spelled out in the previous post, and that’s quite enough.  We are told it comes from Middletown Delaware, and that its “200 DIFFICULT puzzles … have the ability to cause even the most seasoned Sudoku lover to curse out loud in frustration”. Sysudoku readers are not expected to be all that seasoned. A Sysudoku review shows what can be expected by a human solver following the Sysudoku plan of attack. FTSPAH is revealed to be not that frustrating.

Here is the bypass trace for FTSPAH  4. The given 2-fill and 3-fill have so many effects, the puzzle is essentially solved before the 1-9 values list begins.

 

Jimmy, traces allow readers to reconstruct the solution one move at a time. The reader provides the reason for each move. That makes it simple and informative.  Experienced readers can write their own traces and compare notes.  For help, see Sysudoku Traces on the menu bar.

Sysudoku Basic on Ftspah 24 is more normal. The challenge here is patient focus on your knitting.

 

 

 

The first advanced stop is the BV map, where the XY railway produces a simple XY ANL.

Jimmy, there’s a glossary on the menu bar. It’s Sysudoku Speak.

 

 

 

 

Basic is the collection of candidates. Advanced is using relationships of candidates and clues to remove false candidates and confirm true ones. All basic procedures and advanced methods are explained in a hierarchy of pages, The Guide. For a listing of post titles, go to Titles.

Then an XY extension of the XY chain winds through the bv field to produce a very long nice loop. Every pair along the loop is toxic. Every link of the chain includes a true candidate, a placement in the solution.

By Sudoku rules, two placements of the same value cannot be in the same box or line. So any candidate in a box or line with both link candidates of the same value is removed.

The strong link network reveals itself in X-chains and coloring. Here we get a 2-chain ANL. In an ANL, an Almost Nice Loop, at least one terminal is true. If you see both, you’re out.

 

 

 

 

 

Coloring reveals a lot more of the slink network. Traps at r3c3 and r7c3 expand the cluster to force a wrap of green in r1c5. The blue army mops up.

One color is true, therefore seeing both colors of the same value is fatal. Two candidates of the same color in a cell is fatal for that color. That’s one type of wrap.

 

Here, the trap of 9r7c3 colors 9r7c1, and that traps 3r7c1, because blue or green is true.

Jimmy, I don’t usually repeat the fundamentals, but in this post it’s to show you around the place.

Next week we pair FTSPAH 44 at left with 84  on the right. One is basic level, the other, advanced. Find out which before the post comes out.

 

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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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