Lucky Panda 192

This post details the basics and the easy solution of the fourth puzzle of the Lucky Panda Sudoku review, “insanely difficult” 192.  It’s not with a bv map.

The bypass starts with a 3-fill and immediately resolves two. Then slink marking is confined to the middle boxes.








Columns dominate in line marking, which is aided by two hidden singles.







Did you spot anything on the line marked grid?










Going directly to the bv map, two XY railway segments lead to removals.

Which diagram would you prefer for constructing XY chains: the universal keypad grid, the Sysudoku line marked grid, or the bv map? Be honest, now.



Of course you do have to reference the full grid for the candidate victims. The longer ANL eliminates 8r9c9, creating another bv. The decisive blow is a reverse boxline, with the 2r8c6 removal activating  box slink S2m to trigger a collapse.




Next week it’s all about LuckyPanda 240



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LuckyPanda 96 and 144

This post has a bypass trace to the solution of 96 in Lucky Panda 504 Sudoku Puzzles, and a basic trace and immediate coloring wrap for 144. The review will continue with single puzzles. It’s not mentioned in the text, but all the review puzzles start with 30 givens, an untypically high number.

LuckyPanda 96 is resolved in the bypass. The trace reveals a large contribution of 3-fills. The bypass comes close to drying up, before the rapid collapse.

Here is the grid as the trace ends with a solution assured. The lower case singles are effects not yet taken as causes.





The LuckyPanda 144 basic trace is more normal, taking matters into advanced.




The naked triple in line marking adds three bv.










Lucky Panda review puzzles consistently have a large number of bv cells. This makes XY-chains and coloring consistently effective. In 144 there is also the typically large number of slinks to support early coloring.

A blue/green cluster starting in the NE box spreads over the grid and wraps blue as two blue 5-candidates see each other. With green installed, the collapse is immediate.






Taken for what it is, the LuckyPanda collection is good Sudoku entertainment. The overblown labels of “extremely hard” and “insanely difficult” sell short what Sudoku has to offer. LuckyPanda Sudoku is recommended for those equipped in  Sudoku basic and exploring early advanced techniques.

Next is Lucky Panda 192.


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Lucky Panda Books Extremely Hard 48

LPB 48, the first review puzzle of Lucky Panda Books 504 Sudoku Puzzles, features an interesting hidden dublex and many unresolved 3-fills with fill strings trimmed by line slinks. The easy line marking closes with a DIY unique rectangle. A large bv field enables a coloring finish, with or without an XY ANL and a follow up UR.

It’s easy to dismiss the this large size paperback, especially when you see the back cover, and the two pages of explanations, basic tips and techniques. The collection is nothing like “Extremely Hard”, or “Insanely Difficult”, as claimed , and working all 504 will not bring you to a state of peak Sudoku mastery. Review puzzles 48, 96, . . . 480 are entertaining at the basic and early Advanced levels, and have instructive moments.

The layout is different: four puzzles to a page and answers to the eight puzzles of a spread at the bottom of the next spread. The review puzzles are on the bottom right corner of every sixth spread.

The Basic trace of  LPB 48 is promising. A host of 3-fills, many unresolved, stretch the bypass trace across the page, to a hidden dublex on value 9? And a breakout in the line marking close.

The bypassed grid reveals the story of the hidden dublex.

Taking out the SE9, you see that the S9 is confined to rows r78, a double line exclusion forcing SE9 into r9, while N9 keeps NE9 in c8.

Want to be a master of Sysudoku Basic?

Read traces.

Now a look at the Line marked grid, to pick up on something I just realized about 3-fills and line marking. In box marking, you can shorten the 3-fill strings by removing any value closed in the line.  Note how row fill strings of 3-fills are shortened by this action.


Also, Advance overlaps Basic with a variation of UR Type 1, as 4r5c4 removes both 4 and 6 from r78c4.

Both XY chains and coloring are favored by the bv forest. Coloring goes all the way from here, but an interesting side trail is XY ANL, with follow up




that removes 4’s and enables


another unique rectangle, Type 1.










Coloring resolves the near BUG and wraps blue for the collapse of LuckyPanda 48.









Next in the review, LuckyPanda 96 to the right,  is a bypass casualty.

The bypass trace will be here next week, with a solution of number 3, Lucky Panda 144 at the left.



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Only Extreme 390 is Advanced

This post finishes the updates on Manuel Castillo’s Only Extreme Sudoku with a less advanced OnEx 390.  This one is a better example of the Sysudoku XY Railway than was the original post. No trials were required in the ten puzzles pre-selected for the review. A plan for summer Sysudoku is posted.

The original review solution was posted December 27, 2017. At that time, the 3-fill was not a regular feature of Sysudoku Basic.

In case you would like to compare the basic paths to the same line marked grid, here is the updated bypass trace.


On the XY railway plot below, these are overlaid in black and red.

Instead of the original’s accidental spotting of an AIC nice loop, Sudokuwiki adjoins another XY ANL(red) to its first XY ANL (black).




On the XY railway plot below, these are overlaid in black and red.


Sudokuwiki’s third XY ANL can be traced on the railway starting in orange at r7c9 and following black then red to orange at r3c1.







The fourth XY ANL re-uses the XY wing, extending from 8r9c5 in blue and following red to r3c1 to continue in blue.








gAnd finally, the fifth XY ANL triggers an 8-wing. It starts from the same r9c5 cell and moves along red and blue to emerge in green.

Although the XY ANL sequence was favored by the solver, it is entirely  within reach of the Sysudoku approach of creating the railway and spotting ANL along it.

The systematic search can have different results, depending on which XY-chains are seen first.

Next, Sudokuwiki responds to the growing coloring opportunity with  an unusually extensive cluster. In the trap,  2r6c6 is removed by both green and blue, one of which must be true.

From that,

E2m => C2=> N4=> green,

and OnEx 390 is done.


Here is the updated review table for Emanuel Castillo’s Only Extreme collection.

The plan for the Summer 2019 blog is two collection reviews of “Extreme” collections, along with reports on blog improvements too long neglected. The objective is to have the blog ready to support the Guide as a paperback and e-book publication. The pages on The Guide, Sysudoku Basic, and Begin With the Bypass have been re-edited, and Box Marking is next. The Titles page is updated.

The next review is LuckyPandaBooks 504 Sudoku Puzzles, by Markus Buehl. My pre-selection schedule is 48 to 480 in steps of 48. The book is labeled as “Extremely Hard” on the front cover and “Insanely Hard” on the back, but if you are following the Guide, anticipate an entertaining exercise with ordinarily advanced methods, with a possible collapse in basic.

Here is LPB 48.



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Sudokuwiki Solves Only Extreme 347 by AIC

In the original Only Extreme review, OnEx 347 was an example of a coloring trial on a limited cluster generated by pattern analysis. In this update, Andrew Stuart’s solver demonstrates a solving path to a final coloring without trials, via AIC building.

The basic trace is updated to include 3-fills. In line marking, rows dominate with fewer unmarked cells.







On the line marked grid, the tight square of 5’s has the slink corner  for a hidden unique rectangle, Type 1.   If 3r5c7 is true, 5r5c7 is not, and two corners are 5, the other two, 3.  Now 3 and 5 interchange for a second solution.

Nothing is found in the bv scan or the X-panels,


before Sudokuwiki ventures into coloring with this trap. Both green and blue remove 9r2c7.  The resulting NEr1 boxline removes 9r1c5, expanding the cluster.

Entering AIC building, an AIC nice loop combines an XY-chain, a reversed bv, and two X chains, one grouped.




A grouped cluster expansion is accompanied by a long and winding AIC boomerang.








The removal enables a Type 2b uniqueness rectangle. If 9r1c2, the ur candidate opposite the slink is true, the other ur candidate 5r8c2 is true and 5r8c5 is false. The slink makes 5r9c5 true.

The 5/9 placements in the rectangle can be interchanged for a second solution copying this one everywhere else.

In the trap, 2r2c2 is rejected by both blue and green. And in the East, an XY boomer starts from r4c7.

Sudowiki piles on with a third AIC boomer, and after


an XY chain placing S5,








and                              after

the bv field looks ripe for another cluster.



The red orange cluster is extensive, but short lived. In r1, if red is true, both blue and green are false. Then in c7, if we accept orange, we have to take blue as well.

Next is the conclusion of the updated review of Emanuel Castillo’s Only Extreme Sudoku.


In case you want to try the last review puzzle OnEx 390 on your own, work with this  copy, because recovering the givens from the original review would give you too much in advance.

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Only Extreme 304 Scavenger Hunt

This post finishes the updated review of Only Extreme 304, displaying the Sudoku moves listed last week for the scavenger hunt.

The ALS X-chain boomerang starts with the 9-chain emerging from r9c7 and terminating on the 9 candidate of ALS 249, which slinks to the 4 value group. The group sees 4 in the starting cell, via 4-chain.





Independent of that elimination is this grouped AIC ANL,










and this one, the third grouped AIC ANL of the series.










This time the elimination expands the cluster and enables an XY-chain.









A boomer that didn’t work before is activated by the new c8 slink.










Then an AIC ANL turns 7r7c3 green and traps 7r8c3.










The AIC building series finally ends with an ALS boomer placing 8r7c6.









The S8 clue brings a naked pair 29, enabling a swordfish, which removes 2r1c7 for a hidden pair 29.









The hidden pair removals trigger an XY chain that starts a major expansion of the cluster.









Or a merge if a second cluster had already been started. The r8c3 trap turns 8r8c2 green, trapping 8r9c2. The naked pair r9s13 confirms 4r9c5, confirming N4 and S2.







The wrap brings immediate collapse.










Next, the update of the Only Extreme review continues with OnEx 347.


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Only Extreme 304 is AIC Level

This post and the next update Castillo’s Only Extreme Sudoku review with a solution of OnEx 304 without trials. Most of the solution path is in AIC building, the most challenging level of Sysudoku Advanced.

The only move prior to AIC Building is this Type 2 unique rectangle, which enables the limited cluster and intersecting XY chain extended in the original post into a decisive coloring network by six trials.

The placement 6r9c1 brings the NWc1 boxline removing 3r2c2.



Sudokuwiki AIC building starts with a possible boomerang that finds an ALS node to get to an AIC almost nice loop(ANL).








The starting links are recycled into a grouped AIC ANL.










The first boomer has an obscure start, but comes back in an XY-chain.









Moving right to left in the South tier, boomer 2 is double grouped. The key is the first group, making the following slink out of r9c2.






Now that first boomerang throw can be  recycled, including the same ALS, for an AIC ANL.








The breaking point is the nice loop, which introduces Medusa coloring to supplement Sudokuwiki.









The cluster expands and north tier AIC boomer links with it.




The 7r2c8 removal provides the needed slink for a hidden unique rectangle, Type 2.  If 4r1c7 is true, so is 7r6c7 and 4r6c8.  The slink then makes 7r1c8 true, and the rectangle’s 4’s and 7’s interchange for a second solution, no matter what happens elsewhere.

It’s been a lot to wade through, but Only Extreme 304 requires a lot more. For next week, I’m sending you on a scavenger hunt.  You are to collect, in this order, an ALS X-chain boomer(4r9c6), a grouped AIC ANL(4r7c6), another grouped AIC ANL(8r7c2), an XYchain(2r2c8), an X-chain extended XY boomer(2r9c7), an AIC ANL(7r7c6), a coloring trap(7r8c3), and an ALS AIC boomer (1r7c6), a swordfish(2r1c8), a hidden pair, an XY chain(2r2c1), and after a large cluster expansion, a wrap.

Short of the final advanced coloring, you could just load the starting grid into Sudokuwiki and tap your way through it. If you do that, look up unfamiliar terms in the Guide and compare Sysudoku explanations with Sudokuwiki notes and drawings over this post. The drawings and spotting notes will be in the scavenger awards post next week.



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