Resuming posts after a quiet summer, this review identifies the title book as a basic level collection, offering an interesting challenge for the slink marking bypass, and little else. The brief introduction offers interesting historical facts, but is another example of ineffective solving advice.
Through my occasional Amazon scan, I picked up one of Mike Peterson’s Sudoku puzzle books, Volume 1 of an apparent series of “Very Hard” books. The back cover pictures six levels of these books, ranging from “Very Easy” through “Very Hard”, then “Extreme”. My magnifying glass reveals that volume 9 of each of these levels is pictured on this volume 1 book. Except for Very Easy Sudoku, only on volume 6. The review book has a publication date of April 1, 2016, written on the last page, and carries no copyright notice. Seriously?
Among the historical and mathematical data in his three page introduction, Mike drops in a one paragraph prescription for Sudoku solving, which I just have to quote, along with his example grid:
“The process known as ‘scanning’ involves analyzing cell for possible values, and filling cells where one number is possible. Scanning alone will solve most simple Sudoku puzzles. In the grid above, x = 1. Harder grids require the ‘forcing chains’ technique. Above, any value of a forces f=2, since
a=1 => b=8 => c=7 => f=2
a=2 => d=9 => e=7 => f=2.”
Did you follow that? If you did, it was only by finding the candidates first. Mike’s “scanning” assumes the number scanning I’ve constantly called out as inefficient and a generator of distracting clutter. After that, Mike’s advice is to pick a cell and follow the chains for each of its possible values, looking for a cell registering the same value for all chains. If you’re a computer, this trial & error is practical. If you’re not, it’s not. Not in real puzzles, that is.
After line marking, the final step in Sysudoku basic solving, the above chains are much easier to follow. Sysudokies don’t follow forcing chains. They take them as winks in advanced solving techniques.
As an example right here, a forcing chain enables 1r9c4 to “see” the third Z=1 candidate in the 891-wing.
Or if you prefer, how about completing an XY chain to eliminate 8r3c4, setting up a Snp19 to eliminate 1r9c4? In either case, the immediate collapse confirms 2r6c8, no T&E and no problem.
Getting to actual puzzles, my review selection provides no evidence that forcing chains, or XYZ-wings, or XY chains, are necessary for Peterson’s Very Hard collection. I took Very Hard 1 and every ninth puzzle, the series being 1, 10, 19, 28, . . ., 82. Starting with the slink marking bypass on each puzzle, I had 7 of 10 collapse in the bypass, and three in box marking. The consistent 17 givens suggests that the puzzles may come from the Royle collection that Mike cites in his introduction.
Very Hard Sudoku provides a good workout on the slink marking bypass. I enjoyed the book recently on some long airline flights, and shared it with grandson Daniel , who was equally successful. For your bypass homework, here is Very Hard 28, one of Daniel’s impressive victories, with a 2-D trace checkpoint to follow in the next post.
The mini-clinic on the slink marking bypass will continue with puzzles from Dave Green, the composer I follow daily in the Akron Beacon Journal. I’ve been modifying earlier Sysudoku posts to adopt the bypass fully. Last week, in the Friday, Saturday and Sunday paper, Dave posted two 4-stars and a 5-star that demonstrate especially well the techniques and value of the bypass. I’ll be checkpointing them with detailed traces to show the enhanced clutter fighting power of slink marking. And to clue you in on the pleasurable challenge of beginning efficient solving of basic level puzzles with the bypass. Don’t miss it, and do your homework!