## Djape’s Hard Sudoku

This is a single post review of a book of very few words, Djape’s Hard Sudoku Book.   The book is a good size, the paper is good quality, and grids are clearly printed, with adequate margins. There’s no commentary inside, but the cover does provide good advice: “Remember: do not guess!

It’s just puzzles, 200 of them, divided into three sections. The first 64 are labeled “BRAIN”, the next 86 are “IQ” and the last 50, are “INSANE”. I decided to include 5 Insane’s , starting with 151, and taking every ninth. Thinking that a bit thin, I then worked back through the IQ’s, and left out the Brains. Stop that giggling. Anyway, here is the customary review table.

On average, it does appear that the puzzles are properly placed in IQ vs. INSANE. Four of five don’t survive sysudokie basic. But the one that does, gets beyond the bv scan to a beautiful kraken jelly. The unhyped title, Hard Sudoku, is appropriate.

You might want to see if you can bring it to heel sooner.   The givens are still in place on the jelly grid, after the Sue de Coq in SWc2 removes 3r1c2, leaving a hidden pair or naked triple in c2.

Two of the kraken jelly’s victims escape, but one of them betrays a peer in c8 by participating in a forcing chain to the fin. It could be a poster for kraken analysis.

The preselected INSANE examples are less advanced, and rather sane.

Here is the unique rectangle of INSANE 151. It’s a Type 4, in which the extra candidates of the slink corners are treated as a single cell forming a naked pair to take out 6r7c8. The same result can also be spotted by asking if 6r7c8, which clearly removes the 6’s, can get the 1 as well, leading to the forcing chain doing the job.

INSANE 178 got a little further in the SOM with this four cell BARN and WXYZ-wing. The bent region is outlined in blue. Three of the four wings are in the same unit as the victim and the hinge. The victims needs a grouped forcing chain to see the fourth.

Actually,  there also a sneaky little 186-wing eliminating a 6 from the other cell of the Cbox’s conjugate pair, again, by forcing chain vision.

I’m not even going to show it to you. It spoils my nice panoramic of the BARN.

That’s it for advanced level highlights, but if you enjoy challenging basic solving as much as  I do, you can wind your way through IQ 133, with its double X-wings and naked triple ending. In case you don’t have this Hard Sudoku Book yet, here is the starting grid. You may wind up getting one.

Next post is the third Unsolvable of the Sysudoku review series. It’s a chute table analysis of a single exocet in Unsolvable 186. To get there first, look back at the double exocet post on Unsolvable 181.