My first Sysudoku review of 2018 is one of a host of new collection books with the same grid format, some with an unexplained rating system, some with listed authors A.D. Ardson and Rebecca Bean. Moito and Bean’s Extremely Hard Sudoku Volume 10 seem to share common difficulty rating system. The puzzle ratings are two decimal places, from a presumed zero, up to 1.00.
Sudoku: Road to Mastery is a collection of 400 puzzles without listed author, described on the cover as “Hard to Devilishly Hard”. It is divided into a “Hard Sudoku” section of 200 puzzles, ranging in difficulty from 0.60 to 0.74, and a “Very Hard Sudoku” section, ranging from 0.75 to 1.00. Each section is divided into four sets, I through IV, of 50 puzzles. Rather than my dart board selection of a start and a fixed size step to cover the collection, I tested the rating system as well by preselecting the 10 most difficult puzzles, according to the difficulty rating, from the “Very Hard” section. The result is the following review table:
The Moito difficulty rating is very inconsistent with the review results. The most highly rated puzzle fell in the bypass, and three more of the highest rated collapsed in box marking. The third above, III – 47, is the only contender for an extreme rating. I finished with a coloring trial, but perhaps I missed something you can find.
The 0.91 rated IV-6 has multiple solutions of a peculiar nature. Missing a boxline removal after a spectacularly irregular XYZ-wing, I reached a double solution on unique rectangle too late to reject it. The Moito solution was different, so I retraced, and found the omission. This time it was a different double solution on an extended unique rectangle formation of six bv, and this time, including the Moito solution. Related to earlier 2017 revelations, anything can happen with multiple solutions. They follow no inference rules. Details to come.
I happened upon two more glaring errors on the Road to Mastery. Puzzles III-5 and III-6 are destroyed by a sloppy paste-in of puzzles III-7 and III-8. Raising a more serious issue of trust, your homework III-47 above is identical to I-28.
Now to checkpoint your III-47. First a bypass typical of the Moito collection, reading:
C29, W4, W5, SE5. Yes, that’s it.
Box and line marking are routine, and the bv scan brings only this XY ANL with a grouped ER victim, or if you prefer, a grouped AIC ANL.
Next, fishing is bad on the X-panel, but an extraordinary set of 9-slinks can be assembled into an X9-chain ANL to trigger a SW/c2 boxline 9m removal to create a naked triple.
No fixes on the X-panel, but coloring around the 9-slinks produces three coloring clusters that do not bridge.
Conflicts in c3, c7 and r3c9 give bridging combinations:
not(green&red) => blue or orange, not(red&tan) => orange or purple, and
not(blue&purple) => green or tan. Bridge toxic sets don’t materialize.
With the X-panel showing little prospect for pattern restrictions, I’m ready for a color trial. From the bridge combinations, blue => tan. I go for a blue trial.
The trial trace reveals how blue inferences coordinate to force two 2’s into SE. Green => orange, but the marking stalls, but an XY chain from my updated railway wraps purple, with an immediate collapse to green, orange and tan.
Next post, I checkpoint your version of the I-4 bypass, and show several highlights reported in the review table above.
Also, four of the five Guide pages are up. They explain and demonstrate Sysudoku Basic via worthy examples.