I’m doing a quick sysudoku grading review of Frank Longo’s Level 4 collection.  It is based on 10 puzzles selected by prior rule. This post reports the general level, with backup data. The next will have some very entertaining snapshots on the review puzzles.

Frank’s collection was my choice for the second of many review’s because of his entertaining warnings to beginners and “mere Sudoku enthusiasts” to avoid tangling with these puzzles.  In his Level 4 Absolute Nasty’s Frank promises puzzles requiring multiple advanced techniques.  I think Frank is on solid ground to warn first time solvers to “slowly close the cover of this book and back away without making any sudden movements”.  But I urge them to take it home, with the cover securely closed, and start in on our blog until they are ready to tame the beasts within level  4.

The review series from Absolutely Nasty, Level 4 is every tenth puzzle, starting at number 1.  The review table gives the numbers of starting clues, clues, slink marks and naked pairs found in box marking, and bv left by line marking.  Then a brief comment on significant advanced level solving events.

If you missed or skipped over the Sheldon review table, I suggest you don’t make any sudden movements and quietly click the Reviews link for an explanation of review table conventions.

The review sample makes me want to continue working on the Level 4 puzzles.  It’s an adventure.  The finish can come at the close of line marking, or somewhere beyond coloring.   I put the collection at mid advanced level, and not extreme.

Frank does not drown you in a sea of candidates.  Basic solving is not burdensome, with predator events along the way keeping the candidate population in check.  There is a possibility of  collapse in line marking.  The Level 4 puzzles start you off with a generous number of clues, and on the close of line marking, you are likely to have plenty of bv for bv scan techniques.

Overall, I recommend Absolute Nasty Sudoku, Level 4 for sysudokies.  Contrary to Longo’s statement in the introduction, I don’t think that working the Level 4 puzzles will necessarily reward you with a good systematic theory of solving, but it is an excellent place to enjoy the one you can acquire on this blog.

About  the 9 solutions of #61 you surely noticed in the table, it may be unseemly to have as many unique rectangle opportunities and then allow a multiple solution, but that is not as contradictory as it sounds.  You can assume that obvious multiples with interchanged pairs are avoided by puzzle makers.  To detect  the more subtle forms of multiplicity that we see in #61, and in the recently posted USAPE puzzle, you or your computer have to do a lot more.  Frank Longo does not explicitly guarantee unique solutions in Absolute Nasty Sudoku, Level 4.  The possibility of multiple solutions doesn’t deter me from having fun with his Level 4 Nasties. It doesn’t even keep me away from UR eliminations.

The nice white space and “lay flat” binding are classy features for the genii who solve these puzzles on the fly.  They are for wasted on me, because I have to transcribe puzzles to a PowerPoint puzzle template on  my laptop.  Are those genii that solve without pencil marks or side visual aids finding logic or playing computer through backtracking T&E ?  They could be missing the fun.

The review concluded, here is the checkpoint on your homework,  Absolutely Nasty Level 4, #71. The box marking trace:

This leaves the dirty grid looking like this:

The line marking is easy, leaving you with the grid below for next post.

Your challenges now are two unique rectangles.  First prove that UR  r78c18 never goes deadly, because the candidates preventing it cannot be absent at the same time.  Secondly show that UR r9c78 can go deadly, and use this fact to generate decisive removals.

The next post will have my highlight snapshots from the review, including the 9 multiple solutions and how they were enumerated. And a checkpoint on you UR challenge.  Good luck!