Here we briefly consider Nikoli claims of a “human touch” quality in their puzzles, and continue demonstrating Sysudoku basic technique with X-treme Sudoku review puzzles. These are presented by Nikoli as their toughest.

Is there a communication between Sudoku composer and solver that is nurtured by Nikoli composers , but is missing from computer generated puzzles? In X-treme Sudoku, Nickoli chief editor Kanamoto claims there is, in a very indirect way. He states that good composers “are always considering (the) solver’s feelings” and asks if a computer can “take into account the way a solver thinks”. In my opinion, the composer should be considering the logical unraveling of the puzzle and the beauty and elegance of that, rather than any emotional state of the human solver. And, if Nikoli masters truly understand how human solvers think, as Kanamoto’s question cleverly implies, they should compose a truly lucid and inspiring handbook on human solving, from basic through the most advanced.

Anyway, I felt no special connection to the master composer as I solved the 10 puzzles of this review. Maybe it’s my engineering approach to basic solving as a systematic process to get the human solver to the advanced stage as efficiently and accurately as possible. That’s the roses fragrance I smell in the solving of basic level puzzles.

To Nikoli’s credit, these puzzles do challenge the solver’s basic skills in diverse, interesting ways. They are worth your time. My only objection to Nickoli’s window dressing is that the puzzles are basic level, period.

So let’s take care of business. These reviews are a clinic in Sysudoku basic, in that you, the reader, can follow checkpoint traces on your own copy of the puzzle. You see the exact grid as each marking is made, and can pick up every “give away” the puzzle yields. There is even a likelihood of discovering one that I missed.

First, a trace of the collapse of X-treme 180 on box marking 8:

The trace of a collapse looks complex because of the large number of logical effects. But bear in mind there are a lot of cells to fill, and there is very little searching involved in the effort reflected in the trace. At each step it’s within view of the cell you are on. It goes fast when you are simply filling in the grid.

Usually, we just terminate the trace with “. . .” when it becomes very apparent that the collapse will continue to the end. The solution itself is of no consequence. The trace tends to run out of room on the page. It’s just the way it is.

Next up is the box marking checkpoint for X-treme 210. A quiet box marking suddenly explodes with a near collapse that runs out of horizontal space. Notice I had to jump back left into empty space to continue.

The grid with bv marked for line marking:

Next time, in addition to closing out X-treme 210, we’ll wind up the review with some highlight hidden subsets from X-treme 165.

New readers, especially, I hope you are following these checkpoint traces, on your own copy. If you have some experience with Sudoku, you can probably “catch on” to 2-D traces without directions. If not, look on the menu line.