This post starts the review of World’s Hardest Sudoku Book, tracing Very Hard 25, the only one rated a 1.00. The review will cover the highest rated 10, taking the rating down to 0.90. The lowest of the 200 is 0.76. Again, I know nothing about the rating, or the publisher, Sudokubooks. There’s no background information, or even a copyright notice, in the book.
Another reason to be prepared for surprises is that Strmckr, a Sudoku forum contributing expert, and an interested reader, has already sent in his solution notes on Worlds 25 in a comment. I can’t publish, or even look at, his note until this post is out, but an exchange may appear later, if only as 4/24/18 comments.
As for the my sysudokie trace on 25, it started in a scary way with a bypass of the bypass, and no clues from box marking, either.
But the outlook brightened with line marking, and on the first candidate grid, with an XY-wing generating an Ec9 boxline removal. Also, it was good to spot a BARN, even though its locked 4’s claim no victims.
Then on the X-panel, a 4-chain. In the XY-wing area.
The bv field in the East tower encourages coloring, and a 6-chain enables an expansion for a trap of 8r6c1.
A 6-chain/XY AIC almost nice loop and a second cluster don’t break the ice, but with the removal, . . .
. . . the 6 and 8-panel freeforms reveal single and compatible blue patterns.
Blue quickly confirms orange, and the solution.
The heavy reliance on XY-chains, the X-panel, coloring and patterns (templates) is typical sysudokie. The Strmckr approach is probably different and sure to be interesting.
For next week, the next two review puzzles are rated 0.92. One falls in the bypass and the other is a slippery monster.
You have a week to decide which is which, and to solve one in sysudokie basic. The basic traces of both puzzles will be posted next week.
Then we’ll continue on with the tougher, and perhaps, more on 25 solution paths.