This post reviews the collection of 700 Frank Longo puzzles following the text in the Gordon Guide to Solving Sudoku. A review table summarizes the Sysudoku rating of 10 preselected puzzles, and one advanced puzzle is analyzed in detail.
The review table my preselected review puzzles suggests that the level of difficulty ramps up from #100 to #800. If you have this book, you may want to select a number range to suit your level of difficulty. In the table, the leftmost data column gives the number of clues/naked pairs produced by the bypass. Each naked pair is counted as two marks, to be consistent with marking counts in other columns. Four dashes mark the collapse.
Three were solved in the bypass, three more in box marking, two in line marking, and two by advanced methods. Of the advanced methods presented in the Guide, the reviewed puzzles offered three X-wings, but no other fish, and single XYZ-wing. I looked for Gordonian rectangles or polygons, and bilocation cycles, but none turned up in my preselected set.
If you go through the seven hundreds diligently, I’m sure you will find a more Gordonian events, but these results may be due to the Guide favoring rarely useful methods at the expense of frequently useful ones.
My track through #775 aligns with this opinion. My bypass trace is:
As expected, the bypass clues leave a very easy line marking
This brings a moderately tough grid for line marking, which uncovers a 9-wing:
The wing markers are left in place to keep 9-candidates out of c4 and c7 as the remaining lines are marked.
Guide readers, line marking X-wings is routine for sysudokies. You could pick up a lot of how-to information from the early Sysudoku posts.
The remaining line marking goes
The resulting candidate field is shown here, along with a finned 1-wing. The Guide doesn’t include finned fish, but its result in this puzzle is superseded anyway, so we’ll pretend it didn’t happen.
More news for guide readers: after line marking, sysudokies search for Sue de Coq and APE. The ample supplies of bv in Guide puzzles generate many of them.
The Gordon Guide does include XYZ-wings, but Guide readers should see what sysudokies use to find every XYZ, regular or constructed with forcing chains, and those with forcing chain victims. The crossed out hinges had the wings available, but not the connections and victims. That left one good one, a regular 231-wing.
Think maybe you should look this up? Click Find It! on the menu line.
The 231-wing removes one of two 1-candidates in c6, doing some damage. The trace of that damage is below. Update your grid first, then check it against the trace.
I’ll continue from here next time. We’ll search for Gordonian rectangles, polygons and bilocation cycles, and finish Gordon Guide 775. We’ll check out the X-panels, find some XY-chain ANL, do a little coloring , and step on a BUG.
Are you Gordonary solvers coming along? Please come on in, the waters fine!
I tried 625. After some easy steps, I found 1 XYZ Wing…then only easy.
I tried 775. After some easy steps, 1 Hidden Pair, 1 X Wing, one XYZ Wing, then some easy, then 1 XY Wing, then only easy
I tried 800. After some easy, I found one 2 String Kite, then just easy.
625 and 800 are quite comparable with puzzles from our newspaper while 775 is maybe a little tougher.
It’s great to hear from you. If I missed anything on 775, let me know.