James Forest’s Classic Sudoku 168 is a Basic level challenge. In this post, the Classic review is continued with the 168 box marked grid, and a basic trace carrying through the collapse on the second line of line marking. Then a report is given on the update of Manuel Castillo’s Only Extreme Sudoku 89, at its original post of October 17, 2017. Think of it as an invitation to get back into early posts.
The Classic 168 box marked grid has four lines marked, and four free cells in four more lines.
The middle line in the trace below is the box marking. Below that is every move, in order, of the collapse of Classic 168 into a solution, on the second line, column 1 of line marking.
It may be difficult for casual readers to realize what the trace is. The Guide pages will open the trace, and systematic Sudoku, to anyone.
Now about the review of Manuel Castillo’s Only Extreme Sudoku. It’s the second collection review selected for update, after KrazyDad’s Insane collection. These updates are undertaken on the hardest puzzles, and are reworked with backup from the Sudokuwiki solver available to everyone on Andrew Stuart’s site.
The original post of 10/17/17 solved Only Extreme 89 by a Single Alternate Sue de Coq, a Sysudoku trial innovation. Then it was shown that a freeform pattern analysis on one X-panel put four patterns in the pink slice and only one in the olive slice, and that the key clue isolated by the SASdC belongs to the single pattern. Either trial solves OnEx 89
The update solves OnEx 89 without trial, by full use of AIC building, including the recently recognized boomerang type of ANL.
Gratifying but not significant for the solution was this BARN, or Bent Naked Almost Restricted 4-set. BARNs are one of the friendly interpretive disputes between Sysudoku and Andrew Stuart.
Sudokuwiki found it and I didn’t, but stretching the definition of the WXYZ-wing to cover it, as the solver notes do, is not helping anyone to spot it.
At the bottom here is the SASdC. It’s logic is explained in the updated post.
After an easy finned X-wing and a 12-link boomerang, this ALS node eliminating ANL and an ALS node confirming ANL, or boomerang if you prefer, bring a respectably logical collapse.
C’mon, you have to look.
Next in the Classic review is 192 at right, and an updated solution of Castillo’s Only Extreme 3 below, originally posted 8/29/2017, where it demonstrates trials to extend coloring clusters onto slinked AIC segments. The updated solution avoids trials.